Pests Beneficial Organisms Insect-Transmitted Diseases Management Options Other Resources Contact a Specialist Parasitic Wasps and Flies (Parasitoids) Many insects are preyed upon by specialized parasites known as "parasitoids." A parasitoid lives in or on its host, leading inevitably to host death. Most pest insects in potato fields are attacked by parasitoids, especially in organic fields or conventional fields with few insecticide applications (generally, parasitoids are very sensitive to insecticides).   Cocoon of a caterpillar-killing parasitoid.   Adult of a caterpillar-killing parasitoid.