Relationships between Army Cutworm Moths and Grizzly Bear Conservation
AuthorRobison, Hillary Lindsay
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Army cutworm moths (Euxoa auxiliaris) are native to North America and are both agricultural pests and an important food for grizzly bears (Ursus arctos horribilis). The moths migrate from low elevations in the Great Plains and Intermountain West to high elevations in the Rocky Mountains where they aggregate in talus and are consumed by bears by the millions during summer.There are conservation implications of moths as food for bears. Previous studies determined the moths are the richest bear food in the Greater Yellowstone Ecosystem (GYE). Bears that gorge on moths can consume half of their yearly energy in about 30 days. Moths occur in remote areas rarely visited by humans and are available through autumn. When high elevation foods like moths and whitebark pine (Pinus albicaulis) seeds are abundant, bears forage for them in these remote areas. The availability of food in autumn influences bear litter size. When these foods fail, bears forage widely and get into more fatal conflicts with humans. Human-caused bear mortality is the major threat to bears. Balancing recruitment and mortality is essential to bear conservation.Research on the moths is critical to understanding their availability to bears and their roles in ecosystems. I reviewed literature about the moth's ecology and its interaction with bears. I then describe research that may advance our understanding of this interaction. The moth's migration is unusual. It migrates across latitudes whereas most other pestiferous moths in North America migrate latitudinally. Migration across latitudes appears to be easier than migration across longitudes, but how these moths determine longitude is unknown. The moth's migration and reproductive activity were thought to be incompatible, but I found that this is not the case.I investigated population structure in the moth using microsatellites so I might describe more clearly their migration and the scale at which it may influence their availability to bears. The results indicate the moths are panmictic. This is favorable for the long-term persistence of the interaction between moths and bears. Population structure, indicative of site fidelity, would make the moths susceptible to local perturbations at low elevations and likely result in corresponding extirpations at high elevation sites. The Rocky Mountains appear not to be a barrier, and the moths may migrate from the west to the mountains as well as from the east.I studied whether moths, whose larvae may be sprayed with organochlorine, organophosphate and pyrethroid pesticides, contain chemical residues which could be toxic to bears or bioaccumulate in bears. The results of these analyses show that moths contain very low levels of contaminants, but these levels are unlikely to be toxic to or bioaccumulate in bears.I modeled moth and bear habitat using geospatial variables extracted from locations where bears forage for moths. Elevation, geology, and Landsat TM imagery describe areas currently used by moths and bears in the GYE and predict areas which may be suitable for moths and into which bears may expand within the GYE. Slope, aspect, and heat-load also were significant predictors of these sites but did not contribute as much to model fit to the data. The model may reflect bear preferences for foraging for moths more than the distribution of moths in high elevations because the data used to generate the model are based on locations where bears feed on moths, not on moth locations alone.