Possibility for recent origin of the gypsy moth (Lepidoptera: Lymantriidae) fungal pathogen Entomophaga maimaiga (Zygomycetes: Entomophthorales) in North America

A model based on weather records and gypsy moth and pathogen developmental times was used to investigate environments favorable for development of the fungus Entomophaga maimaiga Humber, Shimazu and Soper, a pathogen of the gypsy moth, Lymantria dispar (L.), in the northeastern United States. The fungus was first noticed in 1989, and model results were obtained using data from that year from almost 400 weather stations from Pennsylvania and New Jersey to Maine. The most favorable areas in that year were parts of Connecticut, the northern third of Pennsylvania, and the southern half of New York State. The distribution of the fungus during that year, and the known ability of the fungus to spread, is consistent with an origin for the epizootic in Connecticut. When the model was run using weather records in Connecticut from 1969 to 1995, the most favorable year for development of E. maimaiga was 1989, the year in which the pathogen was first discovered in North America. However, extensive defoliation and at least moderately favorable weather conditions suggested that the fungus would also have been observed in 1971 if it had been present then. Also, model results using weather records in Massachusetts showed that the year 1945 was very favorable for development of E. maimaiga in that state. Because there is no evidence that the fungus was present at these times, it is probable that E. maimaiga became established in North America relatively recently