Inoculative Releases and Natural Spread of the Fungal Pathogen Entomophaga maimaiga (Entomophthorales: Entomophthoraceae) into U.S. Populations of Gypsy Moth, Lymantria dispar (Lepidoptera: Erebidae)

While emphasis with entomopathogens has often been on inundative releases, we describe here historic widespread inoculative releases of a fungal entomopathogen. Several U.S. states and municipalities conducted inoculative releases of the gypsy moth, Lymantria dispar (L.) (Lepidoptera: Erebidae), pathogen Entomophaga maimaiga Humber, Shimazu et Soper (Entomophthorales: Entomophthoraceae) after 1993, as gypsy moth populations spread into the Midwest and North Carolina. This Japanese pathogen first caused epizootics in northeastern North America in 1989 and methods for its inoculative release were tested and proven to be effective from 1991 to 1993. After 1993, spores in soil or in late instar cadavers were collected during or after epizootics and were released inoculatively into newly established populations of this spreading invasive; the goal was that spores would overwinter and germinate the next spring to infect larvae, thus speeding pathogen spread and hastening the development of epizootics in newly established populations. The fungus was released in gypsy moth populations that were separated from areas where the fungus was already established. In particular, extensive releases by natural resource managers in Wisconsin and Michigan aided the spread of E. maimaiga throughout these states. Where it has become established, this acute pathogen has become the dominant natural enemy and has exerted considerable influence in reducing gypsy moth damage. While this pathogen most likely would have invaded these new regions eventually, releases accelerated the spread of E. maimaiga and helped to reduce impacts of initial outbreaks, while further outbreaks were reduced by the pathogen’s subsequent persistence and activity in those areas.