, Volume 177, Issue 3, pp 785–797 | Cite as

Replacement of a dominant viral pathogen by a fungal pathogen does not alter the collapse of a regional forest insect outbreak

  • Ann E. HajekEmail author
  • Patrick C. Tobin
  • Kyle J. Haynes
Community ecology - Original research


Natural enemies and environmental factors likely both influence the population cycles of many forest-defoliating insect species. Previous work suggests precipitation influences the spatiotemporal patterns of gypsy moth outbreaks in North America, and it has been hypothesized that precipitation could act indirectly through effects on pathogens. We investigated the potential role of climatic and environmental factors in driving pathogen epizootics and parasitism at 57 sites over an area of ≈72,300 km2 in four US mid-Atlantic states during the final year (2009) of a gypsy moth outbreak. Prior work has largely reported that the Lymantria dispar nucleopolyhedrovirus (LdNPV) was the principal mortality agent responsible for regional collapses of gypsy moth outbreaks. However, in the gypsy moth outbreak-prone US mid-Atlantic region, the fungal pathogen Entomophaga maimaiga has replaced the virus as the dominant source of mortality in dense host populations. The severity of the gypsy moth population crash, measured as the decline in egg mass densities from 2009 to 2010, tended to increase with the prevalence of E. maimaiga and larval parasitoids, but not LdNPV. A significantly negative spatial association was detected between rates of fungal mortality and parasitism, potentially indicating displacement of parasitoids by E. maimaiga. Fungal, viral, and parasitoid mortality agents differed in their associations with local abiotic and biotic conditions, but precipitation significantly influenced both fungal and viral prevalence. This study provides the first spatially robust evidence of the dominance of E. maimaiga during the collapse of a gypsy moth outbreak and highlights the important role played by microclimatic conditions.


Epizootiology Environmental drivers Insect outbreaks Spatial lag model Dependence 



We thank R. Rabaglia and R. Reardon (USDA Forest Service) for helping to conceive, assist, and design this study. This study was only possible due to extensive assistance from R. Tatman (MD Department of Agriculture), T. Marasco (PA Bureau of Forestry), C. Asaro (VA Department of Forestry), and R. Turcotte (USDA Forest Service, Morgantown, WV) and their teams. At Cornell, samples were diagnosed and data were collated by R. Plymale, S. Long, K. Ciccaglione, C. Fritzen, M. Garvey, M. Grambor, T. James, A. Navarro, and J. Tyvoll, and J. Nix counted resting spore densities in soil samples. We thank L. Blackburn (USDA Forest Service) and J. Walter (University of Virginia) for technical assistance, and A. Liebhold and two anonymous reviewers for comments on the manuscript. This study was funded by USDA Forest Service, Forest Health Protection USDA Forest Service grant #07-CA-11420004-152.

Supplementary material

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Copyright information

© Springer-Verlag Berlin Heidelberg 2014

Authors and Affiliations

  • Ann E. Hajek
    • 1
    Email author
  • Patrick C. Tobin
    • 2
    • 4
  • Kyle J. Haynes
    • 3
  1. 1.Department of EntomologyCornell UniversityIthacaUSA
  2. 2.Northern Research StationUSDA Forest ServiceMorgantownUSA
  3. 3.Department of Environmental Sciences, Blandy Experimental FarmUniversity of VirginiaBoyceUSA
  4. 4.School of Environmental and Forest SciencesUniversity of WashingtonSeattleUSA

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