How Pests Feed?

1 Sapsuckers Pests such as aphids, whitefly, and red spider mite use needlelike mouth-parts to pierce plant stems and suck sap, resulting in reduced vigor and growth distortions (as in aphid damage). Bacterial infections can also enter the plant via the wounds. Sapsuckers can transmit viruses, and their waste (honeydew) provides a food source on which molds thrive.
2 Root-feeders Many insect larvae, including some moth caterpillars, beetle grubs such as wireworms, vine weevil, cabbage root fly, and parasitic nematodes known as eelworms, graze on roots. damage restricts nutrient and water uptake, restricting growth and causing wilting; root crops may be rendered inedible.
3 Leaf-feeders Many caterpillars (sawfly), adult beetles and their grubs, and of course slugs and snails, graze on leaves and sometimes stems. other larvae mine or tunnel leaves. Leaf damage reduces the area where photosynthesis operates, sapping the plant’s strength and reducing fruit set.
4 Flower-feeders Earwigs, psylla, thrips, and Japanese beetles feed on flower heads and buds. damage may be significant, but is often only cosmetic. Many bird species strip fruit trees and bushes of flower buds in late winter and early spring, when food is scarce.
5 Gall-formers The presence of some fly and wasp larvae, as well as mites, causes distortions of growth known as galls; this is an “oak apple” caused by a tiny wasp. Galls are usually harmless, but some gall-formers transmit viruses.
6 Fruit-feeders Some caterpillars, beetle grubs, and fly larvae feed on developing fruits; birds and  wasps feed on ripening fruit. damage is usually limited, but the soiled fruit can be unpalatable, and other infections may enter the wounds.