What is biocontrol?
Don McKenzie, the Northland Regional Council's Biosecurity Team Leader explains what biocontrol is all about and how it is used in Northland:
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Don McKenzie, NRC Biosecurity Team Leader
"Biocontrol (biological control) is the use of naturally occurring enemies and diseases to control pests and weeds. Following introduction to an area, the biocontrol agents may need assistance to spread, but when sustainable populations have established and become widespread they carry on working against the target weed indefinitely. Biocontrol is not designed to totally eradicate a species but aims to keep populations at low levels. It is the most cost effective method of control over a wide area and at remote sites."
How are biocontrol agents found?
The first step in finding biocontrol agents is a survey of the natural enemies of the target weed or pest in New Zealand and/or overseas. Natural enemies found in New Zealand can be redistributed around Northland. Suitable overseas candidates from areas with a climate matching Northland’s are tested in a secure quarantine facility to determine whether they will attack any native New Zealand species or any species that is of economic value. If it can be shown that the biocontrol agent attacks only the target species, an application for release from quarantine is made to the Environmental Protection Authority (EPA), followed by consultation with the public and stakeholders. When approval is given, the biocontrol agent can be multiplied for release.
What about biocontrol of insects?
Many predators and parasitoids (those that kill their host) exist in the wild, in your backyard, orchard or vegetable garden and with careful nurturing can be encouraged to kill your insect pests. The main groups of insect biocontrol agents are parasitic wasps, parasitic flies, predators such as ladybirds, midges, hoverflies, earwigs, lacewings, spiders, mites, mirid and damsel bugs. Diseases that affect insects include fungi and bacteria, and there are internal parasites which can make the pest feel decidedly unwell.
Predatory bug feeding on a caterpillar (photo: Plant and Food Research)
The 11-spotted ladybird (photo: Plant and Food Research)
What weed biocontrol agents are available?
Weed biocontrol insect agents include seed feeders (maggots, grubs, caterpillars), leaf feeders (caterpillars, sawflies), leaf miners (maggots, caterpillars), shoot feeders (caterpillars), raspers (thrips), sap suckers (psyllids, mites), stem borers (caterpillars, maggots, grubs), crown feeders (grubs), twig miners (caterpillars), bark strippers (beetles), root feeders (grubs). The combined effect of at least two or more of these agents can reduce the growth and dispersal of a target weed
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Wooly bear caterpillar - ragwort leaf feeder (photo: Landcare Research)
Which insect biocontrol agents have been successful in Northland?
Few realise it, but Northland is a battleground for a little-known and largely unseen war between a host of tiny insects and fungi and some of the region's worst weeds. There have been many successfully introduced insect biocontrol agents in action. Two parasitic wasps now control armyworms and cutworms in maize, as well as tomato fruitworm in vegetables. The parasitic wasp, Thripobius javae, now keeps numbers of greenhouse thrips low where insecticide sprays are not used. This thrips is a serious pest in the avocado and citrus orchards. Wasps that kill Argentine stem weevil and clover root weevil in pasture are now established and the ladybird, Cleobora mellyi, which feeds on eucalypt and blackwood pests is now resident in Northland following its relocation from Marlborough.
In addition, Northland is home to 10 species of ladybirds, several species of predatory mites, the Tasmanian lacewing, predatory mirid and damsel bugs, and the generalist parasitoid wasp, Meteorus pulchricornis. All of these are exerting pressure on horticultural and garden pests in Northland. There are at least 10 species of parasitic wasps affecting a range of citrus pests such as scales, aphids, leaf rollers, mealybug and lemon tree borer. Some biocontrol agents are available commercially for use in greenhouse crop production. The Mexican dung beetle is found in the volcanic soils of Whangarei and south of Kaikohe, and is contributing to the biological removal of dung in pasture.
What are the successful weed biocontrol agents in Northland?
In total, 21 new insects and mites have been deliberately introduced to control gorse, ragwort, thistles, broom, alligator weed, mist flower, buddleia, Mexican devil weed, St John’s Wort and boneseed. Sixteen have established and seven are widespread throughout Northland. The ragwort flea beetle is now found throughout Northland and delivering good control of ragwort. Diseases have also been successful in controlling weeds in Northland. Mistflower is controlled by a fungus and the blackberry rust blown over from Australia is having a detrimental effect on blackberry. A rust of smilax/bridal creeper has been discovered and is now available for redistribution.
How much do we spend on biocontrol in Northland?
A total of $50,000 a year is invested in Northland’s biocontrol by a collective of 13 regional councils and the Department of Conservation. Collectively, group members fund the national biocontrol programme to the tune of about $670,000 annually. The programme is managed by Landcare Research and provides research, quarantine facilities and management of releases of the agents within New Zealand. The Northland Regional Council also funds individual projects such as the introduction of the clover root weevil parasitoid wasp. The Council has recently contributed $2,000 to the gum leaf skeletoniser biocontrol project being undertaken by Scion Research.
Where to from here?
A number of new agents are in the pipeline for introduction against insect pests and weeds. These include a pirate bug which is being considered for introduction from the South Island and a parasitoid wasp which attacks gum leaf skeletoniser and is in quarantine at Scion.
What biocontrol agents are in the pipeline for release?
Gum leaf skeletoniser caterpillars and parasitoid cocoons (photo: Scion Research)
A programme for the introduction of dung beetles into New Zealand has been initiated which will accelerate the burial of dung in pasture, increase nutrient recycling and reduce faecal contamination of waterways.
Investigations into a further 12 insects and six diseases as biocontrol agents for eight Northland weeds are at various stages of the introduction process. Approval for the release of a lace bug against tobacco weed has been granted by EPA and three beetles that feed on tradescantia are currently being held in quarantine. Surveys for natural enemies of ginger in China are continuing. Studies on rusts of moth plant and boneseed are being conducted by Landcare Research and a rust which damages lantana is ready for release.
Moth plant rust (photo: Landcare Research)