FUNGAL AND VIRAL EPIZOOTICS IN GYPSY-MOTH (LEPIDOPTERA, LYMANTRIIDAE)POPULATIONS IN CENTRAL NEW-YORK

The activity of the gypsy moth fungal pathogen Entomophaga maimaiga wa s documented from 1991 to 1996 in central New York. This fungus had be en introduced to the area in 1990 but also generally spread throughout the region in 1990-1992. In 1991, gypsy moth populations were abundan t in 8 mixed hardwood plots (mean +/- SE = 15,295 +/- 4373 egg masses/ ha), the gypsy moth nuclear polyhedrosis virus (LdNPV) was the most im portant cause of larval mortality by microorganisms, and by the end of the season, populations had decreased to 6875 +/- 1345 egg masses/ha. During 1991, E. maimaiga-infected larvae were found at 7 of 8 plots c ausing 0-37% infection but this was not associated with 1990 E. maimai ga infection levels. In 1992, the major cause of larval mortality by m icroorganisms was E. maimaiga, with infection levels ranging from 64 t o 98%; LdNPV was also present at all 11 plots sampled. At lower densit y plots in 1992, E. maimaiga infections only increased dramatically du ring 5th and later instars. In higher density plots, 16 and 24% of 2nd and 3rd instars per the two early June sample dates were infected by E. maimaiga but infection levels once again peaked during later instar s, although earlier in higher than lower density sites. During 1992, m ore cadavers of 4th and 5th(+) instars produced resting spores in the higher density plots than in the lower density plots, suggesting incre ased secondary transmission by conidia actively ejected from cadavers. The amount of rain falling during the periods of time that larvae wer e active differed by year; LdNPV was the dominant pathogen during the dry 1991 spring, while E. maimaiga flourished during 1992, when rain f ell at approximately normal levels. From 1993 to 1996, gypsy moth popu lations remained low, with almost no LdNPV infections recovered, and E . maimaiga infections increased only after larval densities increased. (C) 1997 Academic Press.