Potential Causes of Declines in Minnesota’s Prairie Butterflies with a Focus on Insecticidal Control of the Soybean Aphid

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Potential Causes of Declines in Minnesota’s Prairie Butterflies with a Focus on Insecticidal Control of the Soybean Aphid

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2017-03-20

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Minnesota Invasive Terrestrial Plants and Pests Center, University of Minnesota

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Abstract

Minnesota is home to diverse prairie butterfly fauna, but several species have recently undergone drastic population declines. For example, 10 of the 15 butterfly species classified as Endangered, Threatened, and of Special Concern by the State of Minnesota depend exclusively on native prairies. The declines of two of these, the Dakota Skipper and the Poweshiek Skipperling, have been so precipitous that they are now exceedingly rare despite having been predictably common previously. Poweshiek Skipperling is now on the verge of global extinction. Multiple regional and local factors may have contributed to these declines, and those factors are expected to have interacted in various ways. However, a working hypothesis is that these butterfly declines are at least in part the result of insecticide drift related to management of the soybean aphid, which invaded Minnesota in 2000 and led to substantial increases in insecticide applications to soybeans. On November 15, 2016, the Minnesota Invasive Terrestrial Plants and Pests Center (MITPPC) in collaboration with the University of Minnesota Institute on the Environment held a workshop to assess hypotheses that could explain the butterfly declines. The workshop featured seven speakers from the US Fish and Wildlife Service, Minnesota Department of Natural Resources, Minnesota Zoo, University of Minnesota, and Environmental Protection Agency. The presentations, which MITPPC has posted online (http://z.umn.edu/mitppcbutterfly), focused on three themes: (i) biology and conservation status of the endangered butterflies, (ii) the possible role of soybean aphid management in affecting butterfly populations, and (iii) risk assessment and potential solutions via conservation measures. The workshop fostered collaboration between experts in prairie conservation and agricultural pest management and featured extensive discussion between participants following the presentations. Members of the conservation and agricultural communities are typically not afforded the chance to engage in conversations of this type and discussions were particularly fruitful for information sharing and relationship building. This document synthesizes the findings of the workshop and provides guidance to the MITPPC on a needed integrative research program studying the non-target consequences of invasive soybean aphid management on Minnesota’s endangered prairie butterflies. We conclude that skipper conservation will be advanced through a new research program that includes tests of the hypothesis that soybean aphid insecticides are contributing to skipper declines. Targeted research is needed to assess 1) the extent of insecticide exposure the butterflies may experience in the wild and 2) the biological consequences of those exposures using replicated controlled experiments. Ongoing drift studies conducted by the Minnesota Zoo and US Fish and Wildlife Service (see below) have provided important preliminary links to soybean aphid insecticides, but significantly more data is needed to really understand wild exposure dynamics. Controlled exposure experiments may soon be launched by Minnesota Zoo and University of Minnesota researchers, but those experiments are currently funding- and personnel-limited and cannot address the full range of needed tests. The MITPPC can play a leading role by supporting and expanding critical comprehensive research on potential non-target effects of management against an invasive pest.

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Minnesota Invasive Terrestrial Plants and Pests Center, Institute on the Environment

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Runquist, Erik; Heimpel, George E.. (2017). Potential Causes of Declines in Minnesota’s Prairie Butterflies with a Focus on Insecticidal Control of the Soybean Aphid. Retrieved from the University Digital Conservancy, https://hdl.handle.net/11299/254600.

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