TYPES OF SPORES PRODUCED BY ENTOMOPHAGA-MAIMAIGA INFECTING THE GYPSY-MOTH LYMANTRIA-DISPAR

We investigated the association of environmental factors (temperature, photoperiod, host molting status) and fungal factors (isolate, dose, strain attenuation) with the production of conidia versus resting spor es by the entomopathogenic fungus Entomophaga maimaiga infecting the l arvae of the gypsy moth Lymantria dispar. Fungal spores produced from individual cadavers of larvae killed by E. maimaiga can include conidi a discharged from the cadaver surface, resting spores (azygospores) wi thin the cadaver, or both spore types. The single factor having the gr eatest impact on the type of spore produced was host age; second insta rs virtually never contained resting spores, independent of temperatur e, while fifth instar cadavers contained resting spores more frequentl y at higher temperatures. However, there was increased conidiation at lower temperatures. Photoperiod was the only factor studied that did n ot significantly influence the type of spore produced. Resting spore p roduction was negatively associated with the molting cycle; cadavers o f those larvae that molted or exhibited premolt characteristics during the period between infection and death contained fewer resting spores . Increased fungal dose yielded more resting spores, as did extensive serial passage, which simultaneously caused a decrease in conidiation. Fungal isolates varied in the types of spores produced, with fewer ca davers of larvae killed by the least virulent isolate discharging coni dia. Results from this study support the hypothesis that both the cond ition of the fungal pathogen as well as the environment surrounding it contribute to the types of spores produced.