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 operatio ns for possum control, few quantitative data are available to determine the risk of primacy or secondary poisoning that may result from these exposure s. This paper reports on a series of studies conducted to determine the ris k of 1080 exposure to one such non-target insect, the native ant Huberia st riata. Subsequent risk of secondary poisoning to insectivorous animals is e xtrapolated. Ants were exposed in the laboratory to cereal baits containing 0.15% sodium monofluoroacetate, with and without alternative sources of fo od, and mortality was compared with controls after 24 and 48 h. Acute morta lity was significantly greater in both exposed groups and ants that died co ntained 1080 residues, indicating that some ants could consume lethal amoun ts of 1080 in cereal baits. However, the increase in mortality was relative ly small (7% after 24 h and 12% after 48 h), indicating either that palatab ility 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 rang e. 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 per sistence of 1080 in ants consuming a sub-lethal dose was also determined, i n 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 day s. Potential risks to insectivorous birds were calculated using worst-case exposure assumptions, and were determined to be negligible.