Unseen battle raging in Northland

Increasing numbers of tiny eco-warriors are being conscripted by the Northland Regional Council to battle on its behalf against a host of pest plant and insect enemies.

Biological control is the use of naturally-occurring enemies and diseases to control pests and weeds. It’s not designed to eradicate a species; instead it aims to keep populations at low levels.

Don McKenzie, Biosecurity Senior Programme Manager for the Northland Regional Council, says there’s a surprising range of more than two dozen biological control agents already in use in Northland, with even more likely to be available in the future.

“In the long-term, biocontrol is very cost-effective and environmentally-friendly method of pest control and I believe we will see it used more and more frequently in Northland in the future against an even wider variety of target species.”

“Insects that can be used for biological control of pest plants 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) and root feeders (grubs). “

Mr McKenzie says there are also many predators (like spiders and even ladybirds) as well as parasitoids, which kill their host, that already exist in the wild or in people’s backyards, orchards or vegetable gardens.

“With careful nurturing these can be encouraged to kill your insect pests too.”

He says 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.

Finally, there are diseases that affect insects including fungi and bacteria, as well as tiny internal parasites.

Mr McKenzie says experts often use a combination of two or more biocontrol agents to reduce the growth and dispersal of a target pest plant or insect.

“For instance in Northland we recently released the first clusters of a South American beetle which attacks the leaves of tradescantia (wandering jew). We’re planning to follow this up over the next year or two with the release of two more beetles, one which feeds on tradescantia stems and the other its tips.”

Mr McKenzie says Northland and its ratepayers are also fortunate to have locally-based insect experts living in the region who are able to guide many of the biological control efforts undertaken here.

One such project - a new $26,000-plus trans-Tasman search for natural enemies of the guava moth – has both the council and Jenny Dymock, the Cable-Bay based entomologist it works closely with, in key roles. Dr Dymock is managing the project, while Mr McKenzie is chairing the more than a dozen-strong project team.

An Australian native, guava moth (Coscinoptycha improbana) is thought to have blown across the Tasman in its adult form in the late 1990s and its larvae now infest and ruin a range of soft fruit and nuts from Northland to the Waikato. Despite this, it is not a pest in its home country and biosecurity experts are hoping to discover a natural enemy or enemies in Australia that can eventually be used as a biocontrol agent here.

Mr McKenzie says Northland is already home to at least two dozen insects and mites deliberately introduced to control gorse, ragwort, thistles, broom, alligator weed, mist flower, buddleia, Mexican devil weed, St John’s Wort and boneseed.

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.

Additionally, broom gall mite was released at Kaimaumau just before Christmas, woolly nightshade (tobacco weed) lacebugs have been released at a number of spots this year and a new species of small ladybird, Serangium maculigerum, was released on citrus in Northland just before New Year to feed on the citrus whitefly.

Mr McKenzie says the process from lowly insect or fungus to biological control conscript is a painstaking, lengthy and initially costly one.

“The Northland Regional Council alone typically spends at least $80,000 annually on biological control work and is part of a national collective which leverages more than $600,000 towards this kind of work each year.”

He says the first step in finding biocontrol agents is a survey of the natural enemies of the target weed or pest either here in New Zealand and/or overseas.

While natural enemies already found in New Zealand can usually be redistributed around Northland, it’s different for those from overseas.

“Potentially suitable overseas candidates from areas with a climate matching Northland’s must be extensively 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.”

Mr McKenzie says only when researchers are confident the potential biocontrol agent attacks just the target species alone, an application for release from quarantine is made to the Environmental Risk Management Authority (ERMA), followed by consultation with the public and stakeholders.

“It can take a number of years from when the initial hunt for a biological control agent begins to when approval for its release is ultimately given.”

For more on biological control in Northland, visit: www.nrc.govt.nz/biologicalcontrol