Endangered black-footed ferrets: Field testing fipronil bait pellets (FipBits) to prevent plague
Principle Investigators
Dr. Magnus McCaffrey, Turner Institute of Ecoagriculture
Randy Matchett, US Fish and Wildlife Service, Charles M. Russell National Wildlife Refuge (CMR)
Rationale.
The purpose of this project is to produce and conduct field evaluation of a promising new management tool, bait pellets containing fipronil (FipBits), for mitigating the impact of plague in prairie dog and ferret populations. Plague is the primary biological challenge to black-footed ferret recovery. Thus, developing and implementing effective plague management tools is essential for downlisting and delisting of this endangered species. Existing methods of flea control (plague vector) – e.g., deltamethrin dust, fipronil grain, or sylvatic plague vaccine (SPV) – have limitations. A new fipronil-based bait alternative may offer an efficient and more cost-effective option. Treatment of prairie-dog colonies by distributing 0.25 to 0.5 cups of grain (wheat) treated with 0.005% fipronil at each prairie-dog burrow has proven highly effective for flea control, but expensive. USFWS biologist, Randy Matchett, has invented a novel fipronil-based bait pellet (FipBits), whereby small amounts of fipronil are combined with inexpensive, food-grade ingredients in a pellet readily consumed by prairie dogs. By coupling mass-production with low-cost, practical, and efficient bait-pellet distribution technologies, FipBitsare showing strong potential to substantially reduce flea-control costs. FipBits have been evaluated on small test plots in South Dakota, Montana, and Arizona, where near-complete flea control was achieved one-year post-FipBit treatment on most plots and in some cases, two years post-treatment. Follow-up work, using fipronil as well as other insecticides, at larger scales supported these findings, with effective flea control persisting up to 12 months post–treatment. These findings are highly encouraging and underscore the potential utility of FipBits for controlling the primary vector of plague in prairie-dog and ferret populations. Expanded field trials in conjunction with operational use of FipBitsare needed. This research aims to continueFipBit evaluation on black-tailed prairie dogs at Bad River Ranches in South Dakota, and to expand FipBit evaluations to Gunnison’s prairie dogs on Vermejo Park Ranch as part of a collaborative effort to evaluate if larger-scale and widespread FipBit treatments have the same or better level of plague prevention in comparison to more expensive treatments. If FipBit effectiveness can be demonstrated through these field trials and operational use, FipBits could dramatically improve plague-mitigation efforts and consequently significantly advance ferret recovery.
Outcomes.
The flea-borne agent of plague, Yersinia pestis, is lethal to endangered black-footed ferrets (BFFs) and the prairie dogs (PDs) on which BFFs depend for habitat and prey. We developed bait pellets containing insecticides for flea control with PDs. Individual baits contained 0.46, 0.91, 1.21, or 1.52 mg fipronil, 5.40 mg afoxolaner, 50.62 mg fluralaner, or 85.20 mg spinosad. From 2023 to 2025, we tested the baits with black-tailed PDs (BTPDs), Gunnison’s PDs (GPDs), and Richardson’s ground squirrels (RGSs). We sampled hosts 2810 times and detected 8825 fleas across 2 U.S. States, 1 Canadian Province, 6 sites, 9 PD colonies, and 41 sampling plots. Over ~12 mo across 5 replicates in South Dakota, USA, bait pellets with 0.91 or 1.52 mg fipronil, applied at a rate of 125 baits/ha, were more effective in reducing the abundance of fleas on BTPDs than 0.46 mg fipronil or the 3 other active ingredients; on 2 South Dakota replicates with data from 24 mo posttreatment, the effects of fipronil pellets on flea abundance had waned after ~24 mo. Similarly, over ~12 mo on 2 replicates in Arizona, USA, pellets with 1.52 mg fipronil were more effective in reducing the abundance of fleas on GPDs than pellets with 0.46 mg fipronil; on 1 replicate with available data from ~2 yr posttreatment, the effects of fipronil pellets had waned after ~24 mo. Over ~8-11 mo across 2 replicates in Saskatchewan, Canada, baits with 1.21 mg fipronil/pellet were more effective in suppressing the abundance of fleas on BTPDs and RGSs when applied at 250 pellets/ha than 62 pellets/ha; flea control had waned after ~20-23 mo. When applied annually at 125-250/ha, baits with 0.84-1.52 mg fipronil (FipBits) provided an effective, efficient, and affordable tool for flea control on PD colonies. Assessment work continues.
Eads, D., M.R. Matchett, M. McCaffery, A. Hemmah, A. Jarding, J. Cordova, H. Heimann, S. Liccioli, L.E. Gardiner, J. Cormack, H. Hicks, J. Fly, E. Childers, T.M. Livieri, M.L. Hladik, D.E. Biggins. 2026. Edible baits for systemic flea control, plague mitigation, and wildlife conservation: evaluation of four active ingredients with three rodent species in western North America. International Journal for Parasitology. doi.org/10.1016/j.ijppaw.2026.101216
