Paradoxes of Poweshiek Skipperling (Oarisma poweshiek) (Lepidoptera: Hesperiidae): Abundance Patterns and Management of a Highly Imperiled Prairie Species

Although Oarisma poweshiek sometimes occurred in localized abundance, its known range is centered on the highly decimated northern tallgrass prairie of North America. To aid its conservation, we analyze surveys from 1988 to 1997 of populations no longer being found. While we recorded 2403 individuals at 20 sites, five sites had 87% of individuals, while 12 sites had only 2% of individuals. Most surveys during O. poweshiek flight had zero individuals recorded. In peak vegetative characteristics for O. poweshiek, fire management had the highest mean abundance but the lowest median abundance and lowest percent occurrence compared to idling and haying. Mean abundance was by far the lowest in the first year postfire compared to longer since fire. Median abundance and percent unit surveys where O. poweshiek was found indicated higher abundances the longer since fire. Although this skipper occasionally exhibited super-recoveries after fire, the median result in fire-managed occupied sites was zero. In a few years, abundance appeared synchronized across many sites, either low (1993, 1997) or high (1994-1995). It is only through a constant focus on avoiding the worst-case scenario that the rare best-case scenario of long-term population persistence appears possible for O. poweshiek. 1. Introduction Oarisma poweshiek (Poweshiek skipperling) (Lepidoptera: Hesperiidae) is specialized to native herbaceous flora, with a relatively small range centered on northern tallgrass prairie in North America from eastern Wisconsin to Iowa, Minnesota, the eastern Dakotas, and southeastern Manitoba, as well as populations in fen wetlands in the lower peninsula of Michigan [1–6]. Reported caterpillar food plants include dominant but finer threadlike grasses of tallgrass prairie such as Sporobolus heterolepis (prairie dropseed), Schizachyrium scoparium (little bluestem), Bouteloua curtipendula (sideoats grama), and the coarser Sorghastrum nutans (Indian grass), as well as Carex (sedges) and Eleocharis elliptica (spike-rush) primarily for the Michigan populations [6–11]. However, little research is available to confirm larval host plants in the field in much of its range. Since European contact in North America, tallgrass prairie has been about 99% destroyed in most central North American states and provinces, primarily for conversion to agriculture, with never-tilled prairie fragments remaining in preserves, parks, and unintensively utilized farmland [12, 13]. As a result, this skipper has been of conservation concern for decades as evidenced by [11, 14–20] with decades of