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 wer
e almost undetectable when the resident gypsy moth population had declined
to <100 egg masses/ha at the beginning of the 1993 held season. From third
instar to pupation, presence of conidia in the air was episodic and infecti
on in the resident gypsy moth population increased only after the first pea
k 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 a
t 0.5 m above the ground was associated with leaf wetness, suggesting that
moisture is critical for conidial survival and infection. Larvae caged on t
he ground (therefore, exposed to both resting spores and conidia of E. maim
aiga) became infected throughout the field season, while, in comparison, la
rvae caged at 0.5 m (exposed only to airborne conidia) were infected sporad
ically during 1992 and virtually never during 1993. During 1992, infections
of ground-caged larvae were initiated by both resting spores and conidia.
(C) 1999 Academic Press.