Viruses lay on a leaf until another insect of same species comes along and eats that leaf. Many viruses are easily destroyed by UV light, which has been a hindrance in developing them for commercial use. Nematodes, roundworms frequent in grasshoppers and also some other insects. Tend to get very large relative to size of insect and often sterilize the insect by destroying insides of abdomen. Parasitism Broadly interpreted this includes both predation and parasitism.
Insects have a wide variety of enemies.
These are responsible along with other environmental factors for controlling insect populations. Biological control makes use of these parasites and predators, or in some cases diseases, to regulate insects in an economical fashion. Most insect populations are under natural regulation and often man disrupts the balance by adding toxins or disrupting the environment in a way that favors herbivorous insects or, alternatively, is unfavorable to predators and parasites. Either way outbreaks may occurr. Often in island situations, new problems are introduced by man by the movement of herbivorous species without the appropriate natural enemies.