As one of the world’s worst invasive species, the wild pig (Sus scrofa) has inflicted hundreds of millions of dollars in economic and ecological damages in Texas alone (GISD 2013). The Lone Star State holds the distinction of possessing over half of the estimated six million wild pigs in North America (Doughty & Turner 2019). Populations continue to expand and costs from their direct damages to agriculture alone reach an estimated $800 million annually in Texas (Doughty & Turner 2019). Hunting, trapping, snaring, the use of trained dogs and aerial operations have all been used to help reduce wild pig populations across the state. The use of toxicants is another potential tool to reduce wild pig damage and prevent populations from growing and spreading. Of course, research is ongoing to answer critical questions regarding efficacy and humaneness as well as any potential environmental impacts prior to the use of toxicants, like sodium nitrite, on wild pigs in Texas.
Currently, there are no toxicants that are legally registered for use on wild pigs in Texas. Several toxicants have made it into the news stream recently, but they have not been labeled for public use due to ongoing research, including their potential for secondary toxicity to non-target animals as well as humaneness concerns. Sodium fluoroacetate (Compound 1080), while currently in use for wild pig abatement efforts in countries such as Australia, is a chemical toxicant that has a high persistence in the environment and was traditionally used in coyote eradication efforts prior to its ban from the U.S. in 1972 (Science News 1981). Yellow phosphorus was initially introduced to control rodent populations, but due to the larger amounts necessary for efficacy in larger animals, it is currently impractical for feral swine (O’Brien & Lukins 1990). The effective anticoagulant warfarin has been met with speculation because it may take a few days to a week or more to cause mortality. Opposition and threats of lawsuits against one toxicant manufacturer resulted in the withdrawal of its registration request for application on wild pigs in Texas (Doughty & Turner 2019).
The Captive Feral Swine Research and Demonstration Facility at the Kerr Wildlife Management Area has been testing a promising wild pig control agent – sodium nitrite (NaNO2). A common and relatively inexpensive compound used as a food preservative, sodium nitrite is lethal to wild pigs when ingested at high doses. Death occurs in a relatively short period of time because wild pigs naturally lack an adequate supply of the enzyme methemoglobin reductase, which is required to overturn the effects of nitrite toxicity. The mechanism of mortality of sodium nitrite is hypoxia, whereas the inorganic compound prevents oxygen from being released by red blood cells and utilized by the brain and other vital organs (Campbell et al. 2006). The potential for secondary transfer to non-target species is reduced since most mammals including humans, domestic pets and livestock (except domestic swine) produce sufficient amounts of the enzyme necessary for reduced sensitivity to low doses of sodium nitrite. This chemical degrades quickly in the environment with low rates of bioaccumulation or movement through the food web, and there is also an approved antidote in the compound methylene blue. It is generally accepted as a cost-effective alternative for integrated feral swine damage management in countries such as New Zealand and Australia. Sodium nitrite, which was initially developed in Australia for use on wild pigs, was recently registered by the Australian Pesticides and Veterinary Medicines Authority—Australia's equivalent of the U.S. Environmental Protection Agency, or EPA—in December of 2019. Species-specific bait delivery systems continue to be tested in conjunction with the U.S. Department of Agriculture with the goal of successful application on wild pigs in the U.S. (Doughty & Turner 2019).
Sodium nitrite is still under evaluation by the EPA to review the potential risks to human health. The bait is not labeled for public use yet, but the outlook for pesticide registration remains promising within the next few years. If approved, sodium nitrite should provide private landowners and wildlife managers with another tool in the management toolbox. While best management practices for wild pigs include the thoughtful selection of the best available strategy, many Texas landowners remain eager for additional alternatives to reduce the costly damages inflicted by exotic invasive wild pigs. However, more time is needed to conduct continued field trials in order to ensure a thorough examination of the full range of potential outcomes. Prior to the arrival of any toxicant product to market, educational efforts will be necessary to inform landowners on the proper use and delivery in order to maximize both safety and efficiency. For frequent questions and answers related to sodium nitrite, please view this USDA factsheet.
100 Of the World's Worst Invasive Alien Species. 2013. Global Invasive Species Database (GISD), www.iucngisd.org/gisd/100_worst.php.
Campbell, T.A., S.J. Lapidge, and D.B. Long. 2006. Using baits to deliver pharmaceuticals to feral swine in southern Texas. Wildlife Society Bulletin 34:1184–1189.
Compound 1080 Ban: To Be or Not to Be. 1981. Science News, vol. 120, no. 7, pp. 100–101. JSTOR, www.jstor.org/stable/3966184.
Doughty, R. W., and M.W. Turner. 2019. Feral Hogs: Pork Chops or Sherman Tanks?. Unnatural Texas?: the Invasive Species Dilemma. Texas A&M University Press pp. 63–74.
O’Brien, P. H., and B.S. Lukins. 1990. Comparative dose–response relationships and acceptability of warfarin, brodifacoum and phosphorus to feral pigs. Australian Wildlife Research 17: 101–112.
Written by: Joe Richards, Texas A&M University WFSC ‘22
Edited By: John Kinsey, Wildlife Research Biologist - TPWD