Low-dose cholecalciferol bait for possum and rodent control

Abstract

A new low-concentration formulation of Feracol® paste containing 0.4% concentration cholecalciferol was tested for efficacy against possums in cage trials, and against possums and rodents in a single unreplicated field trial. A new low-concentration 0.4% cholecalciferol cereal pellet was also tested in the field against possums and rodents. 20 wild-caught possums, held in individual cages, were presented with 15 g of 0.4% cholecalciferol paste. Possum body weight, amount of paste eaten and days until death were recorded. The field trial occurred on Banks Peninsula, Canterbury, from September to November 2009, using a treatment site of c. 100 ha and a non-treatment site of c. 200 ha. The treatment site was divided into two even blocks, one for paste and one for pellets. Pre- and post-monitoring were carried out using leg-hold traps for possums, and tracking tunnels for rodents. Of the 20 caged possums, a kill rate of 89.5% with an average time to death of 7.0 days±0.41 SEM was achieved, similar to earlier work on cholecalciferol using a higher concentration. In the field trial pellet treatment block, possum numbers were reduced by 94±11%, mice numbers by 100±0% and rat numbers by 89±12%. In the paste treatment block, possum numbers were reduced by 93±16%, mice numbers by 75±29% and rat numbers by 100±0%. Under the current study conditions, the effectiveness of the new Feracol® paste and pellets containing 0.4% concentration cholecalciferol was comparable to the currently registered 0.8% concentration cholecalciferol Feracol® paste formula, and was effective in controlling multiple pest species while reducing the poisoning risk to non-target species. Replication of this field trial using the new bait matrices is necessary to increase confidence under similar and differing conditions, to ensure that the efficacy seen here is not arbitrary.