Friction-associated conidial detachment of the entomopathogenic fungus Beauveria amorpha from the cuticle of a scarab grub, Anomala cuprea, in the soil

Entomopathogenic fungal conidia are detached from the host cuticle by several environmental factors. Larvae of the scarab grub, Anomala cuprea, inhabit the soil, and are constantly in contact with the soil. The larvae were treated with imidacloprid to suppress the mobility, and then treated with fluorescein isothiocyanate labelled conidia of the entomopathogenic fungus, Beauveria amorpha. In the case of non-paralyzed larvae without imidacloprid treatment, conidia on the vertex, dorsum and abdomen became detached by 12 h after application. In contrast, the number of conidia on paralyzed larvae with imidacloprid treatment remained stable throughout the test period. In parallel with conidial detachment from non-paralyzed larvae, the number of conidia detected in the rearing soil increased. These results indicated that the fungal conidia adhering to the surface of scarab grubs are detached by friction with soil in association with the larval movement, suggesting that insect movement may be an important factor that affects the infection with pathogens.