Release, establishment, and initial spread of the fungal pathogen Entomophaga maimaiga in island populations of Lymantria dispar

Biological invasions represent a major threat to the function and composition of ecosystems. Although the degree of invasion success of a non-native species and the consequent damage it causes can vary among and within invading species, the absence or presence of natural enemies associated with the invader can also play roles in the invasion dynamics. We used newly established, spatially isolated populations of the gypsy moth, Lymantria dispar (L.), on some of the islands within the archipelago of the Apostle Islands National Lakeshore in northwestern Wisconsin, USA, to study the establishment and initial spread of two releases of the entomophthoralean fungus Entomophaga maimaiga. We also explored patterns in rates of infection by the L. dispar nucleopolyhedrovirus, which was also released on three islands, and in the rates of parasitism by generalist parasitoids. The mean initial rate of spread by E. maimaiga following its successful establishment was 0.8 km year−1, although it was detected as far as 6.1 km from a release site after one year. Infection rates by both entomopathogens were highest on those islands where they were released; however, rates of parasitism by larval parasitoids were highest where neither pathogen had been released, suggesting that pathogens outcompete larval parasitoids. Understanding the intricate relationship between an invading host species and their associated pathogens during the early stages of invasion could enhance the use of biological control in invasive species management.

Map: Recoveries of Entomophaga maimaiga in 2008 (red stars) and 2009 (blue stars) on the Apostle Islands National Lakeshore, Wisconsin, USA (Map Credit: Laura Blackburn).Top photo: Lymantria dispar larvae on Stockton Island, Wisconsin, USA, 2007 (Photo Credit: Patrick Tobin).Bottom photo: L. dispar larva killed by E. maimaiga at Rocky Arbor State Park, Wisconsin, USA, 2007 (Photo Credit: Patrick Tobin).Figure optionsDownload as PowerPoint slideHighlights
► Entomophaga maigaiga established and spread at a mean rate of 0.8 km year−1.
► Pathogen prevalence was highest on islands where pathogens had been released.
► Levels of larval parasitoids were significantly lower where pathogens were released.
► Understanding pathogen spatial and temporal dynamics optimizes their release.