Evaluating the use of a low dose fipronil bait in reducing black-tailed prairie dog (Cynomys ludovicianus) fleas at reduced application rates

Abstract

Plague is a virulent zoonosis, vectored by fleas, posing danger to black-tailed prairie dogs (BTPDs) ( Cynomys ludovicianus ), black-footed ferrets ( Mustela nigripes ), and humans in North America. During prior research, a fipronil grain bait (0.005%) applied at rates of 1-½ cup/burrow, reduced flea abundance by > 95–100% when applied three times February–March in northern Colorado. The objective of the current study was to determine the efficacy of fipronil bait against fleas in northern Colorado at reduced application rates (½ cup/burrow) and frequencies (1–2 applications). The field study was conducted in Larimer county, Colorado USA between June-November 2018. Three test plots were selected: two treatment plots (1 vs. 2 fipronil bait applications) and one untreated control. Fipronil was applied at a rate of ½ cup (~95 g)/burrow. Fleas were collected from captured BTPDs and swabs of active burrows prior to bait application and up to 134-days post-treatment. A total of 203 BTPDs and 210 active burrows were sampled. Within the treatment plots, no fleas were collected from BTPDs up to 134-days post-treatment (100% efficacy). Five fleas were recovered from burrows within the one-application plot (<40-days post-application) with efficacy ranging from 97.1 to 100%. No fleas were recovered from burrows within the two-application plot. We caution that while fleas were present within the control plot throughout the study, abundances were low. The efficacy results are supported by those of prior field research conducted in South Dakota and suggest that fipronil bait may be applied at lower rates and frequencies than initially proposed, with potential to sustain flea removal >4-months.

Assembling a safe and effective toolbox for integrated flea control and plague mitigation: Fipronil experiments with prairie dogs

“…On average, fleas were less abundant on the site treated with ¼ cup FIP grain per burrow opening ( fleas per BTPD) than the site treated with ½ cup per burrow opening ( fleas; non-treated site = 1.14 fleas). In contrast to most prior experimental replicates [ 12 , 15 , 16 , 25 , 26 ], flea control was relatively ineffective.…”

“…We caution, while flea control was mostly effective during investigations of FIP grain treatments on BTPD colonies [ 12 , 15 , 16 , 25 ], results herein from Lower Brule, with late-May treatments, demonstrate that flea control with FIP grain can be variable. Perhaps the late-May period, when vegetation is growing and sometimes highly nutritious, is an inopportune time to complete FIP grain treatments.…”

“…When applying deltamethrin dust, ≥4 g could be infused into each burrow; previous research suggests 6–8 g is perhaps better than 4 g [ 23 ]. When applying FIP grain, ½ cup [ 15 , 16 ] or ¼ cup [ 25 ] could be distributed near each BTPD burrow opening, regardless of burrow activity. Effective flea control with FIP grain necessitates bait consumption by BTPDs.…”

“…Additional modes of flea exposure to FIP are possible, perhaps for multiple flea life-stages. FIP disrupts the flea central nervous system and blocks GABA A receptors, causing hyperexcitation, paralysis, and death [9][10][11][12][13][14][15][16]. In some cases, flea populations are controlled for up to 12 months or more, likely due to effects of FIP treatments on multiple flea life-stages [16].…”

Interrelationship of soil moisture and temperature to sylvatic plague cycle among prairie dogs in the Western United States

“…Eradication of flea infestation using insecticides was appreciated more than 50 years ago as a successful way to reduce the incidence of plague and is still in use today (Kartman & Hudson 1971;Poche et al 2020). However, plague epizootics have been recorded in areas with insecticide usage suggesting rapid resistance develops and/or that parameters other than total number of fleas are important in determining risk of outbreak (Hoogland et al 2018).…”