16.1 Pathogens of insects
Insects are the most diverse group of animals on Earth, occurring in most terrestrial environments, though only a few species are found in marine habitats, as these are dominated by the crustaceans. Over a million species of insects have been described, which is more than half of known living organisms, and taking into account estimates of the number of species that are yet to be described, the class Insecta probably includes about 90% of all species on the planet. However, these considerations are affected by the fact that insects inevitably suffer many infectious diseases caused by microorganisms, and many entomologists believe that there may be more species of insect pathogens than there are species of insects.
Insect species are infected by pathogenic viruses, bacteria, and protozoa, as well as two groups of organisms that have uncertain relationships, the microsporidia and the trichomycetes; all of these tend to cause infection after being ingested by the insect.
The true fungi that infect insects are invasive pathogens; that is, they have the ability to produce enzymes and hyphae that can penetrate the insect cuticle. These disease organisms often act as natural control agents by regulating the population size of insect pests. There is consequently considerable interest in harnessing this capability commercially to control insects that are considered to be pests because of their adverse effects on our agricultural activities or because they act as vectors of human diseases.
Updated December 17, 2016