When young leaves are damaged, they may curl and distort. For example, this is what the Russian wheat aphid does to wheat and barley, costing growers tens of millions of dollars annually in crop losses and extra-control costs. Insects may produce galls on plants . Unusual growths on plants are caused by many insects, certain mites and some plant disease organisms. These abnormal growths are known as galls and result from the way the insect feeds on the plant.
Insects destroy fruit and seeds.
Some insects beat us to the harvest, feeding directly on the fruit or seeds we are trying to harvest. A worm in an apple probably is the larva of the codling moth. The ear of sweet corn often is already inhabited by corn earworms. Insects transmit plant diseases. Often, the insect itself causes little damage when it pauses to feed on a plant.