This document discusses the different types of damage insects can inflict on plants. It is divided into several sections:
1) Direct effects of feeding by chewing and sucking insects. Chewing insects cause damage like holes, notches and defoliation. Sucking insects cause chlorosis, silvering, and hopper burn.
2) Indirect effects like making harvest difficult, reducing quality, and spreading disease.
3) Injury by internal feeders like borers, worms, leaf miners and gall insects.
4) Injury to underground parts by root feeders.
5) Injury to stored products which can continue from field or storage attacks.
Various examples are given for
3. 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 effects
2. Sucking insects
4. A. Direct effects of feeding
I. 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
5. 2. Feed on the leaves and defoliate the plants causing reduction in
assimilative leaf area and thus hinder growth
Eg : 1.Semilooper caterpillar, Achaea janata on castor
6. 2. Red headed hairy caterpillar, Amsacta albistriga on Ground nut
10. 4. Make small holes in the leaves by feeding
Eg : Flea beetle causes this type of damage on radish and
Sunhemp
11. 5. Feed on a layer of surface tissue of the leaves
Eg : Larvae of the diamond
back moth, Plutella xystella
on Cabbage and Cauliflower
12. Or feed superficially on the surface tissue
Eg : Grubs and adults of epilchna beetle,
Henosepilachna vigitioctopunctata on Brinjal and Bitter gourd
13. 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
14. 7. Roll up the leaves and feed within
Paddy leaf roller – Cnaphalocrocis medinalis
Cotton leaf roller- Sylepta derogota
15. 8. The larvae feed on the bark of the plants or trees while being
concealed 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.,
16. 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
17. 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
18. 2. The larvae of spotted pod borer – Maruca vitrata web the
flower buds and flowers on red gram and feed on them
20. 11. Nibble and cut off ear heads
Eg : Rice grass hoppers
21. 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
22. 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
23. Eg : 1. Cow pea aphids – Aphis craccivora on Lab-lab, Ground nut,
and Gliricidia
24. 2. Yellow speckling of leaves may be produced due feeding
Eg : Castor whitefly – Trialeurodes ricini
28. White spots on the upper surface of the leaves caused by
Stephanitis typicus on coconut
29. 4. Hopper burn or Necrotic brown lesion : Typical injury
produced by leaf hoppers / plant hopper
Eg : 1. Brown plant hopper – Nilaparvatha lugens on rice
31. 5. Crinkling or curling of leaves is caused by insects like Aphids , Thrips
and leaf hoppers – Eg : Thrips , Scirtothrips dorsalis on Chillies
32. 6. Vitality of the plants gets reduced and premature dropping
of leaves in case of Tomato whiteflies – Bemisia tabaci
33. 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
34. 8. Premature fall of fruits as in Citrus caused by the fruit sucking moths
Eudicima phalonia
E. materna
35. III. Injury by Internal feeders
The 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
36. 1.Borers
When 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.
37. Rice stem borer : Scirpophaga incetulas –
Larva enter in to the stem and cause
death of the central shoots i.e
dead heart symptoms
38. Soghum stem borer – Chilo partellus larvae enter into the stem and
cause death of the central shoots i. e dead heart symptoms
50. 4. Gall insects
Immature 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
53. 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
56. V. Injury to Stored products
In 3 ways the stored products are attacked by insects
57. 1. It may be continuation
of a field attack
In storage
Hatching 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 condition
Larvae mine in to the petiole as a result drooping symptoms and finally produces
blotches on the leaves
Eg : Potato tuber moth
Phthorimoea operculella
58. 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
59. 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
60. 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
61. Rice moth – Corcyra cephalonica on Maize
It attacks broken grains and flours especially the milled products,
which are heavily damaged if neglected
63. 1. Making the harvest more difficult
Heavy incidence of some pests on crops makes the harvest
of the crop more difficult
Eg : 1. Cabbage infested heavily with aphids
65. 2. Kapas from cotton bolls damaged by pink boll worm
66. 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
75. 2. BPH – Nilaparvatha lugens – A vector of grassy stunt virus
76. 3. Bunchy top of banana – Transmit by aphid , Pentalonia nigronervosa
77. 4. Sterility mosaic virus of red gram transmit by Eriophyid mite,
Aceria cajani
78. c. Injury by other methods
1. Injury by egg laying
Insects 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
79. 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
80. 2. Use of plant parts for making nests
Some 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.
84. 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;
85. Ants carry the aphids from one plant to the other plants
86. Red ants carry the mealy bugs from one plant to other plants
