Bathyplectes parasitoids (Hymenoptera: Ichneumonidae) of alfalfa weevil, Hypera postica, (Coleoptera: Curculionidae) in Wyoming
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Six sites were surveyed for Bathyplectes parasitoids (Hymenoptera: Ichneumonidae) of alfalfa weevil, Hypera postica (Gyllenhal) (Coleoptera: Curculionidae), to compare parasitism rates across Wyoming and among Bathyplectes spp. Fourth instars of alfalfa weevil were collected and reared individually until a weevil or parasitoid (adult or pupa) emerged. Though relative rates of parasitism for the two most prevalent species (B. curculionis [Thomson] and B. stenostigma [Thomson]) differed among survey sites, the rank order of parasitoids (species prevalence) was consistent across survey sites and three survey years. Of a total of 4,463 weevils assessed, parasitism rates of B. curculionis (mean = 34.5%) > parasitism rates of B. stenostigma (mean = 3.7%) > parasitism rates of B. anurus [Thomson] (mean = 0.045%). The range of B. curculionis parasitism rates (7.4 to 65.3%) was similar to that reported before the last release effort involving B. anurus that occurred in the 1980's. B. stenostigma was present at all sites, but at low densities: parasitism rates ranged from 0.2 to 16.9%. B. anurus was uncommon, and contributed little to the overall larval parasitism of alfalfa weevil in Wyoming, despite the substantial release effort in the 1980's. Earlier reports of B. curculionis dominance in the western U.S., and the relative scarcity and ineffectiveness of B. anurus in Wyoming were supported by our data.
