Herbicide treatment to restore St. Anthony Dune tiger beetle habitat: a pilot study

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This paper reports results of a vegetation management pilot test to benefit St. Anthony Dune tiger beetles (Cicindela arenicola Rumpp [Idaho dunes tiger beetle]) at Minidoka National Wildlife Refuge (NWR) in southern Idaho. C. arenicola is listed as a critically imperiled/imperiled species by NatureServe (2008). In the Idaho Comprehensive Wildlife Conservation Strategy (2008), C. arenicola is listed as a species of conservation need (imperiled). C. arenicola were located on the refuge in small remnant sand dunes in the mid-1990s. Opportunistic searches since that time have not detected any C. arenicola on the refuge. The dunes there visually appeared to become more overgrown with the invasive annual grass, downy brome (Bromus tectorum L). Comparison of USGS aerial photographs from the mid-1950s with current conditions (Google Earth 2008) suggests that vegetation encroachment on the dunes has reduced tiger beetle habitat on Minidoka NWR. To improve beetle habitat, a pilot study was conducted with an herbicide application to reduce downy brome density. Imazapic (Plateau®) was selected because of its effectiveness against downy brome, minimal effects on native vegetation, and a relatively low toxicity to all animals. Surveying plots, the authors found that the pilot test was successful in reducing downy brome and therefore could have widespread applicability in habitat management. They then decided to conduct a bioassay to test for direct effects of the herbicide on the beetles. Negative effects would negate the herbicides as a potential habitat management tool. A simple laboratory bioassay was performed to study the effects of both imazapic and glyphosate (Touchdown®) on a species of tiger beetle because both have the potential to manage habitats for dune tiger beetles. Together they can effectively remove invasive plants, and glyphosate has been used to successfully assist in establishing native plant species. Because C. arenicola is a species of conservation concern, C. repanda Dejean was used in this study as a surrogate tiger beetle. Little research exists for imazapic-insect interactions; however, there is a body of literature for glyphosate-insect interactions. In the present study, no direct effect of either herbicide was noted on the beetles; however, indirect effects were not investigated. Additional research and future searches for C. arenicola will be needed to determine the success of the potential management strategies presented.

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ELECTRONIC FILE - Zoology

Please note: this document might have come out as late as 2009. It is not dated and the TWO copies we have were saved on the morning of 1/5/2009 and the night of 3/14/2009, the latter version having status codes. The field work was completed in 2008. UPDATE: Some version of this report was published in the journal Cicindela (May 2009, vol. 41, no.1, pp. 13-24). That article should be obtained and cited rather than these Word docs.