Dynamics of airborne conidia of the gypsy moth (Lepidoptera: Lymantriidae) fungal pathogen Entomophaga maimaiga (Zygomycetes: Entomophthorales)

Airborne conidia of Entomophaga maimaiga, a fungal pathogen of gypsy moth (Lymantria dispar), were sampled during 1992 and 1993 within forest canopies hosting gypsy moth populations. Conidia were occasionally abundant in the air in a site beginning the 1992 season with >20,000 egg masses/ha, but were almost undetectable when the resident gypsy moth population had declined to <100 egg masses/ha at the beginning of the 1993 field season. From third instar to pupation, presence of conidia in the air was episodic and infection in the resident gypsy moth population increased only after the first peak of abundance in airborne conidia. Conidial flux was positively associated with leaf wetness at lags of 5-14 and 16 h. Infection among larvae caged at 0.5 m above the ground was associated with leaf wetness, suggesting that moisture is critical for conidial survival and infection. Larvae caged on the ground (therefore, exposed to both resting spores and conidia of E. maimaiga) became infected throughout the field season, while, in comparison, larvae caged at 0.5 m (exposed only to airborne conidia) were infected sporadically during 1992 and virtually never during 1993. During 1992, infections of ground-caged larvae were initiated by both resting spores and conidia.