Evaluation of Five Pulicides to Suppress Fleas on Black-Tailed Prairie Dogs: Encouraging Long-Term Results with Systemic 0.005% Fipronil.

Plague, a flea-borne disease, hampers efforts to restore populations of black-footed ferrets (Mustela nigripes), which occupy colonies of prairie dogs (Cynomys spp.) in North America. Plague is managed by infusing prairie dog burrows with DeltaDust® 0.05% deltamethrin, a pulicide that kills fleas. Experiments are needed to identify pulicides that can be used in rotation with DeltaDust for integrated plague management. In South Dakota, USA, we tested the efficacy of four pulicide dusts when applied at a rate of 8 g per burrow on colonies of black-tailed prairie dogs (Cynomys ludovicianus): Sevin® 5% carbaryl; Dusta-cide® 6% malathion; Alpine® 0.25% dinotefuran with 95% diatomaceous earth; and Tri-Die® 1% pyrethrum with 40% amorphous silica and 10% piperonyl butoxide. We also tested systemic 0.005% fipronil, which was distributed as ½ cup of laced grain per burrow. We sampled prairie dogs on 3294 occasions and detected 10,041 fleas. Sevin and Dusta-cide suppressed fleas but only for 1 month. Neither Alpine nor Tri-Die had any noticeable, consistent effect on fleas. Fipronil suppressed fleas by 97-100% for 3 months. The residual effect of fipronil persisted for ∼12 months. Efficacy of fipronil seems comparable with DeltaDust, which exhibited a residual effect for ∼10 months in prior studies. Continued research is needed to optimize fipronil treatments for plague management on prairie dog colonies.

RESISTANCE TO DELTAMETHRIN IN PRAIRIE DOG ( CYNOMYS LUDOVICIANUS) FLEAS IN THE FIELD AND IN THE LABORATORY.

Sylvatic plague poses a substantial risk to black-tailed prairie dogs ( Cynomys ludovicianus) and their obligate predator, the black-footed ferret ( Mustela nigripes). The effects of plague on prairie dogs and ferrets are mitigated using a deltamethrin pulicide dust that reduces the spread of plague by killing fleas, the vector for the plague bacterium. In portions of Conata Basin, Buffalo Gap National Grassland, and Badlands National Park, South Dakota, US, 0.05% deltamethrin has been infused into prairie dog burrows on an annual basis since 2005. We aimed to determine if fleas ( Oropsylla hirsuta) in portions of the Conata Basin and Badlands National Park have evolved resistance to deltamethrin. We assessed flea prevalence, obtained by combing prairie dogs for fleas, as an indirect measure of resistance. Dusting was ineffective in two colonies treated with deltamethrin for >8 yr; flea prevalence rebounded within 1 mo of dusting. We used a bioassay that exposed fleas to deltamethrin to directly evaluate resistance. Fleas from colonies with >8 yr of exposure to deltamethrin exhibited survival rates that were 15% to 83% higher than fleas from sites that had never been dusted. All fleas were paralyzed or dead after 55 min. After removal from deltamethrin, 30% of fleas from the dusted colonies recovered, compared with 1% of fleas from the not-dusted sites. Thus, deltamethrin paralyzed fleas from colonies with long-term exposure to deltamethrin, but a substantial number of those fleas was resistant and recovered. Flea collections from live-trapped prairie dogs in Thunder Basin National Grassland, Wyoming, US, suggest that, in some cases, fleas might begin to develop a moderate level of resistance to deltamethrin after 5-6 yr of annual treatments. Restoration of black-footed ferrets and prairie dogs will rely on an adaptive, integrative approach to plague management, for instance involving the use of vaccines and rotating applications of insecticidal products with different active ingredients.