Progress 10/01/00 to 09/30/06
Outputs
This project focused on two important aspects of gypsy moth population dynamics. One concerns the fungal pathogen of gypsy moth, Entomophaga maimaiga, that has been known for many years in Japan, but appeared unexpectedly in North America in 1989. Since that time, E. maimaiga has completely altered the dynamics of gypsy moth in the northeast and made gypsy moth outbreaks much less common than they were. Our research is focused on the question of why the strain of E. maimaiga in North America has been so effective and successful, whereas earlier attempts to introduce E. maimaiga from Japan did not result in any establishment. In laboratory tests we compared the virulence and pathogenicity of E. maimaiga isolates derived from North America with those collected in Japan. We also tested the performance of E. maimiaga from Japan on Japanese gypsy moths that were being reared in quarantine in Hamden CT. Although, North American isolates are similar in virulence and
pathogenicity to those from Japan, North American gypsy moths were more susceptible than Japanese gypsy moths to E. maimaiga from either North America or Japan. As part of this work, we realized that there is great confusion in the literature concerning the definitions of virulence and pathogenicity, so we wrote a review article that attempts to clarify this confusion. In 2006 documented a major epizootic of the fungal pathogen Entomophaga maimaiga in low density populations of gypsy moth in western Massachusetts. Even though gypsy moth populations resurged across the northeast n 2005-2006 threatening the first major outbreak since 1981, our data suggest that E. maimaiga caused high levels of mortality and prevented widespread defoliation in most areas We completed our study of the curious behavioral change associated with gypsy moth larvae from high density populations, whereby they remain in the canopy of trees and feed day and night in contrast to larvae from low density
populations that seek daytime resting locations on the forest floor at the base of trees. These changes in behavior are important to population dynamics because they determine the relative impact of parasitoids and avian predators, which are active in the tree canopies, compared with invertebrate and small mammal predators which are active on the forest floor. We developed a laboratory bioassay of this behavioral change, and demonstrated that the daily migration only occurs if lights dim gradually. Instantaneous lights on or off failed to trigger migration. These finding have implications for anyone who studies daily rhythms of animal behavior in a laboratory setting, where the day and night are determined by lights that typically go on and off instantaneously. With this bioassay system, we found evidence that crowding of larval gyspy moths may cause the cessation of migration in high density populations, but that maternal effects in the form of eggs collected from low and high
density populations had no effect of the migratory propensity of larvae reared from those eggs.
Impacts
Our research helps explain why gypsy moth, which used to be the most important forest defoliator in the eastern United States, now has become a minor pest because outbreaks are much less frequent.
Publications
- No publications reported this period
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Progress 10/01/04 to 09/30/05
Outputs
Gypsy moth populations are resurging across the northeast and we expect a major outbreak for the first time since 1981. We are collecting data on the incidence of Entomophaga maimaiga, a fungal pathogen of gypsy moth that either will or will not cause the decline of outbreak populations. We are also studying the interaction between gypsy moth and winter moth, Operophtera brumata, a new European invader that is causing defoliation of many deciduous trees in eastern Massachusetts. Winter moth, gypsy moth, and another forest defoliator, the forest tent caterpillar, are all in outbreak densities in southeastern Massachusetts. We are estimating densities of gypsy moths and other lepidoptera in sites with and without winter moth to see if the presence of the former influences densities of these other species.
Impacts
The research enables us to predict whether gypsy moth is likely to resurge again as a major defoliator of forest trees in our region, or whether it is likely to remain as a very infrequent pest.
Publications
- Thomas, S. 2005. Pathogenicity and virulence of Entomophaga maimaiga, (Entomophthorales: Entomophthoracae), a fungal pathogen of gypsy moth, Lymantria dispar L.(Lepidoptera: Lymantriidae). Ph. D. dissertation, University of Massachusetts.
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Progress 10/01/03 to 09/30/04
Outputs
We continued our research this year on the fungal pathogen of gypsy moth, Entomophaga maimaiga, that has been known for many years in Japan, but appeared unexpectedly in North America in 1989. Since that time, E. maimaiga has completely altered the dynamics of gypsy moth in the northeast and made gypsy moth outbreaks much less common than they were. Our research is focused on the question of why the strain of E. maimaiga in North America has been so effective and successful, whereas earlier attempts to introduce E. maimaiga from Japan did not result in any establishment. In laboratory tests we have compared the virulence and pathogenicity of E. maimaiga isolates derived from North America with those collected in Japan. Last year we tested the performance of E. maimiaga from Japan on Japanese gypsy moths that were being reared in quarantine in Hamden CT. Although, North American isolates are similar in virulence and pathogenicity to those from Japan, North American
gypsy moths were more susceptible than Japanese gypsy moths to E. maimaiga from either North America or Japan. This year we completed an experiment aimed at selecting lines of E. maimaiga for higher virulence. We selected fast replicating vs slow replicating lines of E. maimaiga within a host. After five rounds of selection for increased growth within the host, there was no significant difference in replication rate of the pathogen; however, both proportion killed and speed of kill increased as measured with injection bioassays. In addition, there were decreases in pathogenicity in some of the lines when a dipping bioassay was performed.
Impacts
The research enables us to predict whether gypsy moth is likely to resurge again as a major defoliator of forest trees in our region, or whether it is likely to remain as a very infrequent pest.
Publications
- Elkinton, J. S., A. M. Liebhold and R.M. Muzika 2004. Effects of alternate prey on predation by small mammals on gypsy moth pupae. Population Ecology 46: 171-178.
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Progress 10/01/02 to 09/30/03
Outputs
We continued our focus this year on two important aspects of gypsy moth population dynamics. One concerns the fungal pathogen of gypsy moth, Entomophaga maimaiga, that has been known for many years in Japan, but appeared unexpectedly in North America in 1989. Since that time, E. maimaiga has completely altered the dynamics of gypsy moth in the northeast and made gypsy moth outbreaks much less common than they were. Our research is focused on the question of why the strain of E. maimaiga in North America has been so effective and successful, whereas earlier attempts to introduce E. maimaiga from Japan did not result in any establishment. In laboratory tests we have compared the virulence and pathogenicity of E. maimaiga isolates derived from North America with those collected in Japan. This year we also tested the performance of E. maimiaga from Japan on Japanese gypsy moths that were being reared in quarantine in Hamden CT. Although, North American isolates are
similar in virulence and pathogenicity to those from Japan, North American gypsy moths were more susceptible than Japanese gypsy moths to E. maimaiga from either North America or Japan. As part of this work, we realized that there is great confusion in the literature concerning the definitions of virulence and pathogenicity, so we wrote a review article that attempts to clarify this confusion. We completed our study of the curious behavioral change associated with gypsy moth larvae from high density populations, whereby they remain in the canopy of trees and feed day and night in contrast to larvae from low density populations that seek daytime resting locations on the forest floor at the base of trees. These changes in behavior are important to population dynamics because they determine the relative impact of parasitoids and avian predators, which are active in the tree canopies, compared with invertebrate and small mammal predators which are active on the forest floor. We developed
a laboratory bioassay of this behavioral change, and demonstrated that the daily migration only occurs if lights dim gradually. Instantaneous lights on or off failed to trigger migration. These finding have implications for anyone who studies daily rhythms of animal behavior in a laboratory setting, where the day and night are determined by lights that typically go on and off instantaneously. With this bioassay system, we found evidence that crowding of larval gyspy moths may cause the cessation of migration in high density populations, but that maternal effects in the form of eggs collected from low and high density populations had no effect of the migratory propensity of larvae reared from those eggs.
Impacts
The research enables us to predict whether gypsy moth is likely to resurge again as a major defoliator of forest trees in our region, or whether it is likely to remain as a very infrequent pest.
Publications
- Garcia-Bailo, Bibiana. 2003. Vertical migration of late-instar larval gypsy moths, Lymantria dispar L. Master thesis, University of Massachusetts, Amherst.
- Thomas, S. R. and J. S. Elkinton. 2004. Pathogenicity and virulence. Journal of Invertebrate Pathology (submitted).
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Progress 10/01/01 to 09/30/02
Outputs
We focused research this year on two important aspects of gypsy moth population dynamics. One concerns the fungal pathogen of gypsy moth, Entomophaga maimaiga, that has been known for many years in Japan, but appeared unexpectedly in North America in 1989. Since that time E. maimaiga has completely altered the dynamics of gypsy moth in the northeast and made gypsy moth outbreaks much less common than they were. Our research is focused on the question of why the strain of E. maimaiga in North America has been so effective and successful, whereas earlier attempts to introduce E. maimaiga from Japan did not result in any establishment. In laboratory tests we have compared the virulence of E. maimaiga isolates derived from North America with those collected in Japan. Thus far, there is no evidence that North American isolates are any more or less virulent than those from Japan. We are currently engaged in selection experiments to see if it is possible for the virulence to
change over time. Another aspect of gypsy moth population dynamics concerns the curious behavioral change associated with larvae from high density populations, whereby they remain in the canopy of trees aand feed day and night in contrast to larvae from low density populations that seek daytime resting locations on the forest floor at the base of trees. These changes in behavior are important to population dynamics because they determine the relative impact of parasitoids and avian predators, which are active in the tree canopies, compared with invertebrate and small mammal predators which are active on the forest floor. We have developed a laboratory bioassay of this behavior, which will allow us to explore the mechanisms that govern this shift in behavior. Graduate students on this project = 2.
Impacts
The research enables us to predict whether gypsy moth is likely to resurge again as a major defoliator of forest trees in our region, or whether it is likely to remain as a very infrequent pest.
Publications
- Cooper, V. S., M. H. Reiskind, J. A. Miller, K. Shelton, B. A. Walther, E. J. Temeles, J. S. Elkinton+, and P. W. Ewald 2002. Timing of transmission and the evolution of virulence of an insect virus. Proc. Royal Soc B, London 269: 1161-1165
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Progress 10/01/00 to 09/30/01
Outputs
We have continued gypsy moth egg mass counts at sites on Cape Cod and near the Quabbin reservoir in western Massachusetts. We continue to conduct burlap counts of larvae and to assess them for the fungal pathogen, Entomophaga maimaiga. We will conduct comparative work with the browntail moth, Euproctis chrysorrhoea, on Cape Cod. The long time series we have amassed of year to year changes in gypsy moth density should allow analyses that provide important insight into the dynamics of the gypsy moth system.
Impacts
To be able to predict gypsy moth outbreaks at least a year or two before they occur.
Publications
- Liebhold, A. M., J. S. Elkinton, D. Williams, and R. M. Muzika What causes outbreaks of gypsy moth in North America? Population Ecology 2000 42:257-266.
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