The Plant‐Associated Fungus Chaetomium globosum Can Directly Infect and Kill Aphids

Chaetomium globosum is widely recognized as a potential biological control agent in plant pathology, but it has not been shown to function as an entomopathogen. The direct pathogenicity of two plant‐associated strains of C. globosum towards the cotton aphid, Aphis gossypii Glover, was investigated. Varying concentrations of spore suspensions of two C. globosum strains were applied to second‐instar aphids in dipping and spray bioassays, then maintained either in Petri dishes or on whole plants. Spores of the entomopathogenic fungus Beauveria bassiana were used as a positive control. The number of surviving aphids was recorded daily for 14 days post‐inoculation to compare survival probabilities between treatments. After death, all cadavers were surface‐sterilized and plated to confirm mycosis. In the dipping bioassays, aphid survival was significantly lower across all fungal treatments and concentrations than in water. In the spray bioassays, survival was significantly lower among aphids exposed to fungi at higher spore concentrations in Petri dishes. However, fungus treatment did not affect survival when the aphids were kept on whole plants. Our results demonstrate that some C. globosum strains can directly infect and kill insects as hosts. Broadly, this suggests that some plant‐associated fungi encountered by insect herbivores may be capable of infecting and killing them. However, our results also indicate that environmental conditions strongly influence these fungi's pathogenicity to insects and that this pathogenicity is likely limited in the field.