The efficacy of baits containing 1080 for control of brushtail possums

A significant proportion of brushtail possums (Trichosurus culpecula) in Ne w Zealand survive pest control operations using sodium monofluoroacetate (1 080) baits. To be effective, bait needs to contain an appropriate concentra tion of 1080 and be eaten in amounts lethal to all possums, In our trials, the acute toxicity of 1080 to captive possums was estimated when the toxica nt was included in different bait types, and results compared with publishe d data for 1080 administered in aqueous solutions by oral gavage, The effec tiveness of baits containing different 1080 concentrations, and of differen t palatabilities, was also assessed. Captive possums that fed on baits in t his trial were less susceptible to 1080 (LD50 = 1.5 mg/kg) than in previous ly reported trials where the toxicant was administered to caged possums by oral gavage (LD50 = 0.8 mg/kg; P < 0.001). The differences in the acute tox icity of 1080 in water and in baits ale attributed mainly to the reduced bi oavailability of 1080 in baits. Also in our trial, captive animals feeding voluntarily on baits more closely approximated the status of animals in the wild than when acute toxicity was estimated by anaesthetizing possums and intubating solutions bl oral gavage. Genetic polymorphisms caused some anim als to be much more susceptible to 1080 toxicosis than others. Body mass di fferences cause females and young possums to ingest a higher toxic dose (mg /kg) than adult males, and the concentrations of toxicant affected the amou nts of bait eaten and the resultant mortality. For the range of baits teste d, the palatability of bait was a more important determinant of amounts eat en. and the percentage of possums sublethally poisoned, than was toxicant c oncentration. Possums that ate baits of low palatability and inappropriate 1080 concentration ingested small doses of 1080 and either endured a protra cted time to death or survived. The size and quality of bait have implicati ons for the management of wild populations of possums in different climatic areas where aerial and land-based methods of control are used.