In nature, there are a number of organisms that may attack insects. In some cases, these act as controls for insect pests. But often these organisms do not distinguish between beneficial insects and insect pests.
According to UK Extension Entomologist, Lee Townsend, the rainy season has been ideal for development of many types of fungus that attack insects. This summer, a client brought in this sample of green bottle flies (see the photo above). They were a curiosity because there were hundreds of them dead and ‘plastered’ to leaves of a backyard tree. These were killed by a fungus that is specific to these flies.
The caterpillar in the photograph below was killed by a fungus that acts in the same way. Dr. Townsend said the white covering seen on this now-dead caterpillar contains fungal spores that will spread to keep the fungus alive. Infected caterpillars typically climb to or near the tops of plants before they die. The spores are then released at a height where they can fall back on or blow to nearby plants where other caterpillars will eat them and become infected.