Brushtail possums (Trichosurus vulpecula) were introduced to New Zealand from Australia about 150 years ago, and now occupy 95% of the country. More than NZ$70 million is spent annually trapping and poisoning possums for bovine Tb management and to protect native biota and ecosystems. Biological control is being researched as an alternative approach. We are evaluating the potential of the possum-specific intestinal nematode Parastrongyloides trichosuri to be genetically modified to act as a transmissible vector of biological control processes, such as immunosterility. Surveys based on faecal egg counts of Southland and Otago in the South Island. The reasons for the restricted South Island distribution are unclear, but the simplest explanation is a recent introduction of the parasites. In the North Island, prevalence of infection varies seasonally, being highest in autumn, and is higher in older (>2 years) than younger possums. Prevalence appears uniform spatially, at least along 24 km transects across large tracts of North Island native forest. To understand the dynamics and spread of the parasite, we released the wild-type form of the parasites into a population of free-living, parasite-naïve possums at a single site at near Pakawau, northwest South Island. In the 4 years since its release, mark-recapture live trapping has demonstrated that the parasite has persisted at the original release site. Surveys at fixed remote sites indicate that parasite-infected possums now occur over the surrounding 8,000 ha. The seasonal pattern of infection in possums at a site where they were infected naturally mirrors that of possums at the release site. We have now identified a naturally marked strain of the parasite that will be released at the original infection site (subject to approval) to study invasion of already infected populations by a novel strain. This will help us better evaluate the likely outcome of the release of a genetically modified strain and the efficacy of such a biological control system.
|Author||Cowan, P., Ralston, M. and Grant, W.|
|Secondary title||13th Australasian Vertebrate Pest Conference|
|Place published||Wellington, NZ|
|Control method||Biological Control|