3. Biological Control Of Possums
The introduced Australian brushtail possum (Trichosurus vulpecula) is a very serious pest in New Zealand. It causes extensive damage to indigenous forests and acts as the major vector of bovine Tb to cattle and deer.
Forest ecosystems are being drastically altered by the selective attention of possums that can eliminate favoured browse-species from whole tracts of forest. Possums also prey on birds.
The potential reduction in returns from agricultural production, should restrictions on access for meat and dairy products be imposed by our trading partners due to the presence of bovine Tb, could be up to $500 million annually.
Currently about $45 million is spent annually on poisoning and trapping possums. However, this level of expenditure is not sustainable and these methods of control are becoming less socially and politically acceptable. Around $15 million is spent annually on research into control of possums and bovine Tb.
Research into possum biocontrol as a long-term cost-effective solution to the possum problem was initiated in 1993. The expectation is, however, that control will be, for the foreseeable future, dependent on a number of technologies used in an integrated manner.
The research into biological control of possums, funded through Vote: Agriculture was initiated following a National Science Strategy Committee (NSSC) meeting, held in October 1992, at which clear research priorities for biological control were established. Priorities were reviewed at NSSC workshops in 1995 and 1997.
The programme has received $2 million a year since July 1993 and has guaranteed funding only until the end of June 1999. MAF is seeking funding from Government for a further three years in order to pursue the promising lines of research which have been identified.
Most of the research programmes follow one of two directions for possum biocontrol. The first involves targeting physiological pathways, such as the possum reproductive system, while the second is looking for potential vectors. Vector organisms could, possibly, be genetically manipulated in order to enable them to spread disruptive genes throughout the possum population. These genes would be expressed as biochemicals that would interfere with possum reproduction or health.
Most of the physiological research is focusing on the reproductive system. This includes studies on gametes, fertilization, embryonic development and endocrine control of reproduction. Essentially, the search is on for possum-specific physiological pathways that could be targeted for disruption and at this stage much of the research is fundamental.
Surveys of parasites and pathogens of possums have been carried out in Australia and New Zealand. One species of nematode parasite, which was found in the highest prevalence in Australia, appears to be absent here. Work is continuing to see whether it would be beneficial to introduce the nematode that could simply add to the load of parasites in the possum population or be used as a vector of disruptive genes.
In New Zealand the distribution of parasites was very uneven with some possum populations being free of significant parasites. Consideration is being given to introducing the missing parasites to these populations.
The most pathogenic agents found in possums to date are viruses. One causes a syndrome known as wobbly possum disease (WPD) while another causes a range of symptoms including diarrhoea. The virus responsible for WPD has been characterised and appears to be related to Borna virus that infects a number of animal species including humans. The relationship between the viruses is thought to be distant but work aimed at clarification of the relationship is in progress. Neither of the possum viruses, noted above, has been shown to be important in wild possum populations but both decimate captive colonies.
An adeno virus that is possum-specific has also been identified and it is thought to have potential as a vector if it can be grown in the laboratory.
Very good progress has been made in developing an understanding of fundamental possum physiology and several pathways have been identified which could be targeted for disruption. The most promising area is female reproductive physiology and a number of novel approaches to disruption are currently being researched both in Australia and New Zealand.
Progress is monitored and research reports assessed by six reviewers. Two members of the group, Drs Paul Livingstone (AHB) and Peter Kettle (MAF) are members of the NSSC. The four other members are Drs Ken McNatty, Richard Sadleir and Hugh Davies and Professor John Marbrook who are contracted by MAF to provide a technical overview of the research falling within their speciality fields.
Contact for Enquiries
Farm Monitoring Programme Manager
Monitoring and Evaluation
MAF Policy
PO Box 2526
Wellington
NEW ZEALAND
Phone: +64 4 894 0623
Fax: +64 4 894 0741
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