Insects are associated with a broad diversity of microorganisms in a variety of symbiotic relationships including: commensalism, mutualism, and parasitism. Internal mutualistic organisms are critical to the survival of the host, such as symbionts, which are found in mycetocytes and mycetomes of many invertebrate species. Although mutualistic organisms such as the protists associated with termites may be abundant in their insect hosts, they are not by definition pathogenic to the host insect. Entomopathogens, on the other hand, result in a variety of conditions in host insects that are subtly to distinctly unfavorable to the host. Disease in insects results from the direct effects of infection and/or from toxemia. An astronomical number of entomopathogens cause disease.
