Encapsulated sodium nitrite as a new toxicant for possum control in New Zealand

Sodium nitrite (NaNO₂), a commonly used food preservative, has been researched in New Zealand for the control of brushtail possums (Trichosurus vulpecula). In sufficiently high doses, NaNO₂ is toxic because it disrupts circulatory transport of oxygen. As NaNO₂ is very bitter, encapsulation and mixing it through a highly palatable bait formulation is necessary to effectively deliver it to target pest species. In no-choice cage trials, 12/12 possums consumed a lethal dose of toxic paste bait and died on average after 95.6 minutes (±4.9 SE). In two-choice cage trials 7/8 possums consumed a lethal dose of toxic paste bait and died on average after 96.7 minutes (±11.4 SE). Two field trials targeting possums using this toxic paste in bait stations reduced their abundance by 81.2% (± 2.5% SE) and 72.7% (± 1.6% SE) respectively. NaNO₂ paste, known as BaitRite, has been registered in New Zealand as a vertebrate toxic agent for controlling possums.