Phytophagous insect and their host finding mechanism

its about how phytophagous insects find host for feeding and oviposition

1. Phytophagous insect and their host finding mechanism

2. Introduction Members of insects which consume either root, leaves, bore on stems or feed on whole plants occupy diverse species of insects ,about five lakhs of species and occupies 1/4 th of total species Monophagous or polyphagous External part of plant eaters and internal fluid feeder are included in phytophagous insects

3. There is difference in feeding behavior of different stages of insects Food choice of insects differ species to species and major contributing factor for host selection is their mouth parts Host finding mechanism and acceptance of host involves searching, landing and contact evaluation (Renwick, 1988) Many sense organs such as visual, olfactory, tactile, gustatory are used for detection of host plant Abundance of plant species also determines the insect host selection When previously feeding host plant is far, there may be chance of host shifting It is said that insects prefer those plants more where its mother had laid egg and where the insect had been hatched

4. Phytophagous order ORTHROPTERA They choose those plants which provide them right amount of sugar, amino acids and vitamins Grasshoppers mainly prefer green lawn, fallow land with grasses Locusts reject dicotyledons and feed some species of monocots only Crickets are found in fields, meadows, forests, grasslands, trees, bushes and prefer seedlings

5. DIPTERA Effect of color and odor helps in attraction of fruits flies towards fruits If visual character is strong then odor do not play primary role in attraction Cabbage root fly turns head towards wind movement and flies in the direction of wind for detection of source of odor

6. LEPIDOPTERA Caterpillar of cabbage butterfly is attracted towards the volatile produced by above ground parts of cabbage Female of butterfly locate and lay eggs on the plants which are preferred by their larva for feeding Butterflies have taste receptors on their feet to locate by tapping legs on surface Spines on the back of leg have chemo receptors that detect matching chemical

7. continue Pink bollworm feeds only on boll of cotton and feeds on leaves only in unfavorable condition Corn seedling releases large amount of terpenoids that causes attraction to spodoptera species low intensity and short wavelength of light reflected from field attract moth for oviposition and feeding day flying moths are more attracted by green color Crambidae prefer to lay eggs on vertical leaves than horizontal leaves Silkworm have receptors towards bitter substances Plutella responds nine different glucosides found in Cruciferae groups

8. COLEOPTERA Chrysomelidae feed on crucifers having high amount of glucosinolates Some species of cerambycidae used visual or olfactory cues alone or both combined for finding hosts Weevil larva prefer feeding on roots of deciduous plants while adults feed on above ground part of same plant Cucumber bettle feeds on Cucurbitaceae cucurbitacin Epilachna feeds on Phaseolus species due to cyanogenic glucoside and linamarin

9. Hemiptera Aphididae have character of hovering and accumulating in a specific place association of vectors and virus causes the specificity of host and symbiosis of virus vector causes selection of host plant in aphididae Brown winged sting bug prefers to feed on leguminous and solanaceous plants Cone feeding conifer bugs have infra-red radiation reception organ which helps in perception of irradiation

10. Continue.. Insects of pyrillidae (potato psylla) has host range of 40 species in 20 families but they have more preference on Solanaceae and Convolvulaceae In mealy bugs tabbing with labium and antennae helps to differentiate between more preferred and less preferred host plant Mealybug prefer cassava as cassava contains high amount of cyanide in leaves, root and stem Sap sucking insects prefer to feed on smaller plants than larger plants

11. Based on reaction produced by plants in response to insects, the chemicals are classified as; Attractants: Volatiles present on plants which helps insects in searching host plant for oviposition are included under attractants Repellents: Repellents are alkaloids, terpenoids, phenolics etc. these compounds are released by plants against herbivorous dipterans Feeding or oviposition stimulants: shallow tail butterfly feeding on Aristolochla species, oviposition is stimulated by chemical Aristolochic acid Citrus feeding butterfly is attracted towards methanol found on fresh leaves of citrus. Deterrent: They may cause to stop feeding

12. CONCLUSION Different stages of insects show specificity of host differently Larval stages show more specificity than adult stages plants produce complex volatiles which makes difficulty for insects to select specific volatile from plant Odor and color show high preferences in host selection primarily Secondary factor for selection of host plant is chemical constituents present in plant Tactile cues are used by aphids and other sucking and virus carrying vectors