Sodium monofluoroacetate (1080) is still an essential tool for possum control. We have reassessed the fate of this compound in the environment, and found no evidence of water contamination after large-scale possum control operations. The toxin is biodegradable in all living systems and will not accumulate in the food chain. Nevertheless, overreliance on a single toxin for a particular pest, such as 1080 for possum control, is unwise, and we are evaluating alternatives. Possums are susceptible to some non-anticoagulant toxins, including gliftor, cholecalciferol, calciferol, and alpha-chloralose. Of the anticoagulant toxins, brodifacoum is more effective than pindone. Integrated pen and field trials will determine the most cost-effective alternatives to 1080 for use in bait stations and for aerial application. Any alternative toxin will need to be subjected to the same scrutiny as 1080 for its environmental fate and impact on non-target species.

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ABSTRACT:Bovine tuberculosis (Tb), due to infection with virulent Mycobacterium bovis, represents a threat to New Zealand agriculture due to vectorial transmission from wildlife reservoir species, principally the introduced Australian brushtail possum (Trichosurus vulpecula). An oraldelivery wildlife vaccine has been developed to immunize possums against Tb, based on formulation of the human Tb vaccine (M. bovis BCG) in edible lipid matrices. Here BCG bacilli were shown to be stable in lipid matrix formulation for over 8 mo in freezer storage, for 7 wk under room temperature conditions, and for 3-5 wk under field conditions in a forest/pasture margin habitat (when maintained in weatherproof bait-delivery sachets). Samples of the lipid matrix were flavored and offered to captive possums in a bait-preference study: a combination of 10% chocolate powder with anise oil was identified as the most effective attractant/palatability combination. In a replicated field study, 85-100% of wild possums were shown to access chocolate-flavored lipid pellets, when baits were applied to areas holding approximately 600-800 possums/km 2 . Finally, in a controlled vaccination/challenge study, chocolate-flavored lipid vaccine samples containing 10 8 BCG bacilli were fed to captive possums, which were subsequently challenged via aerosol exposure to virulent M. bovis: vaccine immunogenicity was confirmed, and protection was identified by significantly reduced postchallenge weight loss in vaccinated animals compared to nonvaccinated controls. These studies indicate that, appropriately flavored, lipid delivery matrices may form effective bait vaccines for the control of Tb in wildlife.

The risks of vertebrate pesticides to non-target animals are determined by intrinsic susceptibility, the toxicokinetics of the compounds used, and the degree and frequency of exposure. Metabolism and persistence studies coupled with field surveys have provided us with an improved understanding of the toxicokinetics and non-target effects of different anticoagulants. This has enabled improved choice of tools for island versus mainland use in New Zealand, and has stimulated the development of low-residue tools. Brodifacoum is a potent secondgeneration rodenticide used worldwide for commensal rodent control, and has been widely used to eradicate rodents from islands. The risks associated with 'one-off' application of baits containing second-generation anticoagulants for rodent eradication on islands are considered to be outweighed by the potential benefits to their ecosystems. Possums are susceptible to bait containing brodifacoum, but not to first-generation anticoagulants, hence brodifacoum has been the only alternative to 1080 that effectively targets both possums and rodents. On the mainland, contamination of wildlife and game species and secondary poisoning of non-target species has been substantial where brodifacoum has been used repeatedly. We are extending the current range of low residue alternatives to reduce reliance on brodifacoum and sodium fluoroacetate (1080). Currently, suitable alternatives available include encapsulated cyanide Feratox † and cholecalciferol paste Feracol † . Other compounds being developed as alternatives include micro-encapsulated zinc phosphate and low dose cholecalciferol and coumatetralyl, or C'C.

In New Zealand cholecalciferolcontaining baits are used for possum and rodent control We have assessed the primary and secondary nontarget hazards associated with these baits At 2000 mg/kg cholecalciferol had no adverse effects in ducks but some chickens and canaries died Weta and weka were not affected by eating bait containing cholecalciferol In secondary poisoning studies most dogs and cats fed carcasses of possums poisoned with cholecalciferol were unaffected but repeat exposures for 5 days induced some reversible signs of toxicosis in dogs The most distinguishing feature of cholecalciferol is a lower risk of secondary poisoning when compared with 1080 and brodifacoum