Thursday, 24 April 2008

A first for Otautau and Southland

In December 2007 a site near Otautau was selected for the release of a new insect to aid in the fight against broom (Cytisus scoparius). The broom leaf beetle (Gonioctena olivacea) is a broom specialist and cannot eat any of our native plants including our native brooms (Carmichaelia spp.). Although this insect was released in Canterbury in 2006 this is the first time it has been released in Southland. Fifty male and fifty female beetles were released in a large patch of broom - this site will be checked again in spring/summer 2008 to see if the population has become established. This release is part of the Biological Control of Weeds Programme run by Environment Southland. Biological control (or biocontrol) was recently defined as:

“(T)he use of living organisms to suppress the population density or impact of a specific pest organism, making it less abundant or less damaging than it would otherwise be.”

Eilenberg, J., Hajek, A. and Lomer, C. (2001). ‘Suggestions for unifying the terminology in biological control.’ In: BioControl 46.

Above: A male broom leaf beetle enjoying freedom and a bite to eat at the new release site north of Otautau (female beetles are green and a little larger)

In New Zealand biocontrol research is carried out by Landcare Research/Manaaki Whenua. The Environmental risk Management Authority ERMA) has a very stringent process in place to ensure that any introductions of new organisms into New Zealand will be safe and have no unexpected consequences. Before the broom leaf beetle could even be brought to New Zealand it had to undergo thorough testing and be placed on a starvation diet (!) to make sure that it would only damage the desired plant. Results found that broom leaf beetle may feed on tree lucerne (Chamaecytisus palmensis) if it emerges from hibernation early, but this minor damage was considered acceptable if broom can be brought under control. Biocontrol is not a complete solution as insects that specialise in one plant species will not kill their host. However, by reducing the vigour of plants or their ability to produce seed biocontrol agents can help reduce the impact of weeds. The best things about biocontrol agents is they seek out the weeds themselves, they are natural, they only damage the target plant and they work for free!

Recently a community group was formed to promote the use of biocontrol agents in Te Anau. To find out more or join the Te Anau Biocontrol Group contact: Jesse Bythell -

For more information about biocontrol in Southland contact Keith Crothers (Senior Pest Plant Officer) at Environement Southland - (03) 211 5115

To learn more about the science behind biocontrol go to the Landcare Research page:

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