We evaluated the effects of fipronil bait pellets on two cricetids that commonly occupy colonies of black-tailed prairie dogs (Cynomys ludovicianus; BTPDs): western deer mice (Peromyscus sonoriensis) and northern grasshopper mice (Onychomys leucogaster). In one experiment, bait pellets (0.96 mg fipronil/bait) were applied at 75 baits/ha to three 1.44-ha plots on a BTPD colony. Mouse abundance declined by 70% from before to 6-10 d after treatment. In a second experiment, bait pellets (0.46 or 1.52 mg fipronil/bait) were applied at 125 baits/ha to four plots (0.85-1.86 ha) on two BTPD colonies; two non-treated plots were baselines (1.09 and 2.06 ha). From before to 11-15 d after treatment, mouse abundance declined by 51%- 67% on the treated plots vs. a decline of 9% on the non-treated plots. Mouse survival from before to 11-15 d after treatment was 51% lower on the treated plots. In a third experiment, bait pellets (0.84 mg fipronil/bait) were applied at 125 baits/acre on two 1.44-ha plots on a BTPD colony; two 1.44-ha non-treated plots were baselines. Mouse survival from before to 30-44 d after treatment was 45% lower on the treated plots; the abundance of deer mice on the treated plots remained similar from before to 30-44 d after treatment, perhaps due to juvenile recruitment and/or immigration. In a laboratory experiment, 33 deer mice offered one bait pellet (0.86 mg fipronil/bait) consumed 27% of their bait, on average (range = 0-100%). Over 3 d, deer mouse mortality was estimated at 53%; mortality increased with fipronil dose, which averaged 11 mg fipronil/kg body mass (range = 3-46 mg/kg). Brain samples were available from 31 deer mice; all tested positive for fipronil sulfone, the primary mammalian metabolite of fipronil, at 19 to 61,205 ng fipronil sulfone/g. Additional experiments could determine if these findings scale up to larger landscapes.

Plague is a zoonotic disease of mammalian hosts and flea vectors. Wildlife biologists most commonly mitigate plague by controlling flea populations. We evaluated the efficacy of edible baits for systemic flea control with two cricetid species on colonies of black-tailed prairie dogs (Cynomys ludovicianus): the western deer mouse (Peromyscus sonoriensis) and the northern grasshopper mouse (Onychomys leucogaster). We tested grain bait with 0.005% fipronil by weight and "FipBit" pellets with 0.46-1.52 mg of fipronil/pellet. Flea prevalence was assessed via combing of live-trapped mice. In one experiment with fipronil grain bait and FipBits (n=564 combings), flea prevalence declined from 74% (grain) and 45% (FipBits) before treatments to 0% for both treatments from 30-44 d and from 324-413 d after treatments. During a second experiment with FipBits (n=299 combings), flea prevalence declined from 13% to 32% before treatments to 0% from 11-15 d after treatments, but increased to 29-56% from 349-378 d after treatments. Results herein suggest annual fipronil bait treatments may be most effective for flea control.

The flea-borne agent of plague, Yersinia pestis, is lethal to endangered black-footed ferrets (Mustela nigripes, BFFs) and the prairie dogs (Cynomys spp., 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 (C. ludovicianus, BTPDs), Gunnison's PDs (C. gunnisoni, GPDs), and Richardson's ground squirrels (Urocitellus richardsonii, 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.

Plague is a zoonotic disease of mammals caused by the bacterium Yersinia pestis. Because plague is primarily transmitted by fleas (Siphonaptera), rates of plague transmission are expected to increase with flea abundance. Edaphic factors can influence the abundance and dispersion of fleas, suggesting that soils may play important roles in plague ecology. From June to August 2010-12, in northern New Mexico, USA, we investigated the effects of soil texture, soil moisture, and soil water-holding capacity on the abundance of adult fleas parasitizing colonial, burrowing black-tailed prairie dogs (Cynomys ludovicianus, BTPDs). We sampled BTPDs 1,741 times on 20 sampling plots distributed among 13 BTPD colonies, detecting 9,541 adult fleas on BTPDs. Fleas were most abundant on BTPDs in areas with coarse surface soils, and in areas with moderately textured subsurface soils at the average depth of BTPD nest chambers. Coarse surface soils may facilitate water percolation to BTPD nests, where the moisture could generate humid microclimates that benefit desiccation-prone fleas. Moderately textured subsurface soils, of intermediate water-holding capacity, can store water, which may increase burrow humidity. Moreover, moderately textured subsurface soils in BTPD nests may increase survival of flea larvae and pupae, facilitating their development to adulthood. That said, excessive moisture and sodden soils can favor fungi and mites, some of which are lethal to fleas. In our study, fleas were most abundant in areas with subsurface soils of intermediate moisture content. Our findings complement an accumulating number of studies, indicating that edaphic factors play important roles in flea and plague ecology.

Intraspecific resource partitioning may play a critical role in how predators optimize prey selection. The Black-footed Ferret (Mustela nigripes; henceforth, ferret) is a highly specialized predator of prairie dogs (Cynomys spp.; henceforth, PDs). Adult ferrets are sexually dimorphic and PDs are of similar size making them a difficult prey item. PD young are born 6 to 8 weeks prior to births of ferrets, producing a crop of smaller prey items during a period when energetic needs of female ferrets are highest. We asked whether relatively small female ferrets select small PDs as prey. We examined survival rates from early to late summer for large and small black-tailed PDs (Cynomys ludovicianus) in Montana and South Dakota as a function of their distance to adult male and female ferrets using capture-mark-recapture of PDs and simultaneous summer monitoring of ferret locations. Survival of small PDs (<600 g) was low when a female ferret was nearby, but distance to nearest female ferret did not affect survival of large PDs. Distance to the nearest male ferret did not influence survival regardless of PD size. Reduced competition from males for a critical food resource needed by females rearing young would benefit fitness of both sexes. If female ferrets depend on young PDs during their reproductive period, existing habitat models may substantially overestimate ferret carrying capacity.

The consequences of intraguild predation on vulnerable subordinate species are an important consideration in the recovery of endangered species. In prairie ecosystems, coyotes (Canis latrans) are the primary predator of endangered black-footed ferrets (Mustela nigripes; hereafter, ferrets) and presumably compete for prairie dog (Cynomys spp.) prey. Coyote predation of ferrets is thought to occur at night when ferrets are active aboveground; however, the apparent source of competition, diurnal prairie dogs, are belowground and inaccessible to coyotes at this time, presenting a perplexing temporal mismatch between actual and expected times that coyotes and ferrets come into conflict. Our study used remote wildlife cameras, occupancy models, and overlap of circadian activity patterns to investigate how landscape features, prairie dog colony attributes, and attraction to sympatric species, i.e., American badgers (Taxidea taxus; hereafter, badgers) and lagomorphs (cottontail rabbits and jackrabbits) influence Coyote use of prairie dog colonies and potential Coyote-ferret interactions. We first evaluated Coyote use (i.e., occupancy) between prairie dog colonies and surrounding available grasslands, finding that coyotes whose home ranges include prairie dog colonies used colonies nearly twice as much as surrounding grasslands. Next, we investigated biotic and abiotic factors that may influence Coyote use and frequency of use (i.e., detection probability) on prairie dog colonies. We found high Coyote use across all areas on prairie dog colonies; however, their frequency of use increased in areas that were also used by badgers. High overlap between Coyote and badger activity patterns (81%) further supports the spatial use patterns revealed by our occupancy analysis, and badgers and coyotes are known to form hunting associations. Interspecific competition and overlapping patterns of resource use between badgers and ferrets have been documented in previous studies; our study supports these findings and suggests that Coyote attraction to badger activity may influence Coyote-ferret interactions. Coyotes are the primary predator of endangered black-footed ferrets, a species that selects similar resources and competes with American badgers for prairie dog prey. Our study found that coyotes use prairie dog colonies preferentially to surrounding grasslands, and on colonies, coyotes use areas more frequently that are also used by American badgers. This suggests that Coyote attraction to American Badger activity may influence where and how coyotes and black-footed ferrets interact. Las consecuencias de la depredaci & oacute;n intragremial sobre especies subordinadas vulnerables son una consideraci & oacute;n importante en la recuperaci & oacute;n de especies en peligro de extinci & oacute;n. En ecosistemas de pradera, los coyotes (Canis latrans) son el depredador primario de los hurones de pies negros (Mustela nigripes; en adelante, hurones) en peligro de extinci & oacute;n y presumiblemente compiten por las presas de los perritos de las praderas (Cynomys spp.). Se cree que la depredaci & oacute;n de hurones por parte de los coyotes ocurre durante la noche, cuando los hurones est & aacute;n activos en la superficie; sin embargo, la fuente aparente de competencia, los perritos de las praderas diurnos, est & aacute;n bajo tierra y son inaccesibles para los coyotes en este momento, lo que presenta un desconcertante desajuste temporal entre los momentos reales y esperados en que los coyotes y los hurones entran en conflicto. Nuestro estudio utiliz & oacute; c & aacute;maras trampa, modelos de ocupaci & oacute;n y superposici & oacute;n de patrones de actividad circadiana para investigar c & oacute;mo las caracter & iacute;sticas del paisaje, los atributos de las colonias de perritos de las praderas y la atracci & oacute;n por especies simp & aacute;tricas (es decir, tejones americanos, Taxidae taxus y lagomorfos) influyen en el uso de las colonias de los perritos de las praderas por parte de los coyotes e interacciones potenciales entre coyote-hur & oacute;n. Primero evaluamos el uso de coyotes (es decir, ocupaci & oacute;n) entre las colonias de perritos de las praderas y los pastizales circundantes disponibles, y encontramos que los coyotes cuyo territorio colinda con colonias de perritos de la pradera usaban las colonias casi el doble (Psi<^> = 0,77, IC del 95% [0,48, 0,93]) que los pastizales circundantes (Psi<^> = 0,37; IC del 95% [0,21; 0,57]). Despu & eacute;s investigamos los factores bi & oacute;ticos y abi & oacute;ticos que pueden influir en el uso y la frecuencia de uso de los coyotes (es decir, la probabilidad de detecci & oacute;n) en las colonias de perritos de las praderas. Encontramos un alto uso por parte de los coyotes en todas las & aacute;reas de las colonias de perritos de las praderas; sin embargo, su frecuencia de uso aument & oacute; en & aacute;reas que tambi & eacute;n eran utilizadas por tejones (beta = 3,95, IC del 95% [2,35, 5,58]). La alta superposici & oacute;n entre los patrones de actividad de coyotes y tejones (81%) respalda a & uacute;n m & aacute;s los patrones de uso espacial revelados por nuestro an & aacute;lisis de ocupaci & oacute;n, y se sabe que los tejones y los coyotes forman asociaciones de caza. En estudios previos se han documentado la competencia interespec & iacute;fica y los patrones superpuestos de uso de recursos entre tejones y hurones; nuestro estudio respalda estos hallazgos y sugiere que la atracci & oacute;n del coyote por la actividad del tej & oacute;n puede influir en las interacciones coyote-hur & oacute;n.

Sylvatic plague, caused by the flea-borne bacterium Yersinia pestis, is an invasive disease in North America that causes reductions of native fauna and transforms ecosystems. Fipronil baits have shown promise in reducing flea loads on prairie dogs Cynomys spp. for plague mitigation. Many species depend on prairie dogs and their ecological influences, including the black-footed ferret Mustela nigripes (ferret), an obligate predator of prairie dogs. To better understand how fipronil affects ferrets, we offered carcass portions from black-tailed prairie dogs C. ludovicianus that had consumed fipronil bait (0.005% fipronil by weight) to captive ferrets and monitored their health. We fed carcass portions of three prairie dogs to four adult ferrets for 1 week. No ill effects were observed in the ferrets. We collected scat from the ferrets before, during, and after their feeding on treated prairie dogs. We evaluated potential effects of ferret scat on larval fleas, which feed on organic matter. Fipronil residues were not detected in ferret scat samples collected before treatment. During and shortly after treatment, ferret scat contained 3.76 ng/g fipronil and 13.75 ng/g fipronil sulfone, on average, demonstrating trophic transfer of the residues from prey to predator. We presented 0.5 mg of ferret scat to each of 96 larval Oropsylla montana (Siphonaptera: Ceratophyllidae) and assessed survival rates over 24 h. When exposed to ferret scat lacking fipronil residues, 85% of larvae survived. Survival was reduced to 61% and 35% for larvae contacting or consuming scat with fipronil residue, respectively. Fipronil residues in scat from a variety of species on prairie dog colonies, perhaps especially the prairie dogs, may assist in flea control and plague mitigation. Hosts eliminate fipronil residues, and fipronil residues in the environment degrade over time, reducing but not eliminating potential concerns with bioaccumulation.

Sylvatic plague, a primarily flea-borne zoonosis, is a significant threat to prairie dogs (Cynomys spp., PDs) and their specialized predators, endangered black-footed ferrets (Mustela nigripes, BFFs). Host-fed fipronil baits have proven effective in controlling fleas on PDs for the purposes of plague mitigation and BFF conservation. Currently, annual treatments are the norm. We tested the long-term efficacy of fipronil bait treatments with black-tailed PDs (C. ludovicianus, BTPDs) and BFFs in South Dakota, USA. During 2018-2020, we provided BTPDs on 21 sites with grain bait formula, laced with 0.005% fipronil (50 mg/kg); 18 non-treated sites functioned as baselines. In 2020-2022, we live-trapped, anesthetized, and combed BTPDs for fleas. Flea control was significant for at least 639-885 days. Flea abundance on the treated sites was < 0.5 fleas/BTPD for -750 days. During 2020-2022, we sampled BFFs for fleas on 4 BTPD colonies treated with fipronil grain bait and 8 non-treated colonies. Flea control was significant with BFFs, but flea abundance began to rebound within -240 days post-treatment. When feasible, the combination of insecticide treatments, such as fipronil baits, and BFF vaccination against plague provide a "two-pronged" protection approach for these endangered carnivores. If fipronil bait treatments are less effective with predatory BFFs than PDs, as found herein, the "two-pronged" approach might be used to protect BFFs and biennial fipronil bait treatments might be used to protect PDs. If BFF vaccination is not possible, or few BFFs can be vaccinated, annual fipronil bait treatments might be used as a precaution to protect BFFs. Flea densities might be surveyed to determine when/where more frequent treatments seem useful.

Plague, caused by the bacterium Yersinia pestis, is a zoonotic disease of mammalian hosts and flea vectors. Fipronil baits have been used to suppress adult fleas for plague mitigation. The degree and duration of flea control may increase if fipronil also kills other stages in the flea life cycle. We fed grain treated with 0.005% fipronil by weight, or nontreated grain, to black-tailed prairie dogs (Cynomys ludovicianus), which excrete fipronil and metabolites in their feces after consuming fipronil in their diet. We presented prairie dog feces to 331 larval Oropsylla montana (Siphonaptera: Ceratophyllidae). When exposed to feces lacking fipronil or metabolites, 84% of larvae survived for 24 h. In contrast, survival declined to 42% for larvae contacting feces from fipronil-treated prairie dogs. Just 7% of larvae consuming feces from fipronil-treated prairie dogs survived. Fipronil and metabolites may persist in host feces for several months or longer in prairie dog burrows where flea larvae dwell and forage. The lethal effects of fipronil on adult and larval fleas (and perhaps other life stages) may help to explain why fipronil baits are capable of suppressing fleas on prairie dogs for ≥12 mo.

Sylvatic plague is a widespread, primarily flea-vectored disease in western North America. Because plague is highly lethal to endangered black-footed ferrets (Mustela nigripes, BFFs) and the prairie dogs (Cynomys spp., PDs) on which BFFs depend for habitat and prey, minimizing the impacts of plague is a priority at BFF reintroduction sites. We developed a new, flour-based bait pellet containing 0.84 mg of fipronil and weighing ∼1.25 g (FipBits). We measured the degree and duration of flea control on black-tailed PDs (C. ludovicianus) in Montana and on Gunnison's PDs (C. gunnisoni) in Arizona, USA from 2018-2020. FipBits were distributed on treated plots one time at a rate of 125/ha. Fleas were virtually eliminated in Montana from 1 mo posttreatment to 1 yr later and remained substantially depressed 2 yr posttreatment. With the split colony design, we probably underestimated the degree of flea control achieved with FipBits due to crossover edge effects along the arbitrary line dividing the plots. Flea control in Arizona was significant from 1 mo posttreatment to 1 yr later, but flea abundance had recovered by 2 yr posttreatment. Flea control was evaluated from 2020-2021 in South Dakota, USA on four plots treated with three concentrations of fipronil in FipBits (0.68, 0.71, and 0.83 mg/FipBit). Fleas were essentially eliminated for 10 mo on the 0.83-mg plot and were substantially reduced on the two 0.71-mg plots. Fleas were reduced on the 0.68-mg plot, but the degree of control was less than observed on other treated plots. Impacts of plague on PDs and BFFs would probably be greatly reduced by the levels of flea control observed with FipBits. Options for expanded FipBit evaluations are being pursued for what may become a highly practical, affordable, and effective plague mitigation tool.

Parasite infrapopulation size -the population of parasites affecting a single host -is a central metric in parasi-tology. However, parasites are small and elusive such that imperfect detection is expected. Repeated sampling of parasites during primary sampling occasions (e.g., each host capture) informs the detection process. Here, we estimate flea (Siphonaptera) infrapopulation size on black-tailed prairie dogs (Cynomys ludovicianus, BTPDs) as a proof-of-concept for estimating parasite infrapopulations given imperfect detection. From Jun-Aug 2011, we live-trapped 299 BTPDs for a total of 573 captures on 20 plots distributed among 13 colonies at the Vermejo Park Ranch, New Mexico, USA. During each capture, an anesthetized BTPD was combed 3 times consecutively, 15 s each, to remove and count fleas. Each flea (n = 4846) was linked to the BTPD from which it was collected and assigned an encounter history ('100', '010', '001'). We analyzed the encounter histories using Huggins closed captures models, setting recapture probabilities to 0, thereby accounting for flea removal from hosts. The probability of detecting an individual flea (p) increased with Julian date; field personnel may have become more efficient at combing fleas as the field season progressed. Combined p across 3 combings equaled 0.99. Estimates of flea infrapopulation size were reasonable and followed the negative binomial distribution. Our general approach may be broadly applicable to estimating infrapopulation sizes for parasites. The utility of this approach increases asp declines but, if p is very low, inference is likely limited.

We evaluated the invasion of plague bacteria Yersinia pestis into a population of black-tailed prairie dogs (Cynomys ludovicianus; BTPDs) in South Dakota. We aimed to ascertain if Y. pestis invaded slowly or rapidly, and to determine if vector (flea) control or vaccination of BTPDs assisted in increasing survival rates. We sampled BTPDs in 2007 (before Y. pestis documentation), 2008 (year of confirmed invasion), and 2009 (after invasion). We estimated annual BTPD re-encounter rates on three 9-ha plots treated annually with deltamethrin dust for flea control and three 9-ha plots lacking dust. In 2007 and 2008, approximately half the adult BTPDs live-trapped were injected subcutaneously with either an experimental plague vaccine (F1-V fusion protein) or placebo formulation; the remaining individuals were not inoculated. From 2007 to 2009, we sampled 1559 BTPDs on 2542 occasions. During 2007-2008, the prevalence and intensity of fleas on BTPDs were 69-97% lower on the dusted vs. no dust plots. From 2007 to 2008, the annual re-encounter rate of non-inoculated BTPDs was 150% higher on the dusted vs. no dust plots. During the same interval on the dusted plots, the re-encounter rate was 55% higher for vaccinated adult female BTPDs vs. nonvaccinated adult females, but the annual re-encounter rate was 19% lower for vaccinated adult males. By late August 2008, BTPDs were nearly extirpated from the no dust plots. During 2007-2008 and 2008-2009 on the dusted plots, which persisted, the BTPD re-encounter rate was 41% higher for vaccinated vs. non-vaccinated adult females but 35% lower for vaccinated adult males. Yersinia pestis erupted with vigor as it invaded. Flea control enhanced BTPD survival but did not offer full protection. Flea control and F1-V vaccination seemed to have additive, positive effects on adult females. Annual re-encounter rates were reduced for vaccinated adult males; additional experimentation is needed to further evaluate this trend.

Several explanations have been posited for how the plague bacterium (Yersinia pestis) reemerges during sylvatic cycles within the same foci over many years, and often without direct evidence of host die-offs. One prevalent view is that transmission-optimized Y. pestis bacteria, exhibiting epizootic/enzootic behavior, almost continually replicate and survive through repeated, linked, host-centered propagation events. These bacteria, we will refer to as "r-pestis" type ecotype(s), represent a limited number of phenotypic lineages exhibiting optimal transmissibility and high rates of reproduction. These attributes, it is thought, assure their durability through time. For continuous r-pestis type expansions to be successful, adequate numbers of fleas and hosts must become infected to produce massive numbers of bacteria. In the process, host and flea numbers decline as they succumb to plague. Here we hypothesize that r-pestis population expansions seed the environment and confront a unique, highly competitive local milieu, where natural selection favors new ecotypes that incorporate a range of emergent adaptive survival strategies. These newly adapted survivors we recognize as a range of "K-pestis" ecotypes with greater durability and lower reproduction rates. These emergent K-pestis forms may arise in succession or coexist for varying periods of time with r-pestis ecotypes, and with other K-pestis ecotypes. Among K-pestis ecotypes, we hypothesize that through adaptive radiations, some persist within flea life stages, soil, organic waste, amoebae, plants, carcasses, hosts, or within niches yet to be characterized. In some settings, after a long quiet period, when favorable, K-pestis bacteria may trigger a singular event where an r-pestis transmission stream emerges precipitating another enzootic/epizootic progression. If this hypothesis withstands rigorous testing, then Y. pestis might represent an even more formidable, enduring, and adaptable foe, where unforeseen local events could trigger new epidemic and epizootic/enzootic events threatening humans and populations of other mammals, including those of conservation concern.

Background Plague, a widely distributed zoonotic disease of mammalian hosts and flea vectors, poses a significant risk to ecosystems throughout much of Earth. Conservation biologists use insecticides for flea control and plague mitigation. Here, we evaluate the use of an insecticide grain bait, laced with 0.005% fipronil (FIP) by weight, with black-tailed prairie dogs (BTPDs, Cynomys ludovicianus). We consider safety measures, flea control, BTPD body condition, BTPD survival, efficacy of plague mitigation, and the speed of FIP grain application vs. infusing BTPD burrows with insecticide dusts. We also explore conservation implications for endangered black-footed ferrets (Mustela nigripes), which are specialized predators of Cynomys. Principal findings During 5- and 10-day laboratory trials in Colorado, USA, 2016-2017, FIP grain had no detectable acute toxic effect on 20 BTPDs that readily consumed the grain. During field experiments in South Dakota, USA, 2016-2020, FIP grain suppressed fleas on BTPDs for at least 12 months and up to 24 months in many cases; short-term flea control on a few sites was poor for unknown reasons. In an area of South Dakota where plague circulation appeared low or absent, FIP grain had no detectable effect, positive or negative, on BTPD survival. Experimental results suggest FIP grain may have improved BTPD body condition (mass:foot) and reproduction (juveniles:adults). During a 2019 plague epizootic in Colorado, BTPDs on 238 ha habitat were protected by FIP grain, whereas BTPDs were nearly eliminated on non-treated habitat. Applications of FIP grain were 2-4 times faster than dusting BTPD burrows. Significance Deltamethrin dust is the most commonly used insecticide for plague mitigation on Cynomys colonies. Fleas on BTPD colonies exhibit the ability to evolve resistance to deltamethrin after repeated annual treatments. Thus, more tools are needed. Accumulating data show orally-delivered FIP is safe and usually effective for flea control with BTPDs, though potential acute toxic effects cannot be ruled out. With continued study and refinement, FIP might be used in rotation with, or even replace deltamethrin, and serve an important role in Cynomys and black-footed ferret conservation. More broadly, our stepwise approach to research on FIP may function as a template or guide for evaluations of insecticides in the context of wildlife conservation.

All pathogenic organisms are exposed to abiotic influences such as the microclimates and chemical constituents of their environments. Even those pathogens that exist primarily within their hosts or vectors can be influenced directly or indirectly. Yersinia pestis, the flea-borne bacterium causing plague, is influenced by climate and its survival in soil suggests a potentially strong influence of soil chemistry. We summarize a series of controlled studies conducted over four decades in Russia by Dr. Evgeny Rotshild and his colleagues that investigated correlations between trace metals in soils, plants, and insects, and the detection of plague in free-ranging small mammals. Trace metal concentrations in plots where plague was detected were up to 20-fold higher or lower compared to associated control plots, and these differences were >2-fold in 22 of 38 comparisons. The results were statistically supported in eight studies involving seven host species in three families and two orders of small mammals. Plague tended to be positively associated with manganese and cobalt, and the plague association was negative for copper, zinc, and molybdenum. In additional studies, these investigators detected similar connections between pasturellosis and concentrations of some chemical elements. A One Health narrative should recognize that the chemistry of soil and water may facilitate or impede epidemics in humans and epizootics in non-human animals.

Wildlife diseases are a major concern for species survival around the world. Vector-borne diseases, in particular, are problematic for both humans and wildlife. Plague is an introduced disease to North America where many species have low natural resistance to infection by the causative bacterium, Yersinia pestis. Plague in the United States is often associated with large-scale epizootic events that impact rodent populations. However, we need more information regarding the effects of plague at enzootic levels and in species that rarely if ever experience epizootic events. New Mexico is a state that experiences regular epizootic plague events in several species of rodents but comparatively less is known about enzootic plague impacts within rodent communities in New Mexico. The Peñasco least chipmunk (Neotamias minimus atristriatus) is state-listed as endangered in New Mexico and is a candidate for listing under the federal Endangered Species Act. It likely has been extirpated from the southern portion of its range and is now observed only at high elevations in isolated areas in the White Mountains. We evaluated plague presence in the more abundant small mammal species associated with these chipmunks. We used an F1 antigen plague-specific vaccine and a placebo injection to test whether plague was present and reducing survival in western deer mouse (Peromyscus sonoriensis) and vole (Microtus spp.) populations in the Lincoln National Forest. The effect of plague on survival differed among years and sites. Monthly apparent survival was up to 60 % higher for rodents given the vaccine compared to those given a placebo. Our results suggest that plague is likely impacting the small mammal community in the Lincoln National Forest and is even present at higher elevation sites where the Peñasco least chipmunk was most recently extirpated. Because least chipmunks are highly susceptible to plague, our results suggest that this disease may be an important factor in the population decline of the Peñasco least chipmunk.

Context Vector-borne diseases have caused global pandemics and were responsible for more human deaths than all other causes combined in prior centuries. In the past 60 years, prevention and control programs have helped reduce human mortality from vector-borne diseases, but impacts of those control programs on wildlife populations are not well documented. Insecticides are used to reduce vector-borne diseases in several critically endangered animal populations. Although insecticides are often effective at controlling targeted vectors, their effects on non-target species have rarely been examined. Aims To evaluate the impact of deltamethrin (an insecticide) on sympatric non-target species in areas affected by sylvatic plague, a lethal flea-borne zoonosis. Methods We compared flea control and the effect of deltamethrin application on survival of non-target small mammals (Peromyscus maniculatus, Chaetodipus hispidus, Microtus spp., and Reithrodontomys megalotis) at three study locations in South Dakota, Colorado, and Idaho, USA. Key results Deltamethrin treatments were more effective in reducing fleas on P. maniculatus and Microtus spp. than C. hispidus. Following burrow, nest, and bait-station applications of deltamethrin dust, apparent small mammal survival was greater for non-treatment animals than for flea-reduction animals. However, the magnitude of the difference between treated and non-treated animals differed among host species, study location, time interval, and treatment application method. Conclusions Our results suggest that considering the impact of deltamethrin on co-occurring non-target species before widespread application in future insecticide applications is warranted. Implications Insecticide application methods warrant consideration when designing plague management actions.

Purpose of Review:In 2020, the Appropriations Committee for the U.S. House of Representatives directed the CDC to develop a national One Health framework to combat zoonotic diseases, including sylvatic plague, which is caused by the flea-borne bacterium Yersinia pestis. This review builds upon that multisectoral objective. We aim to increase awareness of Y. pestis and to highlight examples of plague mitigation for One Health purposes (i.e., to achieve optimal health outcomes for people, animals, plants, and their shared environment). We draw primarily upon examples from the USA, but also discuss research from Madagascar and Uganda where relevant, as Y. pestis has emerged as a zoonotic threat in those foci. Recent Findings:Historically, the bulk of plague research has been directed at the disease in humans. This is not surprising, given that Y. pestis is a scourge of human history. Nevertheless, the ecology of Y. pestis is inextricably linked to other mammals and fleas under natural conditions. Accumulating evidence demonstrates Y. pestis is an unrelenting threat to multiple ecosystems, where the bacterium is capable of significantly reducing native species abundance and diversity while altering competitive and trophic relationships, food web connections, and nutrient cycles. In doing so, Y. pestis transforms ecosystems, causing "shifting baselines syndrome" in humans, where there is a gradual shift in the accepted norms for the condition of the natural environment. Eradication of Y. pestis in nature is difficult to impossible, but effective mitigation is achievable; we discuss flea vector control and One Health implications in this context. Summary:There is an acute need to rapidly expand research on Y. pestis, across multiple host and flea species and varied ecosystems of the Western US and abroad, for human and environmental health purposes. The fate of many wildlife species hangs in the balance, and the implications for humans are profound in some regions. Collaborative multisectoral research is needed to define the scope of the problem in each epidemiological context and to identify, refine, and implement appropriate and effective mitigation practices.

Prairie dogs in the western United States experience periodic epizootics of plague, caused by the flea-borne bacterial pathogen Yersinia pestis. An early study indicated that Oropsylla hirsuta (Baker), often the most abundant prairie dog flea vector of plague, seldom transmits Y. pestis by the classic blocked flea mechanism. More recently, an alternative early-phase mode of transmission has been proposed as the driving force behind prairie dog epizootics. In this study, using the same flea infection protocol used previously to evaluate early-phase transmission, we assessed the vector competence of O. hirsuta for both modes of transmission. Proventricular blockage was evident during the first two weeks after infection and transmission during this time was at least as efficient as early-phase transmission 2 d after infection. Thus, both modes of transmission likely contribute to plague epizootics in prairie dogs.

Bubonic plague is a lethal bacterial disease of great historical importance. The plague organism, Yersinia pestis, is primarily transmitted by fleas (Siphonaptera). In natural settings, where its range expands, Y. pestis resides in association with wild rodents and their fleas (sylvatic plague). While chemical insecticides are used against plague vector fleas, biological approaches have not been as critically evaluated. Benign and cost-effective control methods are sorely needed, particularly where imperiled species are at risk. Here we explore the potential of two representative insect pathogenic fungi, Beauveria bassiana Vuillemin 1912 (Hypocreales: Cordycipitaceae) and Metarhizium anisopliae Metschnikoff 1879 (Hypocreales: Clavicipitaceae), each already used commercially worldwide in large-scale agricultural applications, as candidate biopesticides for application against fleas. We review the life cycles, flea virulence, commercial production, and field application of these fungi, and ecological and safety considerations. Pathogenic fungi infections among natural flea populations suggest that conditions within at least some rodent burrows are favorable, and laboratory studies demonstrate lethality of these fungi to at least some representative flea species. Continued study and advancements with these fungi, under appropriate safety measures, may allow for effective biocontrol of plague vector fleas to protect imperiled species, decrease plague outbreaks in key rodent species, and limit plague in humans.