The toxicity of sodium monofluoroacetate (1080) to Huberia striata, a New Zealand native ant

Although many species of native invertebrates have been identified on toxic baits containing sodium monofluoroacetate (1080) following aerial operations for possum control, few quantitative data are available to determine the risk of primacy or secondary poisoning that may result from these exposures. This paper reports on a series of studies conducted to determine the risk of 1080 exposure to one such non-target insect, the native ant Huberia striata. Subsequent risk of secondary poisoning to insectivorous animals is extrapolated. Ants were exposed in the laboratory to cereal baits containing 0.15% sodium monofluoroacetate, with and without alternative sources of food, and mortality was compared with controls after 24 and 48 h. Acute mortality was significantly greater in both exposed groups and ants that died contained 1080 residues, indicating that some ants could consume lethal amounts of 1080 in cereal baits. However, the increase in mortality was relatively small (7% after 24 h and 12% after 48 h), indicating either that palatability of 1080 bait to this species is low, or that the toxin is not readily absorbed from this matrix. Additional trials were conducted to expose ants to 1080 in sugar-water, in order to determine the acute toxicity dose range. The oral LD50 at 48 h was 32 mg kg(-1), which was comparable to previous results obtained for the large-headed weta, Helmideina crassidens. The persistence of 1080 in ants consuming a sub-lethal dose was also determined, in order to assess risks of secondary poisoning to insectivores. Residues in ants receiving approximately 36 mg kg(-1) of 1080 declined rapidly, from a Peak of 5.51 mg kg(-1) 1 day after exposure, to 0.27 mg kg(-1) after 7 days. Potential risks to insectivorous birds were calculated using worst-case exposure assumptions, and were determined to be negligible.