Low Secondary Risks for Captive Coyotes from a Sodium Nitrite Toxic Bait for Invasive Wild Pigs

An acute toxic bait is being developed to deliver micro‐encapsulated sodium nitrite (SN) to stimulate severe methemoglobinemia and humane death for invasive wild pigs (Sus scrofa), thereby providing a new tool for reducing their populations. During April 2016, we evaluated sensitivity to SN and outcomes of secondary consumption in the ubiquitous mammalian scavenger, coyote (Canis latrans), to determine secondary risks of consuming carcasses of wild pigs that died from consuming the SN toxic bait. At the National Wildlife Research Center in Fort Collins, Colorado, USA, we first evaluated whether coyotes fed carcasses of domestic pigs killed by consumption of SN bait showed signs of SN intoxication. Second, we conducted chemical analysis of residual SN in the coyotes for evidence of SN passing from pigs to coyotes. Last, we conducted an acute oral toxicity test (LD50) with SN for coyotes by feeding them meatballs containing capsules of SN. We found no evidence that captive coyotes experienced SN intoxication from consuming on carcasses that had been freshly poisoned with SN, despite consuming ¯ x = 1.6 kg of tissues/coyote within 24 hours. None of the captive coyotes consumed digestive tracts or stomach contents from poisoned carcasses, which contained the highest levels of residual SN. Chemical analysis indicated that only ≤34.14 mg/kg of residual SN were passed from the tissues of the pigs into the coyotes, confirming that SN does not bioaccumulate. All coyotes quickly vomited various doses of SN during the LD50 test and fully recovered, suggesting a natural defense against secondary poisoning from SN. Testing with captive coyotes indicates that the risks of secondary poisoning for free‐ranging coyotes are likely low, although field‐testing should be used to confirm

Exposure of a population of invasive wild pigs to simulated toxic bait containing biomarker: implications for population reduction

BACKGROUND: An international effort to develop an acute and humane toxic bait for invasive wild pigs (Sus scrofa) is underway to curtail their expansion. We evaluated the ability to expose a population of wild pigs to a simulated toxic bait (i.e., placebo bait containing a biomarker, rhodamine B, in lieu of the toxic ingredient) to gain insight on potential population reduction. We used 28 GPS-collars and sampled 428 wild pigs to examine their vibrissae for evidence of consuming the bait. RESULTS: We estimated that 91% of wild pigs within 0.75 km of bait sites (total area = 16.8 km2) consumed the simulated toxic bait, exposing them to possible lethal effects. Bait sites spaced 0.75–1.5 km apart achieved optimal delivery of the bait, but wild pigs ranging ≥ 3 km away were susceptible. Use of wild pig-specific bait stations resulted in no non-target species directly accessing the bait. CONCLUSION: Results demonstrate the potential for exposing a large proportion of wild pigs to a toxic bait in similar ecosystems. Toxic bait may be an effective tool for reducing wild pig populations especially if used as part of an integrated pest management strategy. Investigation of risks associated with a field-deployment of the toxic bait is needed

Development of a Feral Swine Toxic Bait (Hog-Gone®) and Bait Hopper (Hog-Hopper™) in Australia and the USA

At the 13th Wildlife Damage Management Conference, the primary author delivered a paper titled “Is America ready for a humane feral pig ‘toxin’?” The toxin, sodium nitrite, a common meat preservative that prevents botulism, had previously been shown to be a quick-acting and low-residue toxicant for feral pigs in Australia and has since been patented. Pigs are particularly sensitive to nitrite-induced methemoglobinemia because they have low levels of methemoglobin reductase, the enzyme required to reverse the effects of nitrite toxicosis. Over the last two years, a great deal of progress has been made towards developing a nitrite bait and a suitable bait delivery vehicle for feral pigs. Field trials of Hog-Gone® in Australia are now complete and a registration dossier is currently being finalized. The dossier details the pharmacology and humaneness of nitrite toxicosis, pen and field trial efficacy, pen and field carcass residues, and the nontarget safety and environmental fate of nitrite. Nontoxic trials of smaller bite-sized Hog-Gone baits, delivered in the Hog-Hopper™, are currently occurring in multiple sites and seasons in Alabama, Florida, Mississippi, Missouri, Oklahoma, and Texas. Results thus far are encouraging, and may lead to future trials if environmental safety is demonstrated. Concurrently, an Environmental Protection Agency registration dossier is being prepared to request the experimental-use permit needed for field trials of the formulated bait. Engagement with industry and animal welfare groups also continues to be positive. Detailed within, in brief, are the achievements of the last two years and the future of the project in Australia and the USA

Efficacy and risks from a modified sodium nitrite toxic bait for wild pigs

BACKGROUND: Wild pigs (Sus scrofa) are a destructive invasive species throughout many regions of the world. In 2018, a field evaluation of an early prototype of a sodium nitrite (SN) toxic bait in the United States revealed wild pigs dropped large amounts of the toxic bait outside the pig-specific bait stations while feeding, and thus subsequent hazards for non-target animals. We modified the SN-toxic bait formulation, the design of the bait station, and the baiting strategy to reduce dropped bait. We tested the modifications in Queensland, Australia (December 2018), Alabama, USA (August 2019), and Texas, USA (March 2020) under differing climatic and seasonal conditions for one night. RESULTS: Cumulatively we found 161 carcasses of all age classes of wild pigs using systematic transects. Remote camera indices indicated high lethality for wild pigs, achieving population reductions of 76.3 to 90.4%. Wild pigs dropped only small particles of SN-toxic bait (average = 55.5 g per bait site), which represented a 19-fold decrease from the previous trial. Despite this reduction, we found three Australian ravens (Corvus coronoides) in Queensland, two Virginia opossums (Didelphis virginiana) in Alabama, and 35 granivorous-passerine birds (mostly dark-eyed juncos [Junco hyemalis]) in Texas dead from consuming the dropped bait. We did not detect any population-level effects for those species. CONCLUSION: Our modifications were effective at reducing populations of wild pigs, but the deaths of non-target species require further steps to minimize these hazards. Next steps will include evaluating various deterrent devices for birds the morning after SN-toxic bait has been offered

Preliminary Assessment of the HogHopper™ for Excluding Non-Target Wildlife

Feral swine populations are expanding throughout the U.S., where they are causing increasing amounts of damage to agriculture, natural resources, and property and threaten human health and safety. Methods to control feral swine damage in the U.S. consist of integrated fencing, trapping, snaring, and shooting (including hunting with dogs) efforts. New methods that are being developed to control feral swine damage include toxicants and fertility control agents. For these emerging technologies to be effective at the population level, they must function through oral routes of delivery. Concurrent to the development of orallydelivered actives, a cost-effective system that delivers biologics to feral swine while restricting access to non-target wildlife, needs to be developed. Our objectives are to 1) describe historical efforts to develop a feral swine-specific oral delivery system in the U.S., 2) present preliminary findings from an ongoing collaborative evaluation of the Australian-made HogHopper™, and 3) outline future opportunities in developing a feral swine-specific oral delivery system. While there is a real need for a feral swine-specific oral delivery system, presently there is no universally effective system suitable for all applications and field scenarios. Each system has its advantages and disadvantages that must be assessed within its management context

Low Secondary Risks for Captive Coyotes from a Sodium Nitrite Toxic Bait for Invasive Wild Pigs

An acute toxic bait is being developed to deliver micro‐encapsulated sodium nitrite (SN) to stimulate severe methemoglobinemia and humane death for invasive wild pigs (Sus scrofa), thereby providing a new tool for reducing their populations. During April 2016, we evaluated sensitivity to SN and outcomes of secondary consumption in the ubiquitous mammalian scavenger, coyote (Canis latrans), to determine secondary risks of consuming carcasses of wild pigs that died from consuming the SN toxic bait. At the National Wildlife Research Center in Fort Collins, Colorado, USA, we first evaluated whether coyotes fed carcasses of domestic pigs killed by consumption of SN bait showed signs of SN intoxication. Second, we conducted chemical analysis of residual SN in the coyotes for evidence of SN passing from pigs to coyotes. Last, we conducted an acute oral toxicity test (LD50) with SN for coyotes by feeding them meatballs containing capsules of SN. We found no evidence that captive coyotes experienced SN intoxication from consuming on carcasses that had been freshly poisoned with SN, despite consuming ¯ x = 1.6 kg of tissues/coyote within 24 hours. None of the captive coyotes consumed digestive tracts or stomach contents from poisoned carcasses, which contained the highest levels of residual SN. Chemical analysis indicated that only ≤34.14 mg/kg of residual SN were passed from the tissues of the pigs into the coyotes, confirming that SN does not bioaccumulate. All coyotes quickly vomited various doses of SN during the LD50 test and fully recovered, suggesting a natural defense against secondary poisoning from SN. Testing with captive coyotes indicates that the risks of secondary poisoning for free‐ranging coyotes are likely low, although field‐testing should be used to confirm

Development of Toxic Bait to Control Invasive Wild Pigs and Reduce Damage

Populations of invasive wild pigs (Sus scrofa) are increasing in many regions of the world, in particular the United States and Australia. Invasive wild pigs cause extensive damage to ecological resources and agriculture. Development and registration of a safe and humane toxic bait offers a practical and cost effective tool to control invasive species. Currently, no toxicants are approved for use on invasive wild pigs in the United States and those approved in Australia are under scrutiny because of concerns regarding humaneness and effects on nontarget species. We tested a newly formulated bait containing the microencapsulated active ingredient, sodium nitrite (HOGGONE®; Animal Control Technologies Australia P/L, Victoria, Australia), that is considered humane and safer for nontarget species because it does not bioaccumulate. We examined palatability, lethality, and stability of the bait (i.e., fresh compared to 8-monthold bait) on groups of captive invasive wild pigs. We found HOGGONE® was a preferred food item, averaging 475 g of toxic bait consumed per animal during the first night offered. Consumption of HOGGONE® resulted in 95% mortality (53 of 56) in the treatment groups across 2 treatment nights. Most mortalities (98%) occurred during the first night the toxic bait was offered. Camera evidence suggested that deaths occurred within 3 hr post-offering. The toxic bait was stable and effective up to 8 months post manufacture. Our results support current applications to register HOGGONE® for reducing damage from invasive wild pigs in the United States and Australia. Further research is required to evaluate HOGGONE® on free-ranging invasive wild pigs using bait stations that exclude nontarget species

Effectiveness and target-specificity of a novel design of food dispenser to deliver a toxin to feral swine in the United States

There are no registered toxins available for use on Feral Swine (Sus scrofa, Linnaeus) in the United States. HOGGONE is a proprietary bait matrix under development in Australia that delivers toxic levels of sodium nitrite to feral swine. However, one challenge is to develop a species-specific oral delivery system to deliver toxins to feral swine in the USA while minimizing non-target wildlife exposure. The HOGHOPPERTM is a lightweight and portable bait delivery system that could overcome this problem. Our objective was to compare non-toxic HOGGONE removal by wildlife that visited HOGHOPPERS during acclimation periods (doors open; free-feeding stage) and activation periods (doors closed; simulated toxic stage) at sites throughout the United States. We conducted 38 HOGHOPPER trials on private and public land in Alabama, Florida, Oklahoma, and Texas, and determined species-specific visitation and HOGGONE removal rates using motion-sensing digital camera systems. We found activated HOGHOPPERS to successfully exclude all wildlife except feral swine and Raccoon (Procyon lotor, Linnaeus). For raccoons the number of baits removed per 24h was reduced by 92% during the HOGHOPPER activation period. No other wildlife removed HOGGONE from HOGHOPPERS. During trials in which raccoon breaches occurred, an extended acclimation period was used. To minimize raccoon exposure risks, an abbreviated acclimation period o