Ecological Effects of Deltamethrin Insecticide in

Abstract

In North America, plague is a relatively novel disease, causing many species to be highly to moderately susceptible to infection. The plague bacterium, Yersinia pestis, is spread between mammals by fleas (Siphonaptera), and, during an outbreak, causes entire prairie dog (Cynomys spp.) colonies to die off. These outbreaks are of particular conservation concern as they have slowed the recovery of the endangered black-footed ferret (Mustela nigripes) which feeds almost entirely on prairie dogs. In many areas where black-footed ferrets have been reintroduced, prairie dog colonies are treated with deltamethrin, a pytheroid insecticide that reduces flea populations and therefore reduces the spread of plague. Although this treatment has been successful at increasing survival of ferrets and prairie dogs while preventing outbreaks of the disease, little is known about the secondary effects of this treatment. I aimed to determine the effects of deltamethrin of non-target flea and arthropod populations to assess impacts to small mammals present on prairie dog colonies. Fleas, insects, and small mammals were assessed on prairie dog colonies at Wind Cave National Park, SD and Custer State Park, SD across six pairs of treated and untreated grids. In both 2013 and 2014, four small mammal trapping sessions occurred resulting in the capture of 146 and 280 deer mice (Peromuscus maniculatus) and the collection of 167 and 67 fleas respectively. Mouse fecal samples were collected from captured mice to analyze the consumption of arthropods and pit fall traps were placed throughout grids and opened for 3 sessions annually to assess the abundance of arthropods on the grids. Deltamethrin was shown to reduce the likelihood of flea infestation in mice on grids treated with deltamethrin in 2013 but not 2014 when overall infestation was low. Due to the large amounts of insects collected, specimens are still being identified to family. Three major beetle families, Scarabaeidae, Tenebrionidae and Carabidae, were pulled from 2014 samples and tallied. Scarabaeidae beetles were found in reduced numbers on treated grids, before the second annual treatment but returned to similar number after treatment. Fecal sample analysis revealed that deer mice on treated and untreated grids did not vary in their consumption of arthropods in either year. Analysis of mouse survival and population in frequentist and Bayesian frameworks revealed minimal to no change in mouse populations between treated and untreated areas as a small decline was noted in one session from one analysis. Overall, deltamethrin has a positive impact by reducing the fleas present on small mammals with minimal and non-lasting negative effects on arthropod populations. These effects did not impact mouse populations present on treated areas, supporting the use of deltamethrin. However, deltamethrin should be used with caution as minor declines observed in arthropod and mouse populations could be magnified with repeated uses. To maximize the benefits deltamethrin should be applied in years of high flea populations while forgoing treatment in low population years to reduce any negative impacts.