Important forest insect pests and diseases with control ...

Important forest insect pests and diseases with control measuresImportant forest insect pests and diseases with control measures

Gyem Tshering and D.B. Chhetri

IMPORTANT FOREST INSECT PESTS AND DISEASES OF BHUTAN WITH CONTROL MEASURES

Important forest insect pests and diseases with control measuresImportant forest insect pests and diseases with control measuresImportant forest insect pests and diseases with control measuresImportant forest insect pests and diseases with control measuresCitation

Gyem Tshering, D. B. Chhetri, 2000. Important Forest Insect Pests and Diseases of Bhutan with Control Measures. Renewable Natural Resources Research Centre, Yusipang,Natural Resources Training Institute, LobesaMoA, Field guide 2000/1 August, 2000

Computer design and layout by Mr. Thrinang Wangdi, Lecturer NRTI

Funded by SDC/Helvetas Project BH 11

Coverpage: A blue pine partially killed and brooming caused by Dwarf Mistletoe

Published by:

Renewable Natural Resources Research Centre, Western Region-Yusipang,Department of Research and Development Services,Ministry of Agriculture,Royal Government of Bhutan

For a copy of the report, please address your request to:

Program DirectorRNR-RC YusipangP.O. Box 212Thimphu, BhutanTel: (975) 02-321600 EPABX 321602/3 Fax: 321601e-mail: [email protected]

Important Forest Insect Pests and Diseases of Bhutan

with Control Measures

Gyem TsheringSector Head, Forestry Sector

NRTI

D. B. ChhetriSector Head, Forestry Sector

RNR-RC Yusipang

August, 2000

DEPARTMENT OF RESEARCH & DEVELOPMENT SERVICESMINISTRY OF AGRICULTUREP.O. BOX 212, Thimphu, Bhutan

Tel. (975) 02 321 600/602/3 fax 321 601 e-mail: dbchetri@druknet.

RENEWABLE NATURAL RESOURCES

Research Centre Western Region : Yusipang

Field guide

Important forest insect pests and diseases with control measuresImportant forest insect pests and diseases with control measuresImportant forest insect pests and diseases with control measuresImportant forest insect pests and diseases with control measuresREPORT FORM

i5657ABSTRACT

Forests are adversely affected by climatic, human, pests and diseases that may be both of pathogenic and non-pathogenic origin. So, the foresters have a very vital function to promote, protect and conserve the forests by means of adopting appropriate preven-tive and remedial measures. Therefore, this field guide is prepared to assist the field people in meeting some of the above challenges. The field guide contains important description and colour photographs of diseases and forest insects of coniferous and broad leaved forests of Bhutan.

Keywords: forest, insect, disease, climate

ACKNOWLEDGMENT

We extend our appreciation and heart-felt thanks to Mr. Phunthso Namgyel, Ex-Programme Director, RNR-RC, Yusipang, Dr. Hansruedi Stierlin, Advisor, RNRRC, Yuispang and Mr. Dorji Wangchuk, Director, NRTI for their initiation and support in preparing this field guide; Royal Government of Bhutan and SDC/Helvetas for provid-ing the necessary fund. We are also grateful to Mr. Thrinang Wangdi, Lecturer, NRTI for the computer design, layout and printing the first few copies; Mrs. Sonam Yang-zome, Librarian, NRTI and Mr. Kencho Dukpa, Senior Forest Range Officer, RNRRC, Yusipang for providing necessary reference materials from the library. Lastly, we are indebted to many friends for their valuable comments in improving this guide book.

Important forest insect pests and diseases with control measuresImportant forest insect pests and diseases with control measuresImportant forest insect pests and diseases with control measuresImportant forest insect pests and diseases with control measures iii5455TABLE OF CONTENTS

PageABSTRACT iACKNOWLEDGMENT i TABLE OF CONTENTS ii TABLE OF ILLUSTRATION iii INTRODUCTION 1 Long - term objective 1 Specific objectives 2 INSECTS 2 General Introduction 2 Classification of Insects 3 The Life Cycle of Insects 7IMPORTANT NURSERY PESTS 8 Cockchafers (White grubs) 8 Cutworms (Surface caterpillars) 11 Crickets and Grasshoppers 12 IMPORTANT NURSERY DISEASES 13 Damping- off 13 Frost Injury 15 IMPORTANT FOREST PESTS 17 Ambrosia-Beetle, Pinhole and Shothole borers 17 Champ Defoliator 20 Chir Defoliator 22 Gamhar defoliator 24 Indian Gypsy Moth 26 Sal Borer 28 Sissoo Defoliator 32 Spruce Bark-Beetle 34 Teak Defoliator 40 IMPORTANT FOREST DISEASES 42 Dwarf Mistletoe 42 Root and Butt Rot 45 Root rot 47 REFERENCES 49

GLOSSARY 51REPORT FORM 56

TABLE OF ILLUSTRATIONS PageFig. 1 A typical insect with its body parts 3 Fig. 2 The different insect orders 4 Fig. 3 The life cycle of an insects with (A) complete metamorphosis (B) incomplete metamorphosis 7 Fig. 4 Adult Cockchafer beetles feeding on tender leaves 8 Fig. 5 A seedling with different parts 8 Fig. 6 Chafer grub feeding on roots of plant inside soil 8 Fig. 7 Young conifer seedlings affected by Damping-off 13 Fig. 8 Conifer seedlings damaged by Damping-off disease 13 Fig. 9 Frost damage kills young buds and needles in the upper crown of the tree 15 Fig. 10 Adults of Ambrosia beetles 17 Fig. 11 Wood damage and gallery systems of Ambrosia beetles 18 Fig. 12 Dust produced by Ambrosia beetles as a result of boring activity 18 Fig. 13 Entrance point of adult Ambrosia beetles 18 Fig. 14 Anatomy of wood 19 Fig. 15 Adult bug of Urostylis punctigera 20 Fig. 16 Badly defoliated champ leaves by U. punctigera 21 Fig. 17 The life cycle of Labeda nobilis 22

RADIATION FROST = ground frost - A form of frost caused by the rapid loss of temperature by radiation on cold nights.

RHIZOMORPH - A root like part such as the thread-like structures in certain fungi, consisting of strands of hyphae.

SAPROPHYTIC – Organism which lives on dead or decaying tisues.

SEGMENT – Different section of the body of the insect. ( Any of the parts into which something is or can be divided.)

SHELTERWOOD – Large trees left standing when others are cut to act as pro-tection for seedlings.

SILVICULTURAL CONTROL - Various silvicultural measures that are adopted for the prevention and control of insect pests that damage forest trees and nurs-eries.

SITE = Locality - Refers to an area/region/locality. A combination of physical and biological factors of an area that determine the vegetation it will bear.

SPORADIC - Occurring individually or at irregular intervals.

STAGE - Any definite period in the development of an insect; egg stage, larval stage, pupal stage, etc.

SUBTERRANEAN – Situated beneath the earth surface or under ground.

SUCCULENT – Plant that has fleshy leaves or stems in which it stores water.

SYMPTOM - An expression of disease or insect injury like abnormal growth or development of the tree.

VECTOR – Insect or animal that carries a disease or parasite and can pass it to other organisms.

VOLATILIZATION – To pass or evapourate in the form of vapour.

WITCHES BROOM - An abnormal proliferation of branches or twigs on a single branch.

ii

Important forest insect pests and diseases with control measuresImportant forest insect pests and diseases with control measuresImportant forest insect pests and diseases with control measuresImportant forest insect pests and diseases with control measuresiv 15253Fig. 18 Matured larva of L. nobilis with cocoon 22 Fig. 19 Adults of gamhar defoliator Calopepla leayana 24 Fig. 20 The life cycle of oak defoliator Lymantria obfuscata 26 Fig. 21 The Developmental stages of Sal borer Hoplocerambyx spinicornis 28 Fig. 22 Adult sal borer (Hoplocerambyx spinicornis) 29

Fig. 23 Frass at the base of sal tree due to boring activity of H. spinicornis 30 Fig. 24 The life cycle of Ips schmutzenhoferi 35 Fig. 25 Graph showing the generations and breeding flight in Bark-beetle 35

Fig. 26 Discolouration of conifer needles as result of bark-beetle attack 37

Fig. 27 Sawdust produced by Bark beetle at the base of attack tree 37 Fig. 28 Mother and larva gallery of Bark beetle in sapwood 37 Fig. 29 Larva of Hyblaea puera feeding on teak leaf 40 Fig. 30 Teak leaves damaged by H. puera larva 40 Fig. 31 A blue-pine branch infested by Dwarf mistletoe 42 Fig. 32 Fruiting bodies of Dwarf mistletoe 42 Fig. 33 Magnified fruits of Dwarf mistletoe showing seeds 43

Fig. 34 Witches broom formation on a tree as a result of Dwarf mistletoe infestation 44 Fig. 35 Fomes spp. with conks on tree trunk. 45 Fig. 36 Honey-coloured mushroom of Armillaria mellea 47 Fig. 37 Presence of dense, black “shoestrings” of rhizomorphs 47

Fig. 38 A mushroom with its typical parts 48

INTRODUCTION

In Bhutan, forests occupy about 72 % of the total geographical area of the country. The entire forests area is owned by the government and managed by the Department of Forest Services. Forest protection is given the highest priority, as it is considered the backbone of the country in terms of protecting environment, which is still in pristine conditions. Forests are also very important and beneficial for the well being of not only the people of a region or country, but of the entire human race.

Therefore, all necessary efforts should be directed to protect such intangible natural resources that are vital to the socio-economic development of a nation. Due to this very fact, the country is mandated to maintain the forest cover at a minimum of 60% in perpetuity.

In the earlier days, forest protection activity was concentrated only to forest fires control, as this was the only problem the people could foresee. Also, at that time there were limited skilled and qualified forest personnel to understand the magnitude of damages and protection of forests. Now with the advancement of science and technology, the understanding of the forest problems and protection have diversified to other areas. There is now concerted effort to study and understand the damages resulting from forest pests and diseases. These are the two most important agents that can endanger the natural resources in the long run.

Although the threats from the above agents were perceived many years back, there are still very limited information available to the forest resource managers on the symp-toms, damages, prevention and control measures of the respective pests and diseases. Therefore, this field guide is prepared to provide the useful and relevant information to field people, trainees/students on the protection and control measures of most important forests pests and diseases.

Long Term Objective

l To build up an information base for forest pests and diseases for the long-term protection and sustainable use of natural forests.

Specific Objectives

GENERATION - The development of insect from egg to adult.

GENUS - An assemblage of species agreeing in some characters or series of characters.

GLUTINOUS – A substance that is sticky like a glue.

GRUB - The larva of a beetle.

HIBERNATION – The inactive state of an organism to pass the winter months.

HOST - Plant infected or infested by a pathogen or insect.

HYPHA (plural-Hyphae) - One of the thread-like elements which form the my-celium of a fungus.

HUMMOCKS – A low mound or ridge of earth, a knoll.

INFECTION - The process or result of a pathogen invading host tissues.

INSTAR - The period or stage between moults during larval development; first instar is the stage between the egg and the first moult.

LAMELLATE – Compose or arrange in thin layers or lamellae.

LARVA, plural LARVAE - A young insect in an early stage of development.

LIFE CYCLE - The time between hatching from the egg and the emergence of the adult from the pupal stage. Most insects have 1 year life cycle.

METAMORPHOSIS - The development of an insect as it goes through different stages from egg to adult. Varies between different groups but is basically of two types: simple and complete. In the simple form wings develop externally and there is no pupal stage. In the complete form wings develop internally and there is a pupal stage.

MOULT - The casting of skin between instar.

MYCELIUM - The vegetative portion of a fungus. It is composed of hyphae.

NICHES – The area occupied by an organism in a habitat.

NURSE CROP – Leaving matured trees to give protection to seedlings.

NYMPH - An immature stage of an insect that does not have a pupal stage.

OOTHECA – The egg case of certain insect. e.g. grasshoppers.

OVER WINTER - The act of passing the winter period; usually inactive of in-sect’s life cycle.

OVIPOSITION - The act of laying eggs, either singly or in batches.

OVIPOSITOR – A tubular structure consisting of a pair of valve extending near the rear abdomen with which most insect lay eggs.

PARASITE – Any organism that grows, feeds and is sheltered on or in different organism that contribute nothing to the survival of the host.

PATHOGEN - An organism which causes disease in another organism.

PATHOGENIC – Which can cause or produce a disease.

PHEROMONE - A substance secreted to the outside of an insect’s body that serves as a chemical signal between members of the same species. They are usually airborne and act as sex attractants, alarm systems, aggregators or guides to food.

PHYTOPHAGUS – Insect or animal which eat plants only.

POOL FROST - The accumulation of a thick layer of cold air in a natural de-pression.

PREDACEOUS – Living by seizing or taking prey.

PREDATOR – Animal that lives by preying upon others.

PUBESCENCE– A covering of soft, short hairs on certain parts of insects or plants.

PUPA, plural =PUPAE - The resting inactive stage between larva and adult.

PUPATE - To become a pupa.

Important forest insect pests and diseases with control measuresImportant forest insect pests and diseases with control measuresImportant forest insect pests and diseases with control measuresImportant forest insect pests and diseases with control measures

2 35051

Fig. 1 A typical insect with body parts

l The field guide will serve as reference to field people and training institutes.

l The field guide should enable field people to identify the important forest pests and diseases with reference to economical importance, life cycle, symptoms and damages.

l The field guide should assist the field people to understand and undertake the necessary measures to prevent and control further spreading of the pests and diseases.

INSECTS

General Introduction

Insects form by far the largest part of all groups in the Animal Kingdom. About three-quarters (70%) of all known species of living animals are insects. Scientists have so far named and described approximately 650,000 species of insects. The total number of insect species is yet to be discovered in the whole habitable world. Entomologist have estimated insects species to be present between 10 to 25 millions.

Insects belong to a group of animals known as arthropods (meaning: jointed legs). They are related to millipedes (Diplopoda), centipedes (Chilopoda), spiders, scorpions, ticks etc. The insects are mostly land living creatures with some exception like the crustacea (crabs, shrimps, etc.) that are by contrast mostly aquatic.

During the course of millions of years, insects have evolved into a bewildering variety of shapes and forms adapting to particular life-style. The most important characteristics of the insect is its feeding habit. A great majority of the insects are herbivores, while others are saprophytes or scavengers, carnivorous and omnivorous. Therefore, the study of insect is of great economical importance to man in competing with the natural resources.

What is an Insect? Insect is a small animal with six legs and a body in three parts. The insect is made up of several segments each comprising of a ring of plates. The whole body is divided into three or more clearly defined areas each made up of several seg-ments like head, thorax and Abdomen (Fig. 1)The head is made of six segments that are fused together into a single capsule and it is not easy to distinguish each segment very easily. The prominent features of the

head are large compound eyes, a pair of anten-nae and set of mandibles. The thorax consists of three segments. Each thorax bears a pair of jointed legs and in addition each of the hind two segments bears a pair of wings. The Abdomen is the least adapted body of the insect. It com-prises of eleven segments. The ninth segment bears penis in male and ovipositors in female. The Abdomen of an insect never has legs but abdominal legs may be present in some larval forms.

Classification of Insects

Insects with a wide geographical distribution found in many different countries may be known by a number of different common names. In

order to reduce confusion, the scientific community has for many years adopted a system of naming plants, insects and animals with a unique double name of Graeco-Latin origin that distinguishes it from every other species. The two names comprise of a generic and a species name.

The genus is a group of related species. Further closely related genera are placed in the same family. Group of similar families are lumped together into a larger group known as orders. Modern classification divides the whole class of insects into 29 or-ders. In some orders there are further sub-division between the order and family level into sub-orders and sub-families. The orders have the ending -ptera, family as -idae, sub-family as -inae and super-family as -oidea.

Example of classification of an insect is given below. Kingdom - AnimaliaPhyllum - UniramiaClass - InsectaOrder - LepidopteraFamily - NoctuoidaeGenus - AgrotisSpecies - ypsilonThere are many orders of insects that are important to foresters. Only those orders and families that are of interest to foresters are mentioned below. (Fig. 2)

A. Dictyoptera e.g. Praying mantids

Harde/Severa. Der Kosmos Kaferfiihrer, Die Mittelleuropaischen Kafer. Amann, Kerfe de walds Mu\iinchen, Weihnachten, 1959.

Hans E. Laux, Ebare Plize . Und ihre giftigen Doppelganger, Stuttgar: Franckh, 1986.

GLOSSARY

ABDOMEN – The part of the body behind thorax.

ADIOTIC – Not biological or not related to living organisms but natural factors.

ADVECTIVE FROST - A type of frost formed by the effect of cold air coming in from elsewhere.

ANAEROBIC – Not needing oxygen for living or existence.

BARK BEETLE - Any beetle that feed exclusively in the cambial region of stems, or branches and spends most of its life cycle there.

BEETLE - An insect belonging to the order coleoptera with wings covered and pro-tected by hard outer wing cases.

BIOLOGICAL CONTROL - Controlling a pest with the help of biological agencies.

BROOD - All the offspring from eggs laid by one series of parents which mature at about the same time.

CALCAREOUS – Substance that contain calcium.

CANKER - A defective lesion on a stem, branch, or roots; the cambium of which has been killed.

CARNIVORE - A group of animals or insects that prey upon other animals or insect species. There are also a number of carnivorous plants that prey upon small insects.

CARNIVOROUS – Meaning meat eating.

COCOON - A covering spun or constructed by a larva as a protection to the pupa.

COLONY - Group of one or more species that live in an area.

CONGREGATE – To come together in a crowd.

CONK - A fruit-body of a wood destroying fungus, which projects to some degree beyond the substratum; also a sterile projecting fungus growth that resembles a fruit body.

CREVICES – Cracks or little hole in rocks or trees.

DECAY - Wood decay: Process or result of degradation of wood by fungi, bacteria or by yeast.

DECLIVITY – A descending slope with teeth like structure at the anterior por-tion of the insect.

DEFOLIATOR - An insect that exclusively feeds on foliage.

EPICORMIC BRANCH (SHOOT) – branches originating in clusters from a dominant or adventitious buds on the trunk of a tree or an older branch due to adverse influences like fire, suppression, mistletoe infestation.

FORKED – The main stem of a tree dividing into two prominent branches.

FRASS - A solid larval excrement.

FRUCTIFICATION – The producing of a fruit.

FUMIGANT – A gaseous or readily volatilizable chemical which is capable of destroying vermins, insects, bacteria and mould. It has the characteristics of rapid diffusion through air in closed or confined places.

FUNGUS (Plural – Fungi) – Simple plant organism with thread-like cells (such as yeast, mushrooms, mould) and without green chlorophyll.

Important forest insect pests and diseases with control measuresImportant forest insect pests and diseases with control measuresImportant forest insect pests and diseases with control measuresImportant forest insect pests and diseases with control measures4 54849

Fig.2. The different insects orders A:Dictyoptera, B: Orthoptera, C: Phasmids, D: Isoptera, E: Homoptera, F: Heteroptera, G: Lepidoptera, H: Thysanoptera, I: Coleoptera, J: Hymenoptera, K: Diptera.

secondary myceliumwithin thesubstratum

pileus

gill

annulus

stipe

Fig. 38. A mushroom with its typical parts

This order includes cockroaches and the praying mantids. Praying mantids fall under Mantodea sub-family. The female of praying mantids lay eggs in ootheca attached to the twigs or other objects. Each female sometimes produces as many as over 20 egg cases. Mantids have 3 - 12 instars and life cycle is about a year. Praying mantids are carnivorous and beneficial as it feeds voraciously on flies, caterpillars, grasshoppers.

B. Orthoptera e.g. Crickets, grasshoppers and locusts

They are mostly phytophagous but few species are predaceous. Some like the locusts are capable of sustained flight and are known to be very destructive to crops and veg-etation. The eggs may be laid in or on the ground or in plant tissues separately or may be enclosed in a cylindrical pod. There are generally 4 - 6 instars in some species. In most cases the species have one life cycle per year.

C. Phasmida e.g. Stick and leaf insects

Phasmids are elongated, narrow and large insects. They resemble twigs and leaves on which they live and feed. In Phasmida two main types exist viz. stick or walking insects (Bacllidae). The colour and appearance of the insect is also similar to twigs. The leaf insects are flattened and leaf-like, winged and lamellate expansion of the legs. These insects can defoliate trees when present in large number.

D. Isoptera e.g. Termites or White ants

Isoptera are mostly confined to warmer parts of the world. They mostly feed on wood and are very important to foresters. They are social insects and live in well organized colonies. Each colony contains several castes or different individual members - repro-ductive males and females (queen), soldiers and workers.

Although termites live in dead logs, some genera bore into dry wood and are therefore important pests of wooden furniture and buildings. Few species are important pests of living trees whilst others are more important pests of felled timber and logs. In the drier parts of the tropics, subterranean termites cause considerable damage to planted seedlings and saplings by girdling the young trees at the ground level. Such damages take place during dry season when the plants are water stressed.

E. Homoptera e.g. Cicadas

This includes Cicadoidae (super-family) and its families Cicadidae. Cicadacae are large insect that produces sound by a pair of organs situated on the ventral side of the basal abdominal segment. The cicada with its ovipositor punctures or make a slit on the twigs of trees to thrusts its eggs. The nymphs hatch from eggs and drop to the ground. They burrow into the soil to a depth of about 50 cm and feed on the sap of the root of trees. In its last instar the nymphs digs its way out of the ground, usually climb to a tree and fastens its claws in the bark and moults. The life cycle may vary from one to two or more years depending upon the climatic conditions and species of insect.

F. Heteroptera e.g. Bugs

The bodies of these insects are flattened and the wings are folded flat over the body at rest. The insects belonging to this group are not uniform in sizes. The insects are dull in colour with green and brown. The insects produce pungent secretions in special ‘stink glands’ near the hind legs. The insects themselves have an unpleasant taste and smell due to such secretion. The secretion is a form of protection to the insect. The secretion is also passed to the plant on which the insects crawl.

G. Lepidoptera e.g. Butterflies and moths

This order of insects has complete life cycles: egg - larva - pupa - adult. Adults are generally not injurious to plant as they feed mostly on fluid substances like nectar.

Bevan, D. 1987. Forest Insects. A guide to Insects feeding on trees in Britain, HMSOPublication Center, London.

Bigger, M. 1988. The Insect Pests of Forest Plantation Trees in the Solomon Islands. Overseas Development Natural Resources Institute, Central Avenue, Chatham Mari-time, Chatham, Kent ME4 4TB, UK.

Chhetri, D.B. 1998. Manual of Instruction for Prevention, Detection and Control of Forest Insect Pests and Diseases Outbreak. RNR-RC, Yusipang, Thimphu.

Chhetri, D.B. 1995. Observation Trial on Dwarf Mistletoe Infestation on Blue pine; Tsenden Vol.5, No.1, Dec. 1995, 22-25.

CSO, 1996. Statistical Year Book of Bhutan, Planning Commission, Thimphu.

Dewadi, A.P. Madhya Pradesh main Sal Borer Samaysa tatha Neanteran, Bhupal, 1998.

FRDS, 1998. Guidelines for Controlling of Bark beetles above Chang Gidaphug Area, FSD, Thimphu.

Hangle, S. K et al. 1987. Field Guide to Diseases and Insects Pests of Idaho and Montana forests, US Dept. of Agriculture Forest Services, State and Private Forestry, Northern Region, P.O Box 7669, Missola, Montana 59807.

Hutacharen, C. et. al (edit). 1990. Proceedings of the IUFRO Workshop on Pests and Diseases of Forest Plantations. Regional Forestry Officer, FAO Regional Of-fice for Asia and the Pacific, Maliwan Mansion, Phra Atit Road, Bangkok 10200, Thailand.

Khana, L.S 1982. Forest Protection Khana Bandu, Dehra Dun, India.

Negi, S.S. 1995. Handbook of Forest Protection, International Book Distributors, Dehra Dun, India.

Negi, S.S. 1996. An introduction to Forest Pathology, International Book Distributor, Dehra Dun, India.

Schmidt, L. 1998. Insect of Forest Seeds. Technical Note no. 51, Danida Forest Seed Centre, Krogerupvej 21, DK 3050, Humleback, Denmark.

Schmutzenhofer, H. 1985. Consultancy in forest Entomology, FAO, 1985.

Schmutzenhofer, H. 1988. Emergency assistance in Controlling Forest Destruction by Bark beetle, Consultancy in Forest Entomology, FAO, Rome.

Schmutzenhofer, H. 1989. Forest Entomology Draft report. World bank, Forestry II-BHU 1900.

Schmutzenhofer, H. and Chettri, D.B. 1986. The Trap Log System, Forest Protection Cell, Management Division, Thimphu.

Schmutzenhofer, H. and Chettri, D.B. 1986. Information and Control Methods, FAO/BHU/83/022, Forest Protection Cell, Management Division, Thimphu.

Stebbing, E.P. 1914. Indian Forest Insects. M/s Bishan Singh Mahendra Pal Singh, New Connaught Place, Dehra Dun, India.

USDA. Forest Insect and Disease Identification and Management. USDA Forest Services, Northern Region, Cooperative Forestry and Pest Management, Idaho Dept. of Lands, Insects and Disease Control.

Nayar, K.K, Anantha Krishnan, T.N and David, B.V. General and Applied Ento-mology, Tata McGrew Hill Publishing Company limited, New Delhi.


Fig. 3. The life cycle of an insect with (A) complete metamorphosis (B) incomplete metamorphosis

Fig. 37. Presence of dense, black “shoestrings” of rhizomorphs

Fig. 36. Honey-coloured mushroom of Armillaria mellea

The larvae are of great economic importance as it primarily feeds on plants. A great number of species feed upon leaves and are capable of completely defoliating a tree. Other species bore into buds, shoots, fruits, seeds and a few even attack roots.

The principal families that are important to foresters are: Cossidae, Torticidae, Pyrali-dae, Psychidae, Nymphalidae, Lycaenidae, Papilionidae, Hesperiidae, Geometridae, Uraniidae, Sphingidae, Lymantriidae, Arctiidae, Nolidae and Noctuidae.

H. Thysanoptera e.g. Thrips

They are small to minute insects with piercing-sucking mouthparts. They live in great numbers and often attack flowers, buds and leaves. They have the ability to act as vectors of some bacterial, fungal and viral diseases of plants.

I. Coleoptera e.g. Beetles

Coleoptera is the largest order of insects with over 300,000 species. The larvae feed on wood or wood products and the order is of great importance to foresters. Some species bore into bark or wood of living trees although majority of them are wood feeding attacking only dead or drying trees.

Over more than 100 families are described of which most important to foresters are: Scarabaeidae (Chafers, dung beetles, rhinoceros beetles etc.); Buprestidae (Jewel beetle); Elateridae (Click beetles); Anobiidae (Furniture beetles); Bostrichidae(Round powder post beetle); Lyctidae (Flat powder-post beetle); Cerambycidae (Longicorn beetles); Chrysomelidae (leaf beetles); Anthribidae; Brenthidae; Curculionidae (Weevils); Platypodidae (Ambrosia beetles); Scolytidae (Ambrosia and bark beetles).

J. Hymenoptera e.g. Bees, wasps, ants

Hymenoptera are beneficial insects because they feed on other insects and can therefore be used for biological control of other forest pests. Sometimes, the larvae are similar to Lepidoptera caterpillars and do great damage to trees, but are not well represented in our forests.

K. Diptera e.g. Flies

Diptera are insects with only one pair of visible functional wings. Some larvae feed in rotten wood and others are carnivorous and feed on larvae of bark feeding Coleoptera.

Tachinidae is an important family to foresters, as it is parasitic and attacks caterpillars of many species of Lepidoptera that feed on trees.

Life-cycle of Insects

Insects undergo metamorphisis during the dramatic change from juvenile to adult. Metamorphisis can be of two types viz. complete metamorphisis and incomplete metamorphisis. The first type of metamorphisis passes through all stages of develop-ment (egg - larva - pupa - adult) (Fig. 3A). The second type often called as Gradual or incomplete metamorphisis occurs with interim nympha stages, which by-pass pupal stage (egg - nymph - adult). (Fig. 3B)

In insect species with complete metamorphisis larvae are the most destructive as compared to adult. But in insect species with gradual or incomplete metamorphisis both nymphs and adults are very damaging.

The duration of generation turnover or life cycle depends on species and environ-ment. Under favourable environmental conditions some species may complete their life cycle in less than a month, while some may take several months. Insect species having several generations per year (multivoltine) emerge quickly after pupation, but those with only one generation per year (univoltine) stay dormant as pupae inside cocoon for several months until next favourable season.

IMPORTANT NURSERY PESTSCOCKCHAFERS

(White grubs)

Introduction

ROOT ROTArmillaria mellea

Introduction

Armillaria mellea is distributed worldwide and occurs both on conifers and hardwoods. It is perhaps the most dangerous subterranean parasite of trees. This fungus is also a serious disease of heartwood and sapwood.

Life History

The fungus occurs commonly as a saprophyte in many conifer species. The fungus commonly invades stressed trees and trees infected by other root pathogen. The fun-gus survives on dead organic matter like decayed stumps and roots. It spreads from these food bases to the root of living trees either through direct root contact or by rhizomorphs. From the infected roots, the fungus colonizes the root collar, kills the cambium and eventually girdling the tree. It generally attacks trees of low vigour and maintenance of stand vigour is an effective means of controlling the fungus.

Symptoms and Damages

l The trees loose their needles beginning with the oldest and progressing to the youngest.

l The colour of the tree crown uniformly changes to yellow or red.l The most distinctive feature is the thick, fan-shaped mat of white mycelium in

the root region.l Presence of honey-coloured mushrooms and rhizomorphs on the outside of

infected roots (Fig. 36 & 37). l In advanced attack the wood becomes soft and spongy with dense mycelium

threads (Fig. 38). l The fungus finally decays roots and kills cambium in roots and root collar.

l The infected trees are susceptible to bark beetle attack.

Control Measures

l All old stumps should be removed in plantation site that has risk of A. mellea attack.

l Since the fungus is prevalent in moist and damp site, proper choice of sites can minimize the fungus outbreak.

l The attack can be reduced by raising mixed plantation and introduction of disease resistant species, as the parasite is often specific in its attack.

l Spread of root disease under the soil is prevented by making isolation trenches in between rows of trees.

l Wider spacing and regular thinning may minimize the incidence of the fungus infestation.

l The outbreak of the fungus can be controlled by timely removal of killed trees and bushes.

REFERENCES

Bakshi, S. 1964. Forest Pathology. Government of India, New Delhi.

Beeson, C.F.C. 1941.The Ecology and Control of the Forest Insects of India and theNeighboring Countries. (Reprint 1961) Govt. of India, New Delhi.


Fig. 4. Adult Cockchafer beetles feeding on tender leaves

Fig. 6. Chafer grub feeding on plant roots inside soil

roots

leaves

stem

collar

Fig. 5. A seedling with different parts.

Fig. 35. Fomes spp. with the conks on the tree

Important forest pests and diseases with control measures

Cockchafers belong to the Melolonthidae family of the Coleoptera order. There are several species of chafer beetles and their habits vary depending on species and locality. The adults (Fig. 4) are least damaging to plants. It is the grub that causes much destruc-tion to seedlings (Fig. 5) in the nursery. The species has a wide range of distribution and is economically important to foresters in terms of loss of seedlings in nursery.

Life cycle

The adult lays eggs several inches deep inside well prepared and loosen soil. Under suitable environmental condition, the eggs hatch into larvae called ‘White grub”. It is usually curved in the form of “C” (Fig. 6). The larval stage is passed in rot-ten humus or in soil. The larvae feeds on small roots

of plants. The fully grown grub can measure up to 2.5 cm in length. The grub remains buried under soil causing damages to the under ground part of the plant till pupation. Pupation takes place in the shelter of the larval skin without the formation of special cell or cocoon in the soil. The pupal period lasts about a month. The immature beetle remains in the soil until suitable climatic conditions permit emergence and flight. The adult beetle is plump-bodied measuring 2 inches in length. It is usually light to dark brown in colour. The adult beetles feed on trees at dusk and do not fly by day.

Damages

Cockchafer grubs are mainly root feeders. They kill seedlings by destroying rootlets or removal of bark of taproots. Adults feed on tender leaves.

Preventive measures

l Seedbeds should not be prepared in hot weather or beginning of monsoon to prevent oviposition.

l Sowing should be done in autumn, winter or spring when the beetles are not on wings and cannot lay eggs.

l If soil working is done during oviposition period, the soil should be covered with a layer of charcoal, sand or sulphur. Sowing should be done by removing the covering in line and putting it back after sowing. Cover should be removed after the danger period is over or the soil is compacted.

l Transplant beds that are not immediately used should be watered with crude oil or kerosene emulsion. Rigorous watering must be done for the chemical to penetrate deep into the soil.

l Avoid weeding during the flight period of the beetles, as it facilitates oviposi-tion.

l To prevent wandering of grub from neighboring beds, the bed should be edged with planks as deep as possible and covered with 5 to 6 mm wire mesh.

l Grubs can be prevented by treating soil with 0.8 % acetic acid at the rate of 9 lits. per sq. m. This will also check damping off.

Control measures

l The white grubs are big and can easily be picked up by hand and destroyed.l Some of chafer grubs travel at night and they can be trapped by sinking tins

or earthen pots beside the nursery beds.l If the grubs are present, the nursery bed can be flooded with water. The grubs

will come to the surface due to suffocation, and hand picking is suggested.l Some chemicals such as carbon disulphide, CaCN, Nepthaline, Acetic acid,

Aldirn dust , B.H.C can be used in small areas.

o CaCN may be applied in 10 cm deep furrows between rows of seedlings at the rate of 70 g per sq. m.

o Grubs are killed by spreading nepthaleine crystals on moist soil at the rate of 2.7 g per sq. m.

o Aldrin dust and B.H.C can control the grub by applying 32 g per sq. m. mixed with soil at the time of seedbed preparation.

to adjacent healthy trees through root contacts. Roots decay after the tree death, thus establishing disease center. Conks are produced deep in the infected stumps or at the base of recently killed trees under leaf litter.


l Trees attacked by F. annosus display typical root disease and crown symptoms. l The trees loose their needles beginning with the oldest and progressing to the

youngest.l The colour of the tree crown uniformly changes to yellow or red.l Presence of fungus fruit bodies at the base of infected trees (Fig. 35).

l Fungus produces white pocket rot in the wood.l Butt rot result loss of most valuable portion of tree due to decay in heartwood

and reduction in growth due to death of roots.l Decay in roots result in wind-throw of trees. Control Measures

Silvicultural control

l As the fungus is present on dead roots, complete removal of stumps and residual roots to eliminate the fungus is essential. Even a small infected root left behind on the site may initiate new infection.

l The attack can be reduced by raising mixed plantation and introduction of root disease resistant species.

l Since the fungus is prevalent in moist and damp site, proper choice of suitable sites can minimize the fungus outbreak.

l The spread of the root disease under the soil can be prevented by making isola-tion trenches in between lines/rows of trees.

l Wider spacing and regular thinning may minimize the incidence of the fungus infestation.

Biological control

It includes introduction of non-pathogenic competitors like Peniophora gigantea. This can be done by inoculation of pine stumps with P. gigantea soon after felling, as it is a vigorous competitor with F. annosus. Chemical control

The root rot in freshly cut stumps can be minimized by surface application of chemi-cal (creosote, ammonium flouride, sodium nitrite, urea and ammonium sulphamate) in order to prevent stump colonization by the fungus.

Fig. 34. Witches broom formation on a tree as a result of Dwarf mistletoe infestation


Fig. 32. Fruiting bodies of Dwarf mistletoe

Fig. 31. A blue-pine branch infested by Dwarf mistletoe

CUTWORMS (Surface caterpillars)

Introduction

Cut worms or surface caterpillars are very injurious to natural and artificial regenera-tion and bring considerable damage in nurseries by cutting off seedlings at the ground

level. The damage is severe in conifers as they do not coppice.

Life cycle

The cutworm adults are moths belonging to Noctuidae family of Lepidoptera order. There are many species of cutworm moth larvae, some of which are not very damag-ing. But the majority of the cutworms affect seedlings at the early stages of growth. The adult moth lays eggs in the grass and weed piles. The larvae hatches out and feed on the weeds/grasses at the surface.

Damages

The most obvious damage resulting from cutworm is clipping of seedlings at the ground level.

Preventive Measures

l Keep the nursery beds clean through constant weeding. This is to prevent ovi-position and food sources of larvae.

l Loose soil should be compacted to prevent oviposition.l Avoid soil working during flight and oviposition period.

Control measures

l The larvae can be collected by hand and destroyed. l Leaves and weeds can be heaped for attraction of cutworms and destroyed

next day. l Cutworms can be killed by baiting with a mixture prepared of bran 2.5

parts, sodium fluoride 1/6 part dry and then in a mixture of molasses 1/4 part and water 4 parts by weight. The mixture spread at the rate of 2.25 kg per 100 sq. m. in the affected area after sunset.

l Flooding of nursery bed and hand collection is also an effective control measure.

l In the absence of poison, seedbeds may be dusted thickly with wood ash or a mixture of quick lime and ash as a repellent.

CRICKETS and GRASSHOPPERS

Dwarf mistletoe is the smallest dicotyledonous plant (Fig. 31 & 32) measuring less then 5 mm in length. It is a strong light demanding species and opening the canopy increases its vigour. The dwarf mistletoe has an explosive seed dispersal mechanism (Fig. 33). A single seed is thrown up to a distance of 25 to 30 meters. Seeds are sticky and adhere to any point of contact. Rain makes the sticky coating slick and seeds can slide within few centimeters on the host. Shoots emerge from the bark in 2 to 3 years and produce seeds in another 2 to 3 years. Individual shoots live 2 to 5 years, but the internal system lives as long as the host tissues. The inner root system absorbs moisture from the host and aerial shoots have a reproductive function.

Identification

Dwarf mistletoe appears as perennial shoots, either simple or branched. Length var-ies from few millimeters to few inches. They are found scattered or in groups along young twigs of the host. The jointed shoots have opposite pairs of scale-like leaves with varying colour from yellow to purple to brown to olive green. When shoots are shed, small basal cups often remain embedded in the bark, where young shoots again sprout in the following year.


l Bushy growth, thick branching habit and big bushy structures hanging on the trees.

l Witches broom formation on the infected branches are characteristics of this disease

(Fig. 34).l Presence of cankers, swellings and other branch and trunk abnormalities.l Tree form, health, size, height and diameter growth may be affected. l Attack by bark beetles on infested and weakened trees.

Preventive Measures

l Setting up natural and manmade barriers like roads, streams, meadows etc.l Clear-cutting the area before reforestation.l Leave uninfected seed trees or shelterwood when possible.l Removal of infested trees as far as possible.

Control Measures

l Sanitation felling of infested trees.l Complete removal and disposal of infected trees/stands is the best solution.l Pruning of infected branches and disposing them.

* Combination of several preventive and control measures provide the best solution in the management strate-gies of dwarf mistletoe.

ROOT & BUTT ROTFomes spp.

Introduction

Fomes annosus is distributed world-wide and is economically important and wide-spread in the temperate regions of the coun-try. It is sporadic and not of much concern

in the tropics and sub-tropical regions. The primary host of the fungus are conifers species, but few broad leaved species may be attacked as well. The disease sometimes causes serious damage to plantations of conifers.

Life History

Fomes annosus gets established in healthy conifer stands by infecting freshly cut stump surfaces by airborne spores. It then colonizes the stumps and root systems and spreads

Fig. 33. A magnified fruits of dwarf mistletoe with seeds


Fig. 7. Young conifer seedlings affected by Damping-off

Fig. 8. Conifer seedlings damaged by Damping-off disease

Fig. 29. Larva of Hyblaea puera feeding on teak leaf Fig. 30. Damaged leaves of teak by H. puera larva

Crickets and grasshoppers are other injurious pests of the nursery. They feed on young seedlings and shoots cutting them at night.

Control measures

l Freshly made tunnels of crickets are flooded with water or water mixed with kerosene. This will force the crickets to come out and they can be killed.

l Crickets can be trapped by sinking earthen pots or tins filled with water or water mixed with some kerosene.

l Half cut pumpkins are set as bait and covered with weeds in the evening. Crickets take shelter in these pumpkins and they can be killed next morn-ing.

l Grasshoppers are killed by hand-picking or setting baits. Young foliage can be controlled by spraying with 0.5 % aldrin, malathion.

IMPORTANT NURSERY DISEASESDAMPING-OFF

Introduction

Apart from pests, pathogenic and non-pathogenic diseases also occur in the nursery. Therefore, protection of seedlings from such diseases are essential. Among the patho-

genic diseases “damping -off” is the most serious of all nursery diseases. It is primarily a disease of conifer seedlings, but may attack broad-leaved species as well. The disease may sometimes destroy the entire nursery stock in one season, but may be unimport-ant in other years (Fig. 7 & 8). This disease is widespread across tropical, sub-tropical to temperate regions, where warm conditions favour the development of the disease. Causes of Damping-off

The disease is caused by a number of fungi which are normally soil saprophytes, but under favorable conditions for the development of fungi and unfavorable to the growth of seedlings, the fungi may become pathogenic. The important fungi that cause damping-off in seedlings belong to Pythium, Rhizoctonia, Phytophthora and Fusarium. Damping-off is favoured in clayey and wet soil, because of anaerobic conditions in

the rooting zones and relatively high temperature.


Mortality of seedlings occurs at 3 stages during their growth.

l The seedlings may be killed before they emerge above the ground level due to pre-emergence blight. The emerging crop is sparse. The losses due to such disease can be estimated by locating the killed seedlings in the soil while ger-mination is still in progress.

l The seedlings may be killed after emergence from ground level, as a result of rotting tissues at the base.

l The older seedlings may die due to root-rot underground. This is not too serious as the seedlings develop new roots if soil moisture conditions are favourable. But under severe drought condition, the seedlings may die altogether.

Control measures

conditions particularly temperature, and secondly by the food quality. Eggs are laid singly sticking to the lower side of young and tender leaves. A female can lay between 500 to 600 eggs. The incubation varies throughout the year from 2 to 4 days. The larval period varies from 8 to 26 days and pupal period from 4 to 25 days. The larvae are the most destructive feeding on young and old teak foliage. The adult moth undergoes hibernation from December to March.

The pest has several generations a year because of its short life cycle. E. mechaeralis has 10-14 overlapping generations annually and H. puera has 12-14 annual gen-erations. H. puera damages occur generally in April - May and again in November, whereas E. mechaeralis is abundant between April to early July and also in August and September.


l Complete defoliation of teak plants leaving only branches and stems.

l Causes dying back of shoots and forking of branches.l Development of epicormic branches if the plant is repeatedly attacked.

Control Measures

Since the life cycle is very short and infestation expected to be high, the pest must be controlled soon after observation. Never give time for the pest to build its popula-tion.

Silvicultural control

l Large pure teak plantations should not be raised.l Pure teak stands should be separated by strips or zones of natural forests.l The strips may further be strengthened by eradicating the food plants of the

pest by introducing certain desirable species.l There should be strict fire protection in the area.

Biological controlThe pest may be controlled by breeding and release of Cedria paradoxa. The fly is predator of the larvae of the pest.

Chemical controlAs the pest has quick succession of generations covering up to 14 generations annu-ally, it is not very economical to use chemicals for controlling the pest. Some chemical sprays may only be recommended in nurseries and small scale plantations.

IMPORTANT FOREST DISEASESDWARF MISTLETOE

Arceuthobium minutissimum.

Introduction

Dwarf mistletoe are parasitic plants of conifer trees. In Bhutan two species of dwarf mistletoe are found infecting conifer species on drier sites. Arceuthobium minutissimum attacks blue pine (Pinus wallichiana) and A. pini var. sichuanense attacks matured spruce (Picea spinulosa) trees. The infestation creates favourable conditions for the attack by other diseases and bark-beetle. The disease is widespread in the conifer growing regions of Haa, Thimphu and Paro.

Economic Importance

Out of 26.5 % of conifer forest in Bhutan, 12.1 % comprises of mixed conifer and 3.2 % of blue pine forest. The forests produce the major commercial timber for utilization within the country. Such forest must be protected from this disease for sustainable supply of timber in the long run.

Life history


Fig.9. Frost damage kills young buds and needles in the upper crown of the tree

Important forest pests and diseases with control measures Important forest pests and diseases with control measures

l Locate the nursery in a well drained site with light-textured soil and with no shade. If the nursery is raised in heavy-textured soil, sand should be mixed to increase porosity and drainage.

l The seed and soil can be treated with fungicides before and after sowing. This give effective control of damping-off and other seed-borne diseases.

l As damping-off is heavy in wet soil, watering must be kept at a minimum during early stages of seedling development.

l The disease can be prevented by partial sterilization of the soil by steam or fumigants.

l The soil can be sterilized with chemicals like formalin and methyl bro-mide. The chemicals must be applied to the beds 10-15 days in advance of sowing by which time the toxic effects of chemicals are removed through volatilization.

l When methyl bromide is to be used, the seedbed is first covered with thick polythene sheets with edges buried in the soil. The methyl bromide is broken under the sheet which is put back in position. The methyl bro-mide diffuses into the soil. The chemicals useful side effects are to control weeds, nematodes and insects.

l 250 ml of commercial grade formalin is diluted with 4 lits. water as rec-ommended by Bakshi (8) for 1 sq. m. of bed.

l Use of proprietary chemicals such as Captan (24.5 g per sq. m); Thiride (26.9 g per sq. m) and Cuman (26.9g per sq. m) can sometimes effectively control the disease. Such chemicals are broadcasted and forked into top 15 cm of soil one day prior to sowing.

* pH range between 4.5 to 5.5 is considered suitable to prevent serious damping off disease and maintain nutrient balance. Therefore application of calcium containing fertilizers or liming is not necessary.

* Soil treatment with chemicals is the most effective control measure to pro-tect conifer seedlings against damping-off.

FROST INJURY

Introduction

Frost injury is an abiotic damage caused by adverse climatic conditions. It usually occurs due to lowering of temperature of the air below freezing point. Frost is experi-enced in many parts of the country during the cold winter season from November to early March. Frost can be of three types: radiation frost, pool forst and advective frost. Radiation frost is most damaging to young plants. All conifers and some of the

broad-leaved species are prone to frost injury especially to nursery seedlings.

Symptoms

• Depending on the stage of development of the shoots at the time of the frost, buds which are breaking dormancy, needles of new growth and succulent shoots may be killed (Fig. 9).

• Frost damaged foliage and shoots become limp and begin to fade to yellow. After a week or more, the foliage is red resulting in dead shoots.

• Dead buds become dark brown in the interior.

Damages• New shoots or needles of breaking buds are

killed.• Growth may be stunted and tree form damaged.

The branches become bushy when terminal buds are killed.

• Young plants and their parts are completely killed due to frost lifting.

• Frost can cause cracks in mature plants.• Formation of canker which latter become

favourable point of attack by fungi and other

pathogens.

Preventive Measures

In Nursery• The nursery should be situated on northern or north eastern aspect.• Seed sowing should not take place too early and seed beds may be adequate-

ly covered.• In conditions of extreme frost, smoke may be produced at night to prevent

the damage.• The nursery beds should be shaded at night. The shade should be slanting so

d) Use of Pesticides

Some form of pesticides can also be used in controlling the population of bark beetles. The pesticides cannot penetrate deep into the bark, but have to be applied before the new bark beetles leave the host or logs to attack next green trees. The beetles get poisoned and die while leaving the tree. The advantage of this method is that no de-barking is needed.

As the application of pesticides is not environmentally acceptable, its use is very limited. The use may only be recommended, when there is no other option and the chemical has the least effect on the environment.

e) Integrated Methods

This method combine the use of trap log system, pheromones and pesticide applica-tion on a single control venture of the beetles. * Control measures b, c, d and e need prior approval of Director, DFS.

TEAK DEFOLIATORHyblaea puera

(Lepidoptera : Hyblaeidae)

Introduction

Teak (Tectona grandis) is a very important commercial timber. It is grown in a narrow belt of the southern part of Bhutan covering places like Phuntsholing, Samtse, Sibsoo, Sarpang, Gaylegphug, S/Jongkhar and Royal Manas National Park. Teak protection in these areas are given priority from felling and sale.

Teak forests are often attacked by two defoliators viz. Hyblaea puera popularly known as teak defoliator and Eutectona machaeralis known as teak skeletonizer. H. puera causes defoliation during growth period feeding on young and tender leaves (Fig. 29 & 30). and E. mechaeralis in the latter growing season feeding on older leaves. H. puera causes significant impact on tree growth, as compared to E. mechaeralis whose damage has very little effect on growth. Therefore, protection works should concen-trate on H. puera.

Economic Importance

The control of the pest is important, as the country has very limited area of teak forest. The epidemic outbreak of such pest can destroy the teak forest in no time.

Life cycle

Hyblaea puera undergoes complete metamorphisis in its development. The length of each of the several stages in the life cycle is determined primarily by the climatic


Fig.10. Adults of Ambrosia beetles

Fig. 26. Discolouration of conifer needles as result of bark-beetle attack

Fig. 27. Saw dust produced by bark-beetle at the base of an attacked tree

Fig. 28. Mother and larva gallery of bark-beetle in sapwood

Important forest pests and diseases with control measuresImportant forest Insect pests and diseases with control measures Important forest pests and diseases with control measuresImportant forest pests and diseases with control measures

that morning sun does not fall on seedlings. Shades are removed after the soil temperature has risen sufficiently.

In Plantation• Raise nurse crop which are not too dense.• Leave frost protection shelterwood or raise it artificially.• No weeding during winter months as the weeds protect plants against frost.

IMPORTANT FOREST PESTSAMBROSIA-BEETLES, PINHOLE and SHOTHOLE BORERS

Xyleborus spp.(Coleoptera : Scolytidae and Platypodidae)

Introduction

The genus Xyleborus is the largest in the family of Scolytidae. There are over hundred species of ambrosia-beetle inhabiting all parts of the world, where trees grow. Over 140 species of the Xyleborus have been discovered. These beetles are widespread from

very low to high altitude. It is an important pests of over 100 species of commercial timber. Other ambrosia beetles (Fig. 10) of the Scolytidae family include the genus like Pityogenes, Polygraphus, Scolytus and Trypodendron.

Platypodidae is another family of borers of similar habits. They live exclusively in the wood of trees. The genera that are important to foresters include Diacavus, Diapus and Platypus. Each of these genus has a wide range of species with many alternative hosts.

The groups of scolytid beetles live only in dead or weak trees. No species dwells in living parts of a plant as a regular habit. The ambrosia-beetles cultivate ambrosia fungus for food in the gallery-systems in the cambium stratum between the bark and sapwood. The main food of the beetle and larva is the mycelium and fructifications of the fungus grown on the wall of the galleries. They browse frequently on the dense cushion and hummocks of the fungus to keep the gallery passage open.

Economic Importance

Timber attacked by borers shows defects in the form of pinholes or black spots and lines on sawn timber surfaces. Sometimes the sapwood portion is severely weakened for the timber to be used for any purposes. Out of the many species of ambrosia-beetle, the most important to forest-ers are those that can multiply in accumulated wood refuse. Also, many of the freshly felled, converted and stored timbers are host to many species of these beetles.

Life cycle

The life cycle of the adult varies from few hours to 2 weeks or more depending on weather condition. Sometimes the colonies breed continuously over a year inside wood before emerging. The male do not bore tunnels and in most cases they have no other function apart from mating. Females bore through the bark and straight into the wood tissues and construct compound galleries (Fig. 11). They cut niches in series above and below these tunnels to lay eggs. Larvae develop in these cradles within few weeks, than pupate. New adults emerge from June to Sept. and most hibernate under leaf and wood-refuse. There is one or two generation a year depending on species.


Preventive Measures

• Immediate removal of wind-thrown, suppressed, dead, diseased, weak, broken and hanging spruce/blue pine trees to reduce source of infestation.

• Proper debarking of logs, stumps, lops and tops and branches upto 10 cm dia.• Regular patrol for detecting attacked trees.

Control Measures

a) Sanitation measures

• Felling, debarking and crosscutting of attacked trees should be organized im-mediately.

• If the attacked logs harbour adult beetle gunny bags or tarpaulins should be spread below the logs before debarking to prevent beetles from escaping.

• All bark, wood dust and beetles collected are burnt in case there are adult beetles.

• If larvae are found in the bark, they should be exposed to sun heat for killing. • Debarking of all fresh timber from stump to lops and tops upto 10 cm dia. should

be done.• Initial marking should be guided by an experienced forester to identify affected

trees.• Freshly attacked trees should be removed on priority basis.

b) Use of trap log system

• A sound host tree for the beetle is felled and cut into logs after debranching.• The stumps, lops and tops and any cracked part of the tree are debarked to

prevent breeding of beetles.• The logs with bark intact can be covered with branches to avoid surface drought

and to improve attractiveness.• The trap logs should be placed at a distance of 5 to 10 meters from the standing

host tree.• The logs must be numbered and registered to monitor the attack of beetles.• The logs are debarked when they are fully attacked and larva development

starts.• Trap logs should be debarked before larvae turns into pupae.• White larvae should be exposed to sun heat. Then burning of bark is not neces-

sary.

c) Use of Pheromones and Pesticidesd) Insect pheromones are chemical substances which the insects use to attract their partners for aggregation, mating and to invade the host. Artificial pheromones are produced to attract insects in this way. Bark beetles can be trapped in large numbers and later destroyed.


Fig.12. Dust produced by Ambrosia beetles as a result of boring activity

Fig.13. Entrance point of adult Ambrosia beetles

Fig.11. Wood damage and gallery systems of Ambrosia beetles

pith

bark

cambium

sapwood

heartwood

Fig. 14. Anatomy of wood

Fig. 24. The life cycle of Ips schmutzenhoferi

declivitylarva pupa adult

Fig. 25. Graph showing the generations and breeding flight in Bark-beetle

ca bd

Important forest pests and diseases with control measures Important forest pests and diseases with control measures Important forest pests and diseases with control measures Important forest pests and diseases with control measures

• Entrance points (pinholes) are marked by piles of fine white dust (Fig. 12). • Holes or galleries are surrounded by a dark brown or black fungus stain.• Tunnels in brood chambers branch in a horizontal place and cut across the grain

of wood.• Small diameter holes are bored into trees perpendicular to the bole (Fig. 13).

• Attacks weak, dying, recently cut trees or timber in storage.• Galleries within sapwood cause defect in logs (Fig.14).• Some species extend galleries into the heartwood and

freshly felled timbers may be attacked before drying.Preventive Measures

• Felling should be done during the dry seasons when beetles are hiber-nating and felled timbers should be stored in proper depots.

• Wood-refuse are collected and ex-posed to hot sun and burnt to prevent from breeding.

• Trimming and crosscutting of logs should be done just before dragging as retention of bark reduces attack.

• Store timber in deep shade or in water or end of logs coated with anti-splitting compounds (Chlori-nated naphthalene wax, Pentachlor-phenol).

• Squaring of logs of many species decreases the attack due to exposure of heartwood.

• Proper seasoning of converted tim-ber to 50 % moisture content can reduce pinhole attack.

• Use of repellents like mud, cow dung, tar, spraying with oil, dust, water soluble salts etc. to deter pinhole-borers attack.

Control Measures

• For already attacked timber the affect can be reduced by accelerated drying out by sun heating or kiln seasoning or steaming.

CHAMP DEFOLIATORUrostylis punctigera

(Hemiptera : Urostylidae)

Introduction

The champ bug Urostylis punctigera feeds on plants of Magnoliaceae like Magnolia pterocarpus, Magnolia insignis, Michelia champaca and M. excelsa. The pest is very destructive to pure stands of M. champaca. The damage is frequently very localized and infested areas do not spread rapidly from year to year.

Economical Importance.

In Bhutan champs species are widespread and are an important associate of the sub-tropical forest. Champ species are important commercial timber, which has high de-

Economic Importance

The study of the bark beetle is of great importance to forestry, as epidemic of the beetles create perennial problem for forest management particularly in mixed conifer-ous forests. Therefore, it is important for the foresters to have good knowledge on the beetle in order to save conifer species from destruction.

Life cycle

The bark beetles have four stages of development during their life (egg - larva - pupa and adult). Three stages of the insect (egg, larva, pupa) (Fig. 24) are found under the bark, where they are protected from adverse climatic conditions. The tunnel boring and egg laying starts in mid-April. The eggs are small and shiny white and are inserted into the sides of the tunnel. The larvae hatch out in May. The larvae are white, wrinkled, plump little grubs (3 mm) with distinct heads and no legs and usually curved into “C-shaped” posture (Fig. 24 a). They are found in the galleries that diverge from the mother galleries. They create their own tunnel by feeding on the cambium and sapwood.

The larvae develop into full pupa after 4 to 6 weeks. The pupae are white and naked and one can see the adult features forming, such as the eyes, legs, antennae and wings (Fig. 24 b). Pupae are found at the end of the larval gallery.

The pupa turns into a young, yellowish beetle after two weeks. The young beetle starts feeding between the galleries completely destroying the galleries. It becomes full adult in early July (Fig. 24 c). It takes about 10 to 12 weeks to become a matured adult before the beetle can take flight to detect a new host. The adult beetles starts emerging in April when the temperature is more than 18 ° C. The adult beetle is small, oblong insect of 5 - 6 mm length, brown to black in colour with cylindrical little teeth at the anterior portion of the back, which is known as declivity (Fig. 24 d).

The bark beetle has 2 generations per year with 2 sister breeding (Fig. 25). The du-ration of first generation is from mid April to mid July and second generation from mid July to mid September. The beetles over winter from October to March in the attacked trees. The adult beetles of the second generation fly from mid April, the fol-lowing year, when the temperature rises above 18 º C.

Causes of Infestation

• Predisposing factors of infestation are wind, drought and forest fires that creates favourable conditions for breeding.

• Leaving logs, lops & tops, stumps, branches and other wood-refuse after harvest-ing operation is by far the most dangerous source of infestation by the beetle.


• The green tree changes colour of the needles (gray, yellow brown or red) (Fig. 26).

• There is flow of resin from the attack hole.• Saw dust seen on the bark, at the base of the trunk and on surrounding bushes

and weeds (Fig. 27). • Falling of needles from attacked trees.• Formation of galleries or tunnels inside the bark and on cambium or sapwood

portion (Fig. 28). • Presence of eggs/larvae/pupa/adult (depending on season) under bark and

outside trunk confirm infestation by the beetle.• Woodpeckers feed on larvae/pupa/adult beetle.


Fig.15. Adult bug of Urostylis punctigera

Important forest pests and diseases with control measures Important forest pests and diseases with control measuresImportant forest pests and diseases with control measuresImportant forest pests and diseases with control measures

Fig.16. Badly defoliated champ leaves by U. punctigera

mand and value. Foresters should therefore have a sound knowledge on its protection measures before any epidemic outbreak of the pest.

Life cycle

The pest has 5 generations a year with the life cycle lasting from 30 to 60 days per generation depending on weather conditions. Oviposition begins 4 or 5 days after emergence. Eggs are laid on young leaves in 2 parallel rows in a glutinous yellow secretion. Each egg-mass contains 15-30 eggs (average 19). One female may lay 450 eggs (average 250) in 30 separate egg masses. Oviposition ranges between 1 to 3 weeks sometimes extending to 5 weeks. The first instar nymph is not mobile and remains in the egg mass for 1-5 days without feeding until the first skin is moulted. The nymph undergoes 5 successive nymphal stages before maturing.

The nymphs suck the sap of newly formed leaves and shoots and later feed exclusively on old leaves. The 4th and 5th instar nymphs are capable of feeding on petioles, soft and older shoots as they are unable to pierce hard bark. The early stages of attack are confined to the terminal foliage, leading shoots and uppermost branches of a tree. As the nymphs grow older and the new growth of plant is exhausted they converge towards the thicker part of the shoots and main stem and concentrate near the whorls of shoots and round the stem. The adult (Fig. 15) is able to cause more damage than nymphs because of its size and longer life span.

Symptoms

• The infested leaves have several holes, wilts and wrinkle (Fig. 16). • Old leaves show brown spots 1 to 3 days after puncturing. Brown spots appear

first on lower surface and slowly spread to the upper surface, which ultimately turns white except the edge.

• Attacked leaves have the smell of bug.

• The leaves that are severely attacked turns yellow and fall.

• The attacked shoots show brown patches and bands just below the epidermis.

Damages

• Defoliation of young and old leaves including soft shoots.• Mass attack results in loosing leader and lateral branches and die

back at ground level. • Older trees have the crown and uppermost portion killed to a length

of 15 feet from top or to a diameter of 3 inches.

Control Measures

• Young plantation should be regularly inspected in order to discover incidence of bug.

• Protection should be concentrated on early stages of nymphs clustered on young leaves.

• Produce smoke by burning thatch grass or straw or cow dung. When the smoke reaches the young nymphs, the bug start falling to the ground.

• The best way of preventing damage by the nymphs is shaking the infested portion.

• In order to protect tree from re-ascending by the nymphs, circular band of sticky sub-stance or grease or fresh cow dung can be applied.

CHIR DEFOLIATOR

Labeda nobilis(Lepidoptera : Lasiocampidae)

Introduction

Labeda nobilis is a defoliator of chirpine (Pinus roxburghii) trees. The insect has other alternate host species like the Myrica rubra, Quercus and Thysanolaena agrostis. In Bhutan chir forest comprises of about 2.5 % of the forest area. Therefore, this pest is mainly localized in the chir growing regions of the warm sub-tropical forest types. Major damages were reported from chir growing areas of Wangdue, Trashigang and Mongar districts.

Economic Importance

Since chir is one of the important local and commercial timber of the sub-tropical regions of the country, it is essential for the foresters to have some knowledge of this

Life cycle

Adult moths are nocturnal hiding during day and emerging in the early evening. Eggs are laid during night on young leaves, usually one egg per leaf. A female can lay upto 400 eggs. The larvae emerges within 24 hours after egg hatching. Oviposition lasts for 6 days. The larva (caterpillar) hatches in 1 to 5 days. It feeds on the lower epidermis and inner tissues leaving upper epidermis intact. The matured caterpillars consume the whole leaf and avoid matured leaves. When disturbed the caterpillar drops at the end of a silk thread. It can travel rapidly over the soil and plants and reascend a tree.

The larval period varies with temperature from 10 days in hot weather to 13 days in spring and 20 days or more in autumn. The larva undergoes 5 moults. Pupation takes place on the ground among leaves or debris or in loose soil. The pupal period lasts 5 to 7 days in hot weather and 8 to 11 days in autumn. Hibernation occurs in pupal stage lasting for 80 to 100 days. There are as many as 10 to 13 generations annually with a life cycle varying from 17 to 32 days, depending on weather conditions of the place.


• Mostly the young leaves are defoliated .• The female moth lays one egg per tender leaf.• When the caterpillars are disturbed they drop at the end of silken thread.• When foliage is completely destroyed, large armies of caterpillars may be seen

moving over the ground in search of a fresh host.• The growth of plants is hampered to a large extent due to defoliation.• Repeated or persistent attack may lead to the death of the tree.

Preventive and Control Measures

Combined silvicultural and biological practice provides the most effective control of the pest.

Silvicultural measures

• Shisham should be only raised where soil condition is good with sufficient moisture.

• Raising methods should be adopted that trees produce flush of young leaves before the caterpillars are hatched, as caterpillars feed on young and succulent leaves.

• Early thinning operations in plantations are desirable.

Biological measures

• The insect pest has many enemy parasites. The pest population can be controlled by release of Disophrys sissoo and Microgaster plecopterae.

SPRUCE BARK BEETLE (Ips schmutzenhoferi)

(Coleoptera: Scolytidae)

Introduction

Bark-beetles are particularly destructive pests with rather remarkable living habits. They belong to the beetle Scolytidae and represented as many as over 600 species. But we are primarily concerned with one of the most destructive species that has caused extensive damage to spruce (Picea spinulosa) and blue pine (Pinus wallichiana) forests.

In Bhutan two species of bark beetles are discovered viz. Ips schmutzenhoferi and Ips longifolia. These two beetles have great economical importance to Bhutan forest. The former is confined to spruce and blue pine the latter on to chirpine (Pinus roxburghii). Ips schmutzenhoferi is the most destructive among the two beetles damaging large areas of spruce forest. A great deal of studies on the biology, life cycle, behavior and control measures were conducted by H. Schmutzenhofer and D. B Chheteri, where plenty of information is available in their field reports. (Schmutzenhofer and Chhetri, 1996, Schmutzenhofer 1985, 1988, 9189) Past History

In Bhutan, major infestation by Ips schmutzenhoferi on natural stand of spruce and blue pine were reported from the western and central part of the country during 1985-89. It was noticed that this beetle even attacked larix tree (Larix grifithii) when the popula-tion reached beyond epidemic proportion. The epidemic level is extended mainly at altitudes between 2,800 - 3,300 meters.


Fig. 17. The life cycle of Labeda nobilis

Fig. 18. Matured larva of L. nobilis with dense pubescence

Fig. 23. Frass at the base of sal tree due to boring activity of H. spinicornis

2330Important forest pests and diseases with control measuresImportant forest pests and diseases with control measures Important forest pests and diseases with control measures Important forest pests and diseases with control measures

pest. A single outbreak of the pest can cause severe damage to chir trees, as chir is usually grown as pure stand crop.

Life cycle

Eggs are laid by the females on pine needles after fertilization (Fig. 17). The caterpil-lars are about 4 inches in length when full grown. The body is covered by a dense pubescence and tufts of erect hairs (Fig. 18). Pupation lasts for 2 - 3 weeks and takes place in the undergrowth or rolled up leaves in a tough cocoon. The moth emerges in August. There is one generation a year.


• Attacked trees have very less or no needles.• Trees look totally dead when they are severely defoliated.• Hairy caterpillars can be seen crawling down or climbing up on the tree trunk

and branches and even on the ground.

• Lot of fallen needles on the ground.• The sound of falling larval droppings.• Attack can be noticed in the form

of a patches. • Cocoons can be noticed on the

ground as well as on branches in later stage.

• Eggs can be noticed in the needles during cold periods.

Preventive Measures

• Strict fire protection in order to promote biotic control.

• Promote regeneration of broad leaved spe-cies to avoid pure chirpine stands.

Control Measures

Mechanical• Collection of caterpillars and cocoons is

the simplest remedy in case of small area

plantations.• Trapping of the moths at night.

Natural Control • The caterpillars are attacked by Nucleopolyhedrosis virus and their population

is reduced to a great extent.• The caterpillars are voracious feeder and many suffer and die due to lack of

sufficient food at the time of mass outbreak.

GAMHAR DEFOLIATORCalopepla leayana

(Coleoptera : Chrysomelidae)

Introduction

Calopepla leayana is a serious pest of gamhar (Gmelina arborea). This pest is more severe and prevalent in pure plantation of gamhar. Defoliation starts with the advent of rain and continue till the end of the rainy season in many places.

Economic Importance

The adult beetles and larvae of all stages feed entirely on leaves of Gmelina arborea completely defoliating the plant leaving only the midrib and main veins of the leaf. The heavy attack on the plant causes the leading shoots of young trees to dry up and trees remain leafless for most of the growing season. Under such conditions the trees should be given protection from the massive outbreak of the defoliators.

and magnitude of the operations.

Control measures

• The attacked trees should be felled and debarked to expose the larvae to predators.

• In case of severe infestation of beetles in the forests, 1 trap log per hectare may be provided in the affected area. The beetles are attracted by the freshly oozing sap and get intoxicated by drinking the sap. The beetles are then collected by labourers before sunrise everyday and killed by dropping in kerosene oil. The trap logs should be disposed off after completion of trapping operations.

• The infested logs if not splitted to expose larvae should be taken at least 5 Km away from the sal forest.

• The population of the borers can be biologically controlled by raising and release of parasites like Ichneumon and Bothrideres fly. The grubs of these flies are either external or internal parasites of the larvae of Hoplocerambyx.

* (Trap log method: A log is cut from a freshly felled tree. The bark of one end of the log is smashed 1-2 feet in length to produce sap that can attract the beetles. When the beetle catch lowers, additional bark is smashed 1-2 feet from the earlier smashed end. It is continued till the entire log is completed. If beetles persist in the area, start with a new trap log. Do not forget to check for beetles in the logs which are felled, but not used as trap log.)

SISSOO DEFOLIATORPlecoptera reflexa

(Lepidoptera : Noctuidae)

Introduction

Plecoptera reflexa is an important pest of shisham (Dalbergia sissoo), which is another important commercial timber. The pest also attacks Dalbergia latifolia and Pterocarpus marsupium. These plants suffer from severe defoliation and sometimes the tree is made leafless affecting growth and often killing the tree. The attack by the pest is very severe in irrigated plantations of sissoo.

In Bhutan epidemic outbreak of the pest is reported from Sarpang Division. Due consideration should be given to safeguard this tree species as the kingdom has very limited natural stand of sissoo forest. Most sissoo forest are created through plantation.

Economic Importance

P. reflexa rarely occurs in abundance to destroy the foliage in natural stands of pure shisham. The destruction is more serious in plantation, roadside and avenue trees. The cumulative effect of defoliation is very disastrous. Trees remain leafless for the greater part of the growing season and repeated attacks result in dying of tips and leading shoots. A crop of epicormic branches is produced and ultimately the tree succumbs to the attack.

Female

Male

Cocoon

Caterpillar

Egg


Fig. 19. Adults of gamhar defoliator Calopepla leayana

Fig. 21. The Developmental stages of Sal borer Hoplocerambyx spinicornis

Fig. 22. Adult sal borer (Hoplocerambyx spinicornis)

24 252829 Important forest pests and diseases with control measures Important forest pests and diseases with control measuresImportant forest pests and diseases with control measures Important forest pests and diseases with control measuresLife cycle

The eggs are yellow and elongated and laid vertically in clusters of 10 to 100 (aver-age of 60). It is embedded in a frothy secretion that hardens to form the ootheca. The ootheca are placed on the under surface of leaves or on shoots. The oviposition period extends to six weeks. Each female lays about 23 egg masses. The life span of the beetle (Fig. 19) is about 50 days (maximum of 120 days) in the first generation and six to eight months for the over wintering generation.

The larva has five instars. The colour of the larva changes from primrose to yellow in the first instar to pure black in the 5th instar. The most distinctive characteristics of the larva is the bunch of long, fine and black filaments attached to the anal end. When disturbed the larva flick these filaments up and down in a defensive or frightening ac-tion. The matured larva pupates on a leaf fastening itself by the first three abdominal segments. The average life cycle of the beetle is approximately 35 to 50 days. There are 2 to 3 generations a year depending on the locality.


• Defoliation is first noticed on the onset of the rainy season.• Large circular holes are present on the leaves resulting from feeding by larva.• Damage of young buds and shoots due to feeding by larva.• Complete skeletonisation of leaf leaving only midribs and main veins by 4th

and 5th instar larvae.• Heavy attack causes the leading shoots of young trees to dry up and remain

leafless.

Control Measures

Silvicultural• G. arborea should be planted only

on suitable sites.• Pure plantation of G. arborea should

be divided into strips to provide more light.

Mechanical• Beetles hibernating in shelters (e.g. under bark, cracks, hollows) can be col-

lected by hand and destroyed. This can be facilitated by destroying the natural

shelters to force the beetles to congregate on the few remaining shelters. • The beetles can be trapped by white surfaces using a large sheet of white cloth

or metal having a central funnel or bag.

Chemical• Under severe infestation the foliage along the edges of plantations are sprayed

or dusted during the migration of beetles.

INDIAN GYPSY MOTH Lymantria obfuscata

(Lepidoptera : Lymantridae)

Introduction

Many species of this family feed on forest trees and several are notorious pests of temperate regions. Lymantria obfuscata is the main pest of Quercus spp, but has other host species like Alnus, Walnut, Rhododendron, Schima wallichii, Salix alba and Salix fragalis. It also attacks some of the cultivated fruits like apricot and apple. In Bhutan this pest is confined to cool broad-leaved forests of pure oak and temperate forest where oak is grown as associate species. The epidemic occurrence of the pest was first reported in 1993 from Luntse and Trashiyangtse area.

Economic Importance

Oak is one of the most important species in temperate regions. Since this species is commercially important, the epidemic outbreak of the pest should be controlled to save the species.

the trunk and branches of standing trees. The larvae hatches out when the temperature is 28 ºC and humidity is 91 %. The normal incubation period varies from 5 to 8 days. The larva after hatching spends whole life in the wood by boring into bark, cambium, sapwood and finally into heartwood. The larva starts pupation in the pupal chamber 2.5 to 3 inches from sapwood.

The adult (Fig.22) on assuming beetle form remains in a resting condition in the pupal chamber. It then breaks the calcareous covering, closing mouth of pupal chamber and find its way out through the broad larval tunnel. Sometimes it gnaws the way through the mass of wood refuse (in the larval galleries) and bark to come out. It is full grown beetle by May - June and waits for emergence until monsoon arrives. In each monsoon showers, fresh lot of beetles emerge.

The beetles leave the tree at night. The beetles are active particularly during the warm-est part of the day or on a cloudy, dull and rainy days. They avoid direct sunshine by sheltering in shady places, but readily take to flight when the sky is overcast and driz-zling. After sunset the beetles rest in sheltered places under logs, crevices and flakes of bark and large leaves.

Economic Importance

Sal is one of the important timber of the sub-tropical region of Bhutan. The sal forest cover only limited areas, which is mostly plantation forest. Therefore, the forest must be protected for future use. As sal trees are often infested by these beetles, the foresters should have a greater knowledge on the life cycle and control measures of this pest.

Symptoms

• The trees pour out masses of resin at the points where the grubs are working inside the bark. These masses coagulate on the tree and are visible.

• Attacked trees have reddish or yellowish coloured crown.• Old attacked trees usually have completely dead top, but lower branches are

still green.• In freshly attacked trees lots of frass at the base of the trunk and undergrowth

is visible (Fig. 23). • Presence of larvae in the cambium layer if the freshly attacked tree is debarked.

• Presence of tunnels like holes of larva in the sapwood.• Matured larva in the tunnels of sapwood/heartwood when tree is split.• Dark colour of wood dust indicate that the larva has penetrated into the heart-

wood.• A large number of woodpeckers holes on tree due to feeding on the larvae.

Damages

• The larva kills the tree by girdling during the course of mining galleries in the cambium layer.

• It bores long galleries in sapwood and heart-wood and thus greatly reduces the strength and value of timber.

Preventive measures

• Regular patrols must be carried out to check borer infestation.

• The felled or wind-fallen or infested stand-ing timber should be debarked and disposed immediately to prevent breeding of borers.

• Sal plantation should be thinned from time to time to reduce over stocking and to increase the vigor of the stock.

• Remove dead, weak, suppressed, damaged and disease trees for improving the future growing stock and to prevent breeding of borer.

• The most effective protection is to undertake felling during October to March when the borers are not on wings and are not laying eggs.

• Debark all logs, stumps, big branch wood, butts, forks, off-cuts, slabs etc. up to 8 inches diameter that is left in forest after felling.

Remedial measures

Since the area of sal forest is very limited in the country, total enumeration of the at-tacked trees should be carried out to ascertain information on the incidence, outbreak


Fig. 20. The life cycle of oak defoliator Lymantria obfuscata

26 27Important forest pests and diseases with control measuresImportant forest pests and diseases with control measures

Life cycle

The females lay the eggs as soon as it is fertilized by the male. Females cannot fly much due to the feeble wings and bulky body (Fig. 20). The eggs are laid close to the pupation site in June/July. The caterpillar hatches in March/April and feeds for 6 weeks. The larva undergoes 5 instars and average feeding days is calculated to be 48.5 days. The pupal period lasts for 10 to 14 days and emergence of moth occurs during June/July of the following year. The hibernation take splace while the insect is in its pupal stage. The females die as soon as the ovaries are empty. The insect remains in the egg stage for 297 days on average. The life cycle is completed in one year. Thus, there is only one generation a year.


The larvae feed on the young and matured foliage of the host tree and the infected area shows the characteristics of a burnt forest.

Control Measures

The G ypsy moth is always present in the nature and their population is regulated by the natural enemies like the predators, parasites and viral diseases. Nucleopolyhedral virus disease and Tachinidae parasites play a vital role in controlling the population of larvae and pupae of Lymantridae. The epidemic outbreak is followed by sudden disappearance of the pest.

SAL BORER (Hoplocerambyx spinicornis)(Coleoptera: Cerambycidae)

Introduction

Hoplocerambxy spinicornis is the most important and serious pest of Sal trees (Shorea robusta). This tree is of high eco-

nomic importance for commercial use due to its strength and durability. In Bhutan the pest is mostly prevalent in the sal forest of southern regions of Sarpang, Samtse and Samdrup-Jongkhar districts. In the recent years, major damages were reported from Sarpang and Samtse Division, although sporadic infestation is present in many of the sal growing areas. The control of this pest is of great concern to the foresters, as Bhutan has only a small stretch of sal plantation that must be protected for future generation.

Life cycle

The beetle undergoes complete metamorphisis during its development from egg-larva-pupa-adult (Fig. 21). The female begins to lay eggs 7 to 9 days after first fertilization and there after lays numerous eggs without a second fertilization. The maximum number of eggs laid by a single female is 468 and maximum oviposition period is 30 days. Eggs are laid singly and placed in the underside of logs on ground and shady side of

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