Welcome Dr.M.THIPpaiah

Professor (Entomology) College of Agriculture ,G. K.V.K

U.A.S , Bangalore-65

Types of damage to plants by different insect pests

Insects inflict injury to plants either directly or indirectly in their attempts to secure food and almost all portions viz., roots, stem,

bark, shoots, leaves, buds, flowers, and fruits of plants are attacked and damaged by insects

A Knowledge of the feeding habits of insects, Which fall in to two main groups

1. Chewing insects Theses insects cause direct effects and indirect effects2. Sucking insects

A. Direct effects of feedingI. Injury by chewing insects

Insects which chew off external plants parts , grind them up and shallow them and they possess biting type of mouth parts and cause damage as detailed below :

1. Feed on the growing points of plants causes retard growth Eg : Grape vine beetle – Scelodonta strigicollis

2. Feed on the leaves and defoliate the plants causing reduction in assimilative leaf area and thus hinder growthEg : 1.Semilooper caterpillar, Achaea janata on castor

2. Red headed hairy caterpillar, Amsacta albistriga on Ground nut

3. Slug caterpillar, Latoia lepida on Mango and Castor

3. Notch the edge of the leaves

Eg : 1. Ash weevil – Myllocerus sp. feeding on a variety of crops like Ragi, Moringa, Brinjal, Cotton etc.,

2. Grass hoppers - Hieroglyphus banian Feeding on maize Oxya spp.

4. Make small holes in the leaves by feeding

Eg : Flea beetle causes this type of damage on radish and Sunhemp

5. Feed on a layer of surface tissue of the leaves

Eg : Larvae of the diamond back moth, Plutella xystella on Cabbage and Cauliflower

Or feed superficially on the surface tissue

Eg : Grubs and adults of epilchna beetle, Henosepilachna vigitioctopunctata on Brinjal and Bitter gourd

6. Leaves with large holes of irregular shape and size due to feeding

Cut worm – Spodoptera litura on Sun flower

Soy bean semilooper, Thysanoplusia orichalcea

7. Roll up the leaves and feed within

Paddy leaf roller – Cnaphalocrocis medinalis

Cotton leaf roller- Sylepta derogota

8. The larvae feed on the bark of the plants or trees while beingconcealed in a protective covering like frass and excreta in a silken web

Eg : Bark eating caterpillar – Indarbela tetraonis on Mango, Moringa, Curry leaf , rain tree etc.,

9. Cut the stem of the tender plants at the time of germination

Eg : Surface weevil, Attactogaster finitimus attacks the seedlings of cotton raised under rainfed condition in black cotton soil

Cotton shoot attack by weevil

Eg :1. Adults of blister beetle – Zonabris pustulata on red gram and Sesbania

10. Feed on flower buds and flowers and cause reduced seed production

2. The larvae of spotted pod borer – Maruca vitrata web the flower buds and flowers on red gram and feed on them

3. Cetoniid beetles - on rose feed on the flower buds and petals

11. Nibble and cut off ear heads

Eg : Rice grass hoppers

12. Eat partially on the grains and give chaffy appearance

Eg : Damaged by the larvae of Helicoverpa armigera to the ear heads of Sorghum and Finger millet

II. Injury by piercing and sucking insects These insects remain out side and with their mouth parts pierce through the epidermis and suck the sap

The following symptoms or kinds of damage are caused by sucking insects by mode of feeding

Many of the sucking insects, at the time of feeding inject their salivary secretion which due to presence of toxins damage the plant tissues further.

1. Most of the sucking insects attack the leaves of plants A general chlorosis is caused by aphids and many of them cause ultimate withering and drying of the affected portions

Eg : 1. Cow pea aphids – Aphis craccivora on Lab-lab, Ground nut, and Gliricidia

2. Yellow speckling of leaves may be produced due feeding

Eg : Castor whitefly – Trialeurodes ricini

Coconut scale – Aspidiotus destructor

3. Silvering or whitening of leaf surface due to removal of cell contents below the epidermis Eg : Typical damage caused by thrips on paddy

2. White feeding spots on the leaves are caused by thrips on Onion

White spots on the upper surface of the leaves caused by Stephanitis typicus on coconut

4. Hopper burn or Necrotic brown lesion : Typical injury produced by leaf hoppers / plant hopper

Eg : 1. Brown plant hopper – Nilaparvatha lugens on rice

2. Cotton leaf hopper - Amrasca biguttula biguttula

3. Castor leaf hopper – Empoasca flavescens

5. Crinkling or curling of leaves is caused by insects like Aphids , Thrips and leaf hoppers – Eg : Thrips , Scirtothrips dorsalis on Chillies

6. Vitality of the plants gets reduced and premature dropping of leaves in case of Tomato whiteflies – Bemisia tabaci

Adults and nymphs suck the sap from twigs, branches and fruits

Plant -weak, low yielding, death

Fruits-grey mottled blemishes, reduces quality

7. Premature shedding of developing fruits or drying of shoots as in Scales and mealy bugs

Eg: Sanjose scale on Apple

8. Premature fall of fruits as in Citrus caused by the fruit sucking mothsEudicima phaloniaE. materna

III. Injury by Internal feedersThe internal feeders cause damage by remaining within the plant tissues during a part or all of their destructive stages

The internal feeders may be grouped as Borers Worms or Weevils Leaf miners Gall insects

1.BorersWhen the larvae feed on the wood or pith of the plant or part of the plant which may be generally large enough to contain the body of the pest , they are referred to as borers

Eg : Larvae may bore in to the terminal shoots and cause death of the shoots as in the case of cotton boll worm – Earias spp.

Rice stem borer : Scirpophaga incetulas – Larva enter in to the stem and cause death of the central shoots i.e dead heart symptoms

Soghum stem borer – Chilo partellus larvae enter into the stem and cause death of the central shoots i. e dead heart symptoms

The stalk borer, Papaipema nebris on soy bean

The larvae bore into flower buds cause shedding such larvae are usually called bud worms Eg : Jasmine bud worm

2. Worms and Weevils :

The larvae may bore into the bolls1. Cotton boll wormHelicoverpa armigera

Mango nut weevil, Sternochetus mangiferae feeding inside on the stone of the fruit

Larvae may bore in to the nuts

Brinjal fruit borerLeucinodes orbonalis

Larvae also bores in to the fruits feeds on inner contents

Castor capsule borer : Conogethes punctiferalis

3.Leaf minersLarvae live in between the two epidermal layers of the leaves and feed on internal content , they are referred as Leaf miners

Eg : 1. Citrus leaf miner – Phyllocnistis citrella

2. Cashew leaf miner – Acrocercops syngramma on Cashew

3. Serpentine leaf miner – Liriomyza trifolii on Tomato

4. Ground nut leaf miner – Aproaerema modicella

4. Gall insectsImmature and adult stages of certain insects are to be responsible for the formation of special plant deformities known as galls and these galls provide shelter and food to the insect

Eg : Psyllid galls, Cecidomyiid galls ,Aphid galls

Psyllid galls

Psyllid galls

IV. Injury by Subterranean Insects

Insects which are found in the soil live by feeding on the roots of plants and trees, by chewing or boring or sucking sap or Forming galls

Root grubs feeds on the roots of the plant

Root aphids feeds on roots of Ragi plants

V. Injury to Stored productsIn 3 ways the stored products are attacked by insects

1. It may be continuation of a field attack

In storageHatching larvae bores into the tubers make tunnels in the tubers and infested tubers may be completely riddled by silk lined burrows, filled with larval larval excrement

Field conditionLarvae mine in to the petiole as a result drooping symptoms and finally produces blotches on the leaves

Eg : Potato tuber moth Phthorimoea operculella

Eg: Sweet potato weevil – Cylas formicarius

The grubs bores in to stems of vines cause tunneling inside and feed on soft tissues

Grubs and adults bores into the tubers both in filed and storage gowdowns and affected tubers develop dark patches , which later start rotting

2. The eggs may be laid in the field itself and damage may occur in the storage

Some pulses are attacked by the Pulse beetle, Callosobruchus chinensis

3. The infestation may continue from the material stored earlier carried over to fresh material stored later in godown or storage house

Eg : Rice weevil - Sitophilus oryzae

Rice moth – Corcyra cephalonica on MaizeIt attacks broken grains and flours especially the milled products, which are heavily damaged if neglected

B. Indirect effects of feeding

1. Making the harvest more difficultHeavy incidence of some pests on crops makes the harvest of the crop more difficult

Eg : 1. Cabbage infested heavily with aphids

Red gram pods infested heavily with aphids and bugs

2. Kapas from cotton bolls damaged by pink boll worm

2. Causing contamination and loss of quality of the product

Due to insect attack the final produce may show loss of quality by reduction in nutritional value or marketability

1. Cardamom berries infested by thrips – Sciothrips cardamomi

2. Sweet potato tubers riddled with holes caused by - Sweet potato weevil – Cylas formicarius

3.Brinjal shoot and fruit borer Leucinodes orbonalis

4. Amaranthus leaves skeletonized by larvae of Hymenia recurvalis

5. Potato tuber moth - Phthorimoea operculella

6.Cabbage with shot holes by the semilooper – Trichoplusia ni

3. Disseminate plant diseasesInsects are responsible for spreading many plant diseases caused by Bacteria, Fungi and viruses

Eg : 1. Paddy leaf hoppers – Nephotettix spp. – transmit viral disease like Rice tungro virus

2. BPH – Nilaparvatha lugens – A vector of grassy stunt virus

3. Bunchy top of banana – Transmit by aphid , Pentalonia nigronervosa

4. Sterility mosaic virus of red gram transmit by Eriophyid mite, Aceria cajani

c. Injury by other methods 1. Injury by egg layingInsects takes a great deal of care in laying their eggs at the right place so that the young one will have enough food material for its development and thus survive

Cow bug, Oxyrachis tarandus

adults and nymphs attended by ants

Eg : Cow bugs insert their eggs into the plant tissue of the tender stem and thus cause injury

2. Use of plant parts for making nestsSome times parts of plant are removed by insects for the construction of their nests though they do not feed on them

Eg: 1. Leaf cutter bee, Megachila sp.

2. Tropical leaf cutting ants

2. Tropical leaf cutting ants

3. Red ants construct their nest

3. Injurious insects being carried from one plant to another

Ants and some other kinds of insects they are not injurious to crops by themselves , often carry the insects to other plants such injurious forms are aphids , mealy bugs etc;

Ants carry the aphids from one plant to the other plants

Red ants carry the mealy bugs from one plant to other plants

Thank you