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Grizzly bears (Ursus arctos horribilis) consume adult army cutworm moths (Euxoa auxiliaris) from late June through mid-September on alpine talus slopes in Glacier National Park (GNP), Montana. As part of a study carried out to better understand the ecological interactions between grizzly bears and army cutworm moths in GNP, we studied temporal abundance patterns, body mass and composition, and migration potential of moths collected from alpine moth aggregation sites throughout the summer of 1994 and 1995. Army cutworm moths arrived in the alpine zone of GNP in late June or early July and departed by late August or early September. While moths were in the alpine zone, their body mass and moisture, lipid, and gross energy contents markedly increased and crude protein decreased. The absence of moths from the alpine zone coincided with the presence of moths on the Great Plains. Using published estimates of the cost of transport in flying animals, we calculated that an army cutworm moth flying in late summer through still air could fly 140 km using body lipid reserves alone.

Grizzly bears (Ursus arctos horribilis) consume army cutworm moths (Euxoa auxiliaris) from late June through mid-September at alpine moth aggregation sites in Glacier National Park, Montana. To better understand the importance of army cutworm moths to grizzly bears, we determined the sex and age classes and minimum numbers of grizzly bears foraging at known alpine moth aggregation sites, and documented the timing and use patterns of grizzly bears foraging in these areas. A minimum of 36 grizzly bears were observed 106 times feeding at 6 of 9 known moth aggregation sites from late June through mid-September in 1992-1995; no bears were observed on moth sites in 1993. Bears fed on moth aggregations disproportionately more at elevations >2561 m, on slopes between 31° and 45°, and on southwest-facing aspects. Lone adult grizzly bears appeared to be underrepresented and subadults overrepresented at moth sites. Moths are highly digestible; all parts are digested except for the exoskeleton. We propose that army cutworm moths are an important, high-quality, preferred summer and early-fall food for grizzly bears in Glacier National Park. We do not present any data that demonstrate an increase in the importance of moths when other foods fail.

Bears (Ursidae) were observed from fixed-wing aircraft on or near alpine talus in the Shoshone National Forest between 15 June and 15 September in 1981–1989. Bears fed on insect aggregations at 6 known and 12 suspected alpine talus sites, disproportionately more at elevations > 3350 m, on slopes > 30°, and on south- and west-facing aspects. While at these sites, bears almost exclusively ate invertebrates, typically army cutworm moths (Euxoa auxiliaris). Subadult grizzly bears (Ursus arctos horribilis) appeared to be underrepresented at the sites, and proportionate representation of adult females with young appeared to decrease between 15 June and 15 September. Overall, observations of bears at these sites increased between 1981 and 1989. We suggest that alpine insect aggregations are an important food source for bears in the Shoshone National Forest, especially in the absence of high-quality foraging alternatives in July and August of most years.

An air drying and Giemsa staining technique produces consistently good quality cytological preparations when applied to different species of Euxoa (Lepidoptera: Noctuidae) and, in particular, it allows an improved resolution of the meiotic chromosomes in both sexes. All species so far investigated have a basic haploid chromosome complement of n(♀) = 31(XX); n(♂) = (XY). A single chiasma per individual bivalent is clearly visible in the male sex. Some chiasmata are formed in interstitial positions, but, by metaphase I, they have all undergone complete terminalization while the bivalents orient axially on the first division spindle. Direct evidence for lack of chiasma formation in the 31 hormorphic bivalents in the female sex is reported for the first time for species of Noctuidae. Evidence in favor of an XY system in the female sex is discussed. Preliminary studies of the meiotic divisions in hybrid material reveal the presence of cryptic structural differences between certain taxa, and will help to elucidate taxonomic problems within this complex genus.