Short-term responses of ground-active beetles to alternative silvicultural systems in the Warra Silvicultural Systems Trial,Tasmania, Australia

The Warra Silvicultural Systems Trial (SST) in Tasmania, Australia provides a framework for investigating the responses of beetles (Order: Coleoptera) to three alternative systems in lowland wet eucalypt forest: aggregated retention; dispersed retention; and understorey islands retained in clearfelled areas. Beetles from three families known to be sensitive to forest management, the families Carabidae (ground-beetles), Curculionidae (weevils) and Leiodidae (fungus-beetles), were collected with pitfall traps prior to harvest, and in the first and third years post-harvest. The retained aggregates in the aggregated retention system maintained beetle assemblages reasonably typical of mature forests, at least in these early years following harvesting. These aggregates appear to provide a stable habitat, with similar species composition in the first and third years post-harvest. In contrast, the harvested areas of the aggregated retention system contained low numbers of beetle species affiliated with mature forest, as did the understorey islands and the dispersed retention system. Relative to clearfelling, all alternative silvicultural systems appeared to be of some benefit to beetles affiliated with mature forest, but aggregated retention retained far greater numbers of these beetles compared to the other systems in Tasmanian wet eucalypt forest.     

Cholecalciferol-induced bait shyness in possums (Trichosurus vulpecula)

Cholecalciferol (vitamin D₃) is used in a variety of bait formulations to control populations of the brushtail possum (Trichosurus vulpecula), an introduced pest that seriously damages and threatens primary production and native biota in New Zealand. In cage trials, possums readily ate sublethal baits containing either an estimated LD₁₅ or LD₄₀ dose of cholecalciferol, leading to a depression of appetite that lasted for 7-15 days. When lethal quantities of baits were presented 21-30 days after the initial LD₁₅ or LD₄₀ baits, 40 and 88% of possums survived, respectively, compared with a 21% survival rate among naive possums, and bait consumption was also reduced among survivors of the initial baits. Subsequent switching of the bait base to a gel was partially successful in overcoming bait shyness, killing 40% of one group (formed by pooling the original groups), while switching both the bait type (to gel) and the toxicant (to 1080) resulted in a 63% mortality rate in a second group. By comparison, 95 and 100% of naive groups were killed by cholecalciferol and 1080 gel respectively. Practical measures are identified for both avoiding and overcoming bait shyness based on the use of alternative bait types and toxicants.