INTRODUCTION AND ESTABLISHMENT OF ENTOMOPHAGA-MAIMAIGA, A FUNGAL PATHOGEN OF GYPSY-MOTH (LEPIDOPTERA, LYMANTRIIDAE) IN MICHIGAN

In 1991, late instars of gypsy moth, Lymantria dispar (L.), were sampl ed and diagnosed for infections of the pathogenic fungus Entomophaga m aimaiga Humber, Shimazu & Soper and for gypsy moth nuclear polyhedrosi s virus (NPV) at 50 sites in Michigan. Approximately 1,500 larvae were collected and reared from these sites, and no infections of E. maimai ga were detected. From 1991 to 1993, we tested the efficacy of 2 inocu lative-release methods for E. maimaiga in replicated plots at 3 resear ch sites by relocating soil containing E. maimaiga resting spores from Massachusetts to Michigan or by releasing inoculated larvae onto bole s of trees. In the 2nd yr after introduction, E. maimaiga became estab lished (9-40% infection) where both inoculation methods were used, and a low level of infection was detected in control plots (0.5-2.4%). In the 3rd yr, epizootics of E. maimaiga occurred at all 3 research site s, with the incidence of infection ranging from 20 to 99% in both trea ted and control plots. Infection levels were correlated with precipita tion and relative humidity greater than or equal to 90% for 2 wk prece ding larval sampling. In 1993, egg mass densities at the 3 E. maimaiga study sites averaged 3- to 10-fold lower than in adjacent oak forest. We found that it is easy to introduce E. maimaiga to new locations ev en in the midst of an epizootic of gypsy moth NPV and that E. maimaiga reduces gypsy moth populations to levels lower than that caused by NP V alone.