MECHANISM OF RESISTANCE IN PLANT

AGAINST ORIENTATION, FEEDING AND OVIPOSITION

OF INSECT

Arvind KumarH-13-1-D

KM. Painter classified mechanisms of resistance into 3 main categories

Antixenosis (Non preference)

Antixenosis is mechanism employed by the plant to deter or reduce

colonization by insects. Plants that exhibit antixenotic resistance should

have a reduced initial number of colonies early in the season.

Antibiosis

Antibiosis operates after the insect have colonized and have started

utilizing the plant.

Tolerance

Tolerance of the plant does not affect the rate of population increase of

the target pest but does raise the threshold level.

Antixenosis

ANTIXENOSIS TO OVIPOSITION

Resistance to oviposition may come from plant characteristics

that either fall to provide appropriate oviposition-inducing

stimuli or provide ovipositional inhibiting stimuli.

Oviposition preference is discussed on two bases of the plant’s

1. biophysical and

2. biochemical traits

BIOPHYSICAL FACTORS

Plant pubescence

Frego bract

Visual factors

PLANT PUBESCENCEInsects with piercing and sucking mouth parts are deterred from feeding on hairy plants or vascular bundles.

Breeding of hairy cottons in Africa and Asia to combat the Jassids Empoasca spp. constitutes the foremost host plant resistance (HPR).

Pargell et al., (1949) demonstrated that greater hairiness to both upland cotton (Gossypium hirsutum) and Egyptian cotton (G. barbadense) mm related to jassid resistance.

Soybean varieties with a dense hairiness of foliage can manifest both antixenosis to oviposition and feeding deterrence against leafhoppers, The simple trichomes deter oviposition and feeding by preventing; the insect’s ovipositor or proboscis from reaching the plant epidermis(Lee 1983)

Pubescent wheat cultivar Vel exhibits antixenosis to adults andlarvae of the Hessian fly Mayetiola destructor (Roberts et al., 1979).

FREGO BRACT

Other morphological features of plants, such as frego bract in cotton,

help reduce the number of eggs laid and subsequent damage by boll

weevils Anthonomus grandis (Jenkins and Parrot 1971).

In field experiments, frego-bract cotton showed 50% less damage

from oviposition than normal cottons did. The role of the frego bract

in reducing damage by the boll weevil appears to be due to some

adverse effect on insect behavior.

Frego bract is associated with hypersensitivity to the plant bugs

Lygus spp. and cotton fleahopper Pseudatomoscelis seriatus (Jenkins

et al 1973).

VISUAL FACTORS The colour and shape of plants remotely affect host selection

behaviour of phytophagous insects and have been associated with

some resistance.

Ex: Specific color-related resistance, For example, the red and glossy

nature of Cruciferae plants was a major factor conferring antixenosis

resistance against the cabbage aphid Brevicoryne brassicae (Singh

and Bills 1993).

Yellow colour is preferred by aphids

Green and blue green is preferred by cabbage butterfly

Dark green preferred by rice leaf folder

BIOCHEMICAL FACTORS Chemical cues are involved in all the three phases of host

selection behavior; orientation, oviposition and feeding. Many

factors play a role in the process of opposition by different

insects, but long-range orientation of many insects to their host

plants is known to be guided by volatile, compounds emanating

from plants. Volatile hydrocarbons and other secondary

compounds act as oviposition deterrents

Onion volatile diallyl disulfide is antagonistic to onion fly

Delia antiqua..

ANTIXENOSIS TO FEEDING

Insects respond to various feeding stimuli when selecting their host plants.

The absence of such stimuli and the presence of deterrent compounds

presumably contribute to antixeniosis types of resistance. The plant surface

is embedded with physical and chemical factors responsible for antixenosis

to feeding insects (Southwood 1986).

number of phytophagous insect species shows that before feeding on a

plant they make some land of sensory exploration of the plant surface as a

prelude to biting. The leaf surface acts as the crucial interface between the

insect's battery of chemoreceptors and the plant (Southwood 1986

ANTIXENOSIS TO FEEDING

Nonglandular trichomes

Glandular trichomes

Leaf surface waxes

Thickness of cell well

Nutrient deficiency

NONGLANDULAR TRICHOMES Trichomes affect locomotion, attachment, shelter, feeding,

digestion and oviposition of insect and the effect depends on

density, length and shape of trichomes. Long hairs not only impede

movement, but also prevent the insect from reaching the leaf

surface to feed on.

Trichomes have basically three types of effects on insect behavior

over the leaf surface:

(1) simple impedance

(2) physical trapping by hooked hairs

(3) stickiness caused by exudates from the glandular

trichomes.

Smith et al (1975) showed that the rate of travel by the

first-instar larvae of the pink bollworm Pectinophora

gossypiella was more than six times faster on smooth

leaves the an on those with pubescence. Because of this

lack of movement, the larvae were deterred from the plant

substrate.

Hooked trichomes in French bean offer resistance, to

aphid, Aphis craccivora

Glandular trichomes are widely distributed in vascular plants that exude

gummy, sticky, or polymerizing chemical mixtures that severely impede the

insect's ability to move, feed, and/or survive.

A number of plants of the Solanum lycopersicon, Nicotiana and Medicago

spp, are particularly adept in producing sticky leaf exudates.

In certain wild potato species (Solanum polyadtnium,, S. berthaultii, and S.

tariyense), an exudate is discharged from the four-lobed head of the glandular

hairs when aphids Myzus persicac or Macrosiphum euphorbiae mechanically

rupture the cell wall (Gibson 1971)

Polyphenoloxidase and peroxidase activities are exhibited by the glandular

trichomes of S. berthaultii for oxidation of the phenolic compounds in

glandular exudates (Ryan et al 1982).

GLANDULAR TRICHOMES

LEAF SURFACE WAXES

Plant epicuticular waxes affect the feeding behavior of insects

particularly the settling of probing insects, acting as

phagostimulants or feeding deterrents. They also effect

colonisation and oviposition.

Ex: Wax bloom on leaves of crucifers deter feeding by

diamond back moth.

In onion glossy foliage provide more resistance to thrips.

THICKNESS OF CELL WELL

Cell walls thickening affect the feeding behavior of insects.

Examples:

Rice varieties containing thicker hypodermal layers offer

resistance to stem borer.

Stem density of pith and node tissues in wheat resists

damage by the wheat stem fly

Sorgham varieties resistant to shootfly due to the thickness

of the cell walls

NUTRIENT DEFICIENCY

The deficiency to the level of solids and nitrogenous

compounds in Canby an aphid resistant raspberry showed

delayed development, significantly reduced size, lower

fecundity, and extensive mortality in the aphids Amphorophora

agathonica (Hottes)

BIOCHEMICAL FACTORS

Several chemical constituents of plants that serve as

olfactory and gustatory stimuli, these may be

nutrients, sugars, amino acids, phospholipids, etc, or

non-nutritive constituents, i. e., glycosides, alkaloids,

terpenoids, etc. Such stimuli are specific and are

crucial in evoking the behavioral response of insects

(preference/antixenosis) to plants.

REPELLENTS

Plant defense compounds that prevent or reduce contact

between the insect and the substrate are known as

repellents.

Steam distillate of resistance rice varieties and nonhost

barnyard grass were found to repel Nilaparvata lugens.

The exudates from the glandular trichomes of Solanum

spp contain volatile substances Including

sesquiterpenes. These volatiles repel the aphid Myzus

persicae

ANTIBIOSIS

Adverse effect of the host plant on the biology (survival,

development and reproduction) of the insects and their

progeny due to the biochemical and biophysical factors

present in it.

Manifested by larval death, abnormal larval growth, etc.

Antibiosis may be due to

- Presence of toxic substances

- Absence of sufficient amount of essential nutrients

- Nutrient imbalance/improper utilization of nutrients

SYMPTOMS OF INSECTS AFFECTED BY ANTIBIOSIS INCLUDE

Death of young immatures

Reduced growth rate

Increased mortality in pupal stage

Small adults with reduced fecundity

Shortened adult life span

Morphological malformations

Restlessness and other abnormal behaviour

PRESENCE OF TOXINS:

Presence of toxic metabolites such as alkaloids and

glueosides play an important role in resistance to insects.

1. DIMBOA (Dihydroxy methyl benzoxazin)- Against European

corn borer, Ostrinia nubilalis

2. Gossypol (Polyphenol) -Helicoverpa armigera (American

bollworm)

3. Sinigrin - Aphids-Myzus persicae

4. Cucurbitacin -Cucurbit fruit flies

5. Salicylic acid -Rice stem borer

PRESENCE OF GROWTH INHIBITORS

Steriodal glycosides in potato and saponins in alfalfa

offer resistance to insects

Gossypol, the yellow polyphenolic pigment found in

the pigment glands of the genus Gossypium, is insect-

growth inhibitor that has resistant to the bollworm,

tobacco budworm, pink boll worm, and other tissue

borers.

NUTRITIONAL IMBALANCE

Reduction in the sugar content of the plant at the critical stages of

insect growth may adversely affect the insect.

Ex: larvae of the European, corn borer require glucose up to the

fourth instar and are capable of differentiating between varying

sugar concentrations to the, host plant tissues. Sugar deficiency

until this stage of larval development may cause antibiosis

Pea cultivars with low amino acids levels an increased sugar

content show resistance to pea aphid, Acyrthosiphon pisum

rice cultivars deficient in asparagines causes

reduced fecundity in brown plant hopper

STRUCTURAL FACTORS

Structural factors can serve as defense mechanisms for plants

when herbivores come in contact with them. The most

common contact factors that impart antibiosis resistance are

Plant-tissue toughness

Cell-wall composition

Proliferation of wounded tissues

PLANT-TISSUE TOUGHNESS

Toughness may reduce the suitability of leaves as a food source

for herbivores in several ways:

Indigestible polymers such as cellulose and lignin in secondary

tissues may reduce the rate of leaf consumption by herbivores.

Indigestible materials in tough leaves may be less suitable for

herbivore growth, development, and/or survival.

Nutrients such as proteins and carbohydrates may be less

available in tough leaves because of the hydrogen bonding

between these compounds.

Ex: Tough leaves of Salix babylonica and S. alba that can resist

tearing, erode the cutting surface of the incisors of the leaf beetle

Plagiodera versicolora

CELL-WALL COMPOSITION

The presence of neutral detergent fiber (NDF), lignin, and biogenic

silica in cell walls of plants can affect insect feeding at both

nutritional and physical level. Plants high cell wall structural

components are not desirable for herbivores (Scnber and Sansky

1981 ).

Elevated levels of indigestible fiber and silica may Increase the bulk

density of the diet to the extent that insect are

unable to ingest sufficient quantities of nutrients and water.

Ex: Silica in the rice leaves affect the feeding of stem

borer

PROLIFERATION OF WOUNDED TISSUES

Involve the proliferation of cells triggered by injury

or increased secretion 0f plant substances known to

cause the death of eggs or young larvae inside of

damaged plant

Ex: larvae of young pink bollworms were crushed or

downed by proliferating cells of the injured tissues

in certain corn line.

In mustard – necrotized zone around the base of

the egg of cabbage worm causing them desiccate.

TOLERANCE

Tolerance refers to the ability of the host plant to with

stand an insect population sufficient to damage severely

the susceptible plants.

Tolerance is a plant response to an insect pest. Whereas,

antibiosis and antixenosis resistance cause an insect

response when the insect attempts to use the resistant

plant for food, oviposition, or shelter.

This form of resistance include general vigour,

compensatory growth in individual plants and or the plant

population, wound healing, mechanical support in tissues

and organs and changes in photosynthate partitioning.

ADVANTAGES AND LIMITATIONS OF TOLERANCEAdvantages

Tolerant varieties have higher ETL

They prevent development of biotypes

They increase yield stability

Limitations

Insect populations are allowed to sustain epidemics in an

area, causing problems in other crops

It is more strongly affected by environmental extremes

than other forms of resistance

CONCLUSION The mechanism of resistance has three main

components that check the pest population from orientation, feeding and oviposition. These components are responsible for the development of resistance against various insect pest.

These resistance does not end with a generation of the insect pest, but lasts against successive generations.

These are eco-friendly and does not cause any pollution in component of the environment nor does it have any deleterious effect on man or wild life.