Entomogenous nematodes and their associated bacteria are considered nontoxic to plants and mammals. Steinernema feltiae, used against larvae of a wide variety of soil-dwelling and boring insects, is the main nematode species available at retail in the United States. Because of moisture requirements, it is effective primarily against insects in moist soils or inside plant tissues. Prolonged storage or exposure to extreme temperatures before use may kill or injure the nematodes. Most effective in cool temperatures, they will persist for only two to four weeks following application.
Fungi are another kind of pathogen sometimes used for insect control.
Most fungi are spread by asexual spores called conidia. To germinate, the conidia usually require free water or very high humidity. But unlike bacteria, fungi do not have to be eaten by a pest to be effective. They can germinate on the insect's cuticle and develop special structures that penetrate into the insect's body. Few fungi pathogens are commercially available in the United States.