Life history of an endangered prairie butterfly: insights from an ex situ population of Poweshiek skipperling in Manitoba, Canada

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Eckhardt, Kirstyn
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Species recovery plans benefit from a complete understanding of an organism’s biology. The Poweshiek skipperling, Oarisma poweshiek (Parker) (Lepidoptera: Hesperiidae), is an endangered butterfly native to tallgrass prairies in North America. Following rapid, range-wide population crashes, Poweshiek are now reared ex situ in Manitoba, Canada to augment the remaining wild population. Although this species has been the focus of research since their “Endangered” listing in 2014, there are knowledge gaps regarding Poweshiek skipperling life history. I measured head capsule widths of larvae of two Poweshiek cohorts to determine the overwintering instar. I analysed six years of ex situ data to assess trends in the timing of flight period, degree day accumulations, and protandry. I estimated this species’ lower developmental threshold using dates for developmental milestones. Head capsule measurements showed that Poweshiek typically overwinter in the fourth instar. Peak flight period varied among years by up to three weeks, while degree day accumulations were similar between years. I found evidence that this species is protandrous. An information theoretical approach using Akaike Information Criterion was used to assess lower developmental thresholds. This approach indicated different lower developmental thresholds for larvae and pupae; the AICc scores also demonstrated that larvae enter winter dormancy at different stages of development. These findings will inform conservation decision-making and may allow for greater accuracy in predicting the adult flight period.
Endangered species, Poweshiek skipperling, Ex situ rearing, Butterfly conservation, Head capsule, Degree days, Developmental threshold