Gypsy Moth

Fungal Disease

Research Issue

Tree trunk covered in gypsy moth caterpillars killed by Enteromaphaga maimaga. Photo by Mark Ashton, Yale University.  Used with permission.One of the great mysteries of gypsy moth (GM) in eastern North America is the origin of the fungus Entomophaga maimaiga, now the dominant natural enemy of GM. This fungus is in the order Entomophthorales, which are mostly insect pathogens, and “maimaiga” is the Japanese word for “gypsy moth.”  In Japan, where E. maimaiga is a native pathogen of GM caterpillars, the fungus is known to cause periodic “epizootics” or “epidemics” that often result in widespread collapse of GM populations. However, when E. maimaiga was introduced for the biological control of GM near Boston, MA in 1910-1911, workers concluded that the introduction was a failure because they were unable to find infected caterpillars.

It was not until 1989 that E. maimaiga was discovered as the primary cause of an extensive GM epizootic in New England and several adjacent states. Since then numerous epizootics have been observed as the fungus spread across eastern North America, and scientists are working to determine how E. maimaiga will affect the long-term dynamics of the gypsy moth.

Numerous constraints limit the use of entomopathogenic fungi for use as myco-insecticides (pest control). Most of these problems relate to the production and application of material. The fungus spreads through aerial dispersion of actively ejected asexual spores from cadavers of gypsy moth larvae it has killed. The fungus persists in the top layer of soil as resting spores; these have been shown to persist for at least 11 or 12 years, probably longer.

The fungal pathogen Entomophaga maimaiga has become prevalent in gypsy moth populations throughout North America. How the fungus spreads and what affects its ability to infect GM populations is still not entirely understood. One of the factors is weather—temperatures and moisture levels. The extent to which E. maimaiga suppresses GM populations below outbreak levels is characteristically variable both among sites and among years and therefore difficult to predict. As such, there remains a need to clarify the linkages among weather, E. maimaiga, and gypsy moth dynamics.

Our Research

In this study, NRS entomologists measured fungal infection rates over 3 years concurrently with meteorological variables at a number of sites in central Pennsylvania, associating meteorological conditions with E. maimaiga infection rates to better understand GM—fungus dynamics. Fungal mortality was assessed using both field-collected larvae and laboratory-reared larvae caged on the forest floor. This research has been funded by US Forest Service State & Private Forestry and AFFRI.

Expected Outcomes

These gypsy moth—weather relationships may be helpful in understanding how GM dynamics vary across space and time, and in forecasting how the GM and fungus will interact as they move into warmer or drier areas, or new weather conditions occur due to climate change.

Research Results

There were significant positive effects of moisture-related variables (rainfall, soil moisture, and relative humidity) on GM mortality due to fungal infection in both data sets, and significant negative effects of temperature on the mortality of field-collected larvae. Lack of a clear temperature relationship with the mortality of caged larvae may be attributable to differential initiation of infection by resting spores and conidia or to microclimate effects.

Bittner, Tonya D.; Hajek, Ann E.; Liebhold, Andrew M.; Thistle, Harold; Cullen, Dan 2017. Modification of a pollen trap design to capture airborne conidia of Entomophaga maimaiga and detection of conidia by quantitative PCR. Applied and Environmental Microbiology. 83(17): e00724-17-. 11 p. https://doi.org/10.1128/AEM.00724-17.

​Reilly, James R.; Hajek, Ann E.; Liebhold, Andrew M.; Plymale, Ruth. 2014. Impact of Entomophaga maimaiga (Entomophthorales: Entomophthoraceae) on outbreak gypsy moth populations (Lepidoptera: Erebidae): the role of weather. Environmental Entomology. 43(3): 632-641. https://doi.org/10.1603/EN13194.

Tobin, Patrick C.; Hajek, Ann E. 2012. Release, establishment, and initial spread of the fungal pathogen Entomophaga maimaiga in island populations of Lymantria dispar. Biological Control. 63: 31-39. https://doi.org/10.1016/j.biocontrol.2012.06.004.

Hajek, Ann E.; Tobin, Patrick C. 2011. Introduced pathogens follow the invasion front of a spreading alien host. Journal of Animal Ecology. 80: 1217-1226. https://doi.org/10.1111/j.1365-2656.2011.01870.x.

Plymale, R.C.; Liebhold, A.M.; Hajek, A.E.  2009. Spatial population dynamics and heterogeneity of an insect/pathogen interaction. In: McManus, K.A; Gottschalk, K.W., eds. Proceedings, 20th USDA Interagency Research Forum on Invasive Species, 2009; 2009 January 13-16; Annapolis, MD. GTR-NRS-P-51. Newtown Square, PA: USDA Forest Service, Northern Research Station: 92.

Hajek, Ann E.; Burke, Allison E.; Nielsen, Charlotte; Hannam, Joshua J.; Bauer, Leah S. 2008. Nondormancy in Entomophaga maimaiga azygospores: effects of isolate and cold exposure. Mycologia. 100(6): 833-842.

Hajek, Ann E.; Wheeler, Micheal M.; Eastburn, Callie C.; Bauer, Leah S. 2001. Storage of resting spores of the gypsy moth fungal pathogen, Entomophaga maimaiga. Biocontrol Science and Technology. 11: 637-647.

Hajek, A. E.; Bauer, L.; McManus, M. L.; Wheeler, M. M. 1998. Distribution of resting spores of the Lymantria dispar pathogen Entomophaga maimaiga in soil and on bark. BioControl 43:189-200

Smitley, D. R.; Bauer, L. S.; Hajek, A. E.; Sapio, F. J.; Humber, R. A. 1995. Introduction and establishment of Entomophaga maimaiga, a fungal pathogen of gypsy moth (Lepidoptera: Lymantriidae) in Michigan. Environmental Entomology 24(6):1685-1695

Research Participants

Principal Investigators

Last Modified: November 27, 2018