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 1/4th 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