Mitigating plague risk in utah prairie dogs: Evaluation of a systemic flea-control product

Plague, the disease caused by the bacterium Yersinia pestis, is a major threat to the Utah prairie dog (Cynomys parvidens), a species listed as threatened under the U.S. Endangered Species Act. Fleas are the primary vectors of plague, and flea control can stop the spread of plague epizootics and increase Utah prairie dog survival. We evaluated a newly developed grain-bait insecticide treated with the active ingredient imidacloprid. In 2009, we conducted a single application of the product in treatment plots within each of 4 study sites and sampled fleas from captured Utah prairie dogs on treatment and control plots at monthly intervals. We observed mixed results; the product generally was effective at reducing flea prevalence, abundance, and intensity on prairie dogs at some sites and not at others, and the effectiveness within a site varied over time. In 2010, we doubled the amount of bait on treatment plots, yet we still failed to observe a consistent decline in flea prevalence, abundance, and intensity on prairie dogs. At the application rates we evaluated, the imidacloprid product is likely not as effective at controlling fleas on Utah prairie dogs as the more commonly used topical insecticide containing deltamethrin. However, managers should also consider the risk of flea species developing resistance following the repeated application of a single flea-control product. Furthermore, because we observed a higher than expected diversity of flea species (8) on Utah prairie dogs, future work should be undertaken to investigate how other mammalian host species might mediate flea population dynamics, plague ecology, and the outcome of flea management approaches.