Foreword - CCS HAU, Hisar

insects is often seen by uneven or broken margins on the leaves, skeletonization of the
leaves, and leaf mining. Chewing insects can be beetle adults or larvae, moth larvae
(caterpillars), and many other groups of insects. The damage they cause (leaf notching, leaf
mining, leaf skeletonizing, etc.) will help in identifying the pest insect.
Injury by Chewing Insects
Perhaps the best way to gain an idea of the prevalence of this type of insect damage is
to try to find leaves of plants with no sign of insect chewing injury. Armyworms, grasshoppers,
hairy caterpillars, beetles are common examples of insects that cause chewing injury.
Chewing Damage or Rasping Damage:
Entire leaf blade consumed by various caterpillars, canker worms, and webworms. Only
tougher midvein remains.
Distinct portions of leaf missing.
Leaf surfaces damaged: “Skeletonization” of leaf surface. Slugs, beetle larvae, pearslug
(pear sawfly larvae), elm leaf beetle, and thrips.
Leaves “rolled”: Leaves that are tied together with silken threads or rolled into a tube
often harbor leafrollers or leaftiers, i.e. omnivorous leaftier.
Leaf miners feed between the upper and lower leaf surfaces. If the leaf is held up to the
light, one can see either the insect or frass in the damaged area (discolored or swollen
leaf tissue area), i.e. citrus leafminer, pea leaf miners.
Petiole and leaf stalk borers burrow into the petiole near the blade or near the base of
the leaf. Tissues are weakened and leaf falls in early summer.
Twig girdlers and pruners, i.e. vine weevil and twig girdling beetle.
Borers feed under the bark in the cambium tissue or in the solid wood or xylem tissue.
Damage is often recognized by a general decline of the plant or a specific branch. Close
examination will often reveal the presence of holes in the bark, accumulation of frass or
sawdust-like material or pitch, i.e. mango stem borer.
Root feeders, larval stages of weevils, beetles and moths cause general decline of plant,
chewed areas of roots, i.e. root weevil, white grubs.
Feed on the growing points or plants and thus retard the growth as in the case of the
grapevine flea beetle Scelodonta strigicollis.
Feed on the leaves and defoliate the plants causing reduction in assimilative leaf area
and thus hinder growth. The semilooper caterpillar on castor, the red hairy caterpillar on
groundnut, and the slug caterpillar on mango and castor are some examples.
Make small holes in the leaves by feeding. The flea beetle on radish and sunnhemp
cause this type of damage.
Feed on a layer of surface tissue of leaf (e.g. larvae of the diamond back moth on cabbage
and cauliflower) or superficially on the surface tissue (e.g. grubs and adults of the beetles
Epilachna spp. on brinjal and bittergourd).
Leaves riddled with large holes of irregular shape and size due to feeding (e.g. cabbage
semilooper Trichoplusia ni).
16