Date: 17 May, 2011

Trans-Tasman Hunt For Guava Moth’s Enemies

Researchers are about to embark on a $26,000-plus trans-Tasman search for natural enemies of the guava moth, whose larvae currently infest and ruin a range of soft fruit and nuts from Northland to the Waikato.

An Australian native, the moth (Coscinoptycha improbana) is thought to have blown across the Tasman in its adult form in the late 1990s. It is not a pest in its home country and biosecurity experts here want to know why.

The hope is they may be able to use that knowledge to control the insect in New Zealand, especially as climate mapping indicates that unchecked, guava moth will eventually colonise all of the North Island and the northern part of the South Island.

“The first step is to try to discover and identify what natural enemies it has in Australia as it’s likely these are what are keeping its population low there,” Cable Bay, Northland-based entomologist Dr Jenny Dymock says.

Dr Dymock, who works with the Northland Regional Council, is managing the guava moth biocontrol project, while the council’s Biosecurity Senior Programme Manager Don McKenzie is chairing the more than a dozen-strong project team.

The regional council and the New Zealand Feijoa Association have just secured $16,450 funding from the Ministry of Agriculture’s Sustainable Farming Fund to help meet some of the initial $26,000 costs of a project expected to take at least another 12 to 18 months. The pip fruit, summer fruit and macadamia industries are also contributing funding, as are the Waikato Regional and Auckland Councils.

Dr Dymock says because they develop within affected fruit, guava moth larvae are not easily targeted by insecticides. Other options, including removing windfall fruit, have failed to contain the pest.

The larvae render fruit inedible with their excrement and can also lead to the development of damaging moulds and fungi. They can also cause premature fruit drop.

She says pheromone traps will be used shortly to confirm guava moths’ presence in three parts of eastern Australia, which are also home to laboratories with facilities that can be used as part of the study. Research by Dr Dymock in 2004 has already confirmed the moth’s presence at a final, fourth Queensland site.

In autumn next year, a variety of fruit crops infested with guava moth will be collected from the four Australian sites and allowed to develop in special moth-proof cages, with any parasitoids found collected. Similarly guava moth eggs will be collected from the wild at one site to see if they are subject to any form of parasitism.

Further research will then be able to be done to see if any of the parasites can eventually be used as biological control agents targeting guava moth.

Mr McKenzie says it could be another several years before any guava moth biocontrol agent or agents developed as a result of the research can be released in New Zealand.

However, while they were generally not cheap to develop because of the care that must be taken to ensure other non-pest species wouldn’t be affected, biocontrol agents still offered a cost-effective, non-chemical and environmentally-friendly way to target pests.

Northland is already home to a number of biocontrol agents including insects, fungi and rusts which attack a variety of pest plants and insects including clover root weevil, mistflower, gorse and ragwort.

Mr McKenzie says the regional council is also involved in trialling pheromone attractants aimed at disrupting guava moth mating activity.

He says until a biocontrol agent for guava moth is developed, the Northland Regional Council will continue to advise the public and fruit and nut growers about other tactics to try to reduce the pest’s impact.

These include simple measures from covering fruit trees with protective mesh to ensuring good orchard hygiene.

Biosecurity officers can be contacted via the council’s freephone (0800) 002 004.


ENDS

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