A ten-year study of the status and trend of the regal fritillary (Speyeria idalia) (Lepidoptera: Nymphalidae) in Wisconsin, U.S.A.

Abstract

We summarize all available locality records by us and others for the regai fritillary (Speyeria idalia) during 1970-99 in Wisconsin, where it is listed as endangered. Nearly all areas of regular observation (i.e., populations) occurred in clusters of sites. All historical localities and extant populations (or population clusters) were discovered by volunteers. The species' historical reputation as localized and scarce continues to appear justified, but the paucity of historical data precludes further refinement of its statewide status and trend in past decades. Regal fritillary habitat has typically been described as native prairie grassland. This appears often, but not always, to correlate with other factors more strongly associated with regal fritillary populations: larger grassland patches more likely to have topographic diversity and long-term histories of more favorable land uses (such that native flora, if present, has not been destroyed). These other factors, without regard for the "nativeness" of the vegetation, have proven useful in selecting sites to search for undiscovered populations. We also present analyses of our transect survey data from 49 grasslands in Wisconsin during 1990-99 for both regal fritillary and the closely related but more widespread and abundant Aphrodite fritillary (Speyeria aphrodite). Flight period timing varied among years by >3 weeks for both fritillaries. These results should be useful for designing and interpreting surveys to monitor fritillary populations.