1. STUDIES ON NATURE OF DAMAGE AND
SYMPTOMS PRODUCED BY PESTS
Experiment No. 1

2. Nature of damage: How pest cause damage?
It varies from pest to pest, according to their feeding habits
and mouthparts.
Ex: Biting and chewing, piercing and sucking, lacerating,
mouth hook
Symptoms:
Reaction/ response of host plant to the injury caused by pest

3. Two categories
1. Direct damage : Pests feed or cause direct damage on host plants
/horticulture crops.
2. Indirect damage: Sooty moluld, nest construction, contamination
with their fecal matter, vector of phytopathogens

4. Types of direct damage
I. Damage by chewing and biting insects
A) Injury by external feeders
1. Damage to growing point:
Pest attacks growing points resulting in disruption of vertical
growth E.g.: Grape flea beetle, Mango shoot borer

5. Types of direct damage
I. Damage by chewing and biting insects
A) Injury by external feeders
2. Defoliation:
pest feed on the leaves leads to loss of foliage/ leaf area
Defoliations occur in different ways
1. Marginal feeding: Notching the edge of leaves.
E.g.: Ash or grey weevils, slug caterpillar.
1. Making holes on the leaves:
Flea beetle – pin holes
Semi-loopers – big holes
Grasshoppers – Irregular holes

6. 3. Free feeding: Feeding on the leaves by leaving only
large veins. E.g.: Lepidopteran pest.
4. Scrapping of chlorophyll: Pests scrap the green
matter and leaves appear papery/ burnt E.g.: Tobacco
caterpillar, coconut black headed caterpillar, sapota
leaf webber
5. Rolling of leaves: Two edges of leaves weaving
together with silken thread and feed inside. E.g.:
Banana leaf roller. Coconut skipper,
6. Skeletonizers: Early instar larvae scrape green matter
between veins and leaving only the veins as a
skeleton of the leaf. E.g.: Many lepidopteran larvae,
flea beetles
7. Leaf cutters: Mango leaf cutting and twisting weevil

7. 3. Bark feeding: Some larvae have habit of making holes by
constructing the webbings and feed on the bark of the trees by
remaining inside. E.g.: Bark eating caterpillar
4. Cut worms: The larvae living in the soil and cut the stem of young
plant at ground level. Eg. Cutworm, Agrotis ipsilon

8. Types of direct damage
I. Damage by chewing and biting insects
A) Injury by Internal feeders: Some pests either adults or
young ones make their way into plant tissue and go on
feed inside resulting in tunneling effect
1. Stem or shoot borers: Hard stem or shoot is penetrated by larvae
and feed downwards/upwards causing yellowing and drying of
trees. E.g.: Mango stem borer / shoot borer.
2. Flower / flower bud / fruit borer: The reproductive parts of many
plants are damaged by insect and causing the dropping of flowers
and fruits. E.g.: Pomegranate fruit borer.

9. 3. Leaf miners: The minute larvae are habituated to enter into the
two epidermal layers of leaves and scrape the green matter thereby
causing mines on leaves.
E.g.: Serpentine leaf miner, Cashew leaf miner, Mango Leaf miners
(blotch miner, linear miner)
3. Gall formers: Some insects injure the plant tissues and secrete
some compounds. These compounds enhance the meristamatic
activity and resulting gall information on leaves, twigs.
E.g.: Psyllids, thrips, cicidiomyiid maggots.

10. Types of direct damage
II. Damage by Sucking pests
Insects’ mouthparts modified for sucking the sap from various
parts of the plants. Sucking insects produce many symptoms.
Chlorosis : Yellowing of leaves - withering and drying of leaves.
E.g.: Aphids.
Faint yellow speckling : Yellow spots on the leaves. E.g.:
Whiteflies, mealybugs, scale.
Silvery/ whitening of plant tissues/ scab/brittle : Silvery lines on
the infested part. E.g.: Thrips.

11. Necrotic brown lesions: E.g.: Leaf hoppers or jassids.
Crinkling and curling: Curling of leaves either downward (mites,
aphids) or upwards (thrips, leafhoppers).
Proliferation of tissue/ eruption/scab/kajji : Due to injection of
toxins by sucking insects, there will be cell proliferation.
E.g.: Guava kajji bug.
White triangular spot – brown spot – cracks – gummosis: Coconut
eriophyid mite

12. INDIRECT DAMAGE
1. Transmitting the disease causing organisms. E.g.:
Aphids, whitefly.
2. Making harvest difficult: Red ant nests, leaf webber
3. Honey dew/ Sooty mould: Effects photosynthesis
Aphids, whiteflies, mealybug, scale, leafhoppers
4. Loss of quality of produce: E.g.:Fruit borer, fruit flies,
TMB, Thrips, stored grain pests
5. Egg laying injury: E.g. Cicada, jassid, tree hopper, cow
bug.
6. Using plant parts for making nests E.g. Red ant,
leafcutter bee.
7. Phoresy: Black ant carries nymphs of cow bug aphids ,
mealy bugs.

13. INJURY BY THE SUBTERRANEAN INSECTS
Some insects inhabiting soil and feed on roots causing
yellowing , withering, wilting and death of plants.
E.g.: Root grubs, termites, mole crickets,
Injury by the storage pests: The stored grains and
products are attacked by pests in three ways:
1. Continuations from field infestation
2. Eggs are laid in field and damage results in storage
3. Infestations in the storage. E.g.: Drug store beetle, flour
beetles,

14. Activity:
Visit the field and observe for damage
symptoms caused by different types of insect
pests.
Study question:
Collect damaged specimens of different fruit,
plantations, medicinal & aromatic crops and
prepare herbarium sheets.

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