Entomophaga grylli

Appearance

The fungus is a species complex with several different pathotypes, each one of which seems to be host-specific to different subfamilies of grasshoppers. The pathogen is being investigated for its possible use in biological pest control of grasshoppers.

Behavior

"Entomophaga calopteni" only produces resting spores, which are available to infect grasshoppers the following year. "E. macleodii" and "E. praxibuli" produce both resting spores and asexual conidia. Large numbers of conidia are produced under wet, humid conditions, and several cycles of infection can then occur in a single season. After landing on a potential host, a conidium produces a germ tube which can grow through the cuticle into the hemocoel; once there, it produces amoeboid protoplasts. These are cells without cell walls and seem to elude the insect's immune system. They multiply and kill the host. In some members of the species complex, they develop hyphae with cell walls and grow through the cuticle, producing conidiophores and infective conidia. In these and other members of the species complex, they also have an intermediate stage producing resting spores with cell walls.

After the insect cadaver has fallen to the ground, the resting spores overwinter in the soil. A portion of them germinate in the spring, producing other spores that are forcibly ejected from the soil, landing on low vegetation where they come into contact with grasshoppers. They penetrate through the cuticle, proliferate and develop rapidly, the infected insect dying within about one week. At an advanced stage of the disease, an infected individual climbs to the top of a plant and dies with its limbs gripping the stem and its head pointing upwards. Some resting spores remain dormant in the soil for two or more years. Epizootic outbreaks of disease in grasshopper populations in North America have been attributed to "E. grylli" but are usually localised and sporadic rather than widespread. They have been credited with ending many outbreaks of grasshopper species over the decades.