Poisonous personalities: Does exposure to a vertebrate pesticide bait, brodifacoum, alter the behaviour of Wellington tree weta?

Adele Parli 1, Anne Besson 1, Priscilla Wehi 2, Sheri Johnson *1

1 University of Otago
2 Landcare Research

Eligible for student prize

Vertebrate pesticide baits are commonly used in New Zealand to control introduced mammalian predators, primarily to protect endemic avian species. Consumption of these baits by non-target species including birds and invertebrates has been observed in a number of studies. In weta, an endemic orthopteran and known consumer of the bait, limited studies suggest that pesticides do not significantly affect mortality. However, no studies have investigated whether the baits alter behaviour of these insects. We tested whether consumption of a widely dispersed pesticide, brodifacoum, influences behavioural aspects of Wellington tree weta, Hemideina crassidens. A sample of 34 H. crassidens were collected from weta motels stationed in Wellington; 17 were placed in a control group, fed on a diet of apples, cat food and leaves, and 17 in a treatment group, fed on the same diet, supplemented with brodifacoum bait pellets. Using video recordings and Ethovision behavioural quantification software, differences in activity (distance travelled, velocity of movement and exploratory range), refuge-seeking behaviour (number and duration of refuge visits, and urgency to seek refuge), aggression (response to facial probe) and emergence (whether the weta has emerged from their refuge at three points of the day) between the two groups were measured. Behavioural assays were repeated at four evenly spaced intervals over fourty days in order to test for cumulative effects of bait exposure. We anticipate that our study will provide important insight into how pesticide baits might influence the natural behaviour of weta, as traits like activity, emergence and aggression undoubtedly influence foraging, mating, competitive interactions and anti-predator responses.

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