Toxicity of cholecalciferol to rats in a multi-species bait

Abstract

The effectiveness of Feracol®, a possum control paste bait containing 0.8% cholecalciferol, as a rodenticide has been assessed in cage and field trials. Caged rats were provided with toxic bait in choice and no-choice tests. Feracol® was readily eaten when presented as the sole food source or with other food, and was effective at killing rats in both situations. Wild-caught and laboratory rats (n = 35), comprising both ship (Rattus rattus) and Norway rats (R. norvegicus), were presented with 30 g of Feracol® alone or with an equivalent toxic bait over 48 h. Thirty-four rats died in an average of 4.0 days. Having established that the paste, originally designed for possum control, is also an effective rodenticide for rat control, field trials were initiated with the paste delivered in the field in Philproof® and Striker® bait stations. Monitoring of rat numbers before and after application of toxic bait was undertaken at three trial sites, Lions Hut, Mangaone and Pakoakoa, in Te Urewera National Park in the North Island of New Zealand. Rat population density was assessed using tracking tunnels. Philproof® bait stations containing 200 g of Feracol® were placed 50 m apart on grids at Lions Hut and monitoring was undertaken at one location per hectare using tracking tunnels. At Mangaone and Pakoakoa, two Striker® bait stations containing 18 g of Feracol® were sited at 25-m intervals on lines 150 m apart, and monitoring was undertaken with five lines of 10 tunnels at 50-m intervals. At Lions Hut, rat tracking decreased from 78% to 3% of tunnels tracked; at Mangaone the reduction was 51% to 0%; and at Pakoakoa from 36% to 0%. These trials demonstrate that Feracol® is effective at reducing both moderate and high concentrations of ship rats in the Philproof® and Striker® bait station delivery systems.