Laboratory Bioassays Testing the Host Range of the Gypsy Moth Fungal Pathogen Entomophaga maimaiga

The fungal pathogen Entomophaga maimaiga causes epizootics in gypsy moth, Lymantria dispar, populations, but little is known about the effects of this pathogen on other insect species. The host specificity of E. maimaiga was evaluated by externally inoculating larvae with conidia in the laboratory. Larvae were considered successfully infected if E. maimaiga produced spores in/on cadavers. A total of 78 species of Lepidoptera (aside from L. dispar) from 10 superfamilies, predominantly natives to the Appalachian forests, were challenged during bioassays. Cadavers of 35.6% of the species produced spores after conidial inoculation; infection occurred in 7 of the 10 lepidopteran superfamilies tested, although infection levels were <50% for all superfamilies except Bombycoidea, Sphingoidea, and Noctuoidea. Within both the Bombycoidea and Sphingoidea, only one species became infected at >50%. In the Noctuoidea, the Lymantriidae was the only family with high levels of infection. Thirty-six of the species exposed to conidia were also injected with protoplasts of E. maimaiga to determine the contribution of conidial penetration to species susceptibility. For 23.5% of the species challenged using both methods, E. maimaiga could not successfully develop regardless of infection methodology. In 17.6% of the species, E. maimaiga did not infect after conidial inoculation but caused high levels of infection after protoplast injection. An overall analysis found decreased infection as a result of conidial penetration among larvae with little surface sculpturing and with only primary or short secondary setae. Conidia produced from cadavers of Danaus plexippus larvae injected with protoplasts were infective to L. dispar, suggesting that conidia produced in alternate hosts are infective. Finally, seasonality of activity of E. maimaiga showed that E. maimaiga spores in soil began causing infections approximately 2 weeks before L. dispar eggs began hatching and continued infecting L. dispar larvae in the field through pupation.