Biocontrol

What is Biocontrol?

Biocontrol uses the natural enemies of a pest to reduce the damage it causes. We release biocontrol insects in Southland for broom, ragwort and thistles to help reduce the harm these pests cause.

All potential biocontrol agents undergo rigorous testing before applications to the Environmental Risk Management Authority are made to bring them into New Zealand. Only those organisms which feed specifically on their targeted host are released. Much of the biocontrol research done in New Zealand is carried out by Landcare Research.

Biocontrol agents

Biocontrol of broom

Control agentDescription
Broom psyllidsBroom psyllids feed on the sappy new growth causing plants to wilt. The damage caused to broom plants can be severe where psyllid numbers are high.
Broom seed beetleThe larvae feed on broom seeds slowing the rate at which broom spreads.
Broom leaf beetleAdults and larvae feed on the leaves, growing tips and soft green stems of broom.
Broom shoot mothThe larvae feed on the soft new growth ring-barking stems
Broom gall miteThese tiny mites feed inside stems causing broom to produce galls. Broom plants heavily infested with galls can die.
Broom twig minerThe larvae feed on stems causing whole bushes to die when plants become

Biocontrol of ragwort

Control agentDescription
Ragwort flea beetleOne of the first biocontrol agents to be released in Southland. The larvae of this beetle feed on the roots and crown of ragwort rosettes, reducing their vigour and ability to flower. Initially this beetle was slow to build up numbers in Southland, but now there are over 100 release sites across the region. Many of these sites are relatively new, but at several older established sites ragwort levels have been significantly reduced.
Ragwort plume mothThis moth was released to compliment the work of the ragwort flea beetle as it can tolerate wetter conditions. The caterpillars of this moth feed inside the leaves, crown and roots of ragwort plants. Two or three caterpillars feeding on a plant can kill it. Even if the feeding damage does not kill a plant outright, it will reduce its ability to flower and seed

Biocontrol of thistle

Control agentDescription
Green thistle beetleBoth the adults and larvae feed on a range of thistle species. Adults can live for up to 80 weeks and a female beetle can lay 1000 eggs over her lifetime. This agent reduces the vigour of thistles by feeding on the leaves; when beetles are very numerous they can completely defoliate plants
Californian thistle stem minerThis tiny weevil has not been used as a biocontrol agent anywhere else. It was first released here in 2009, so it is still too soon to know how much damage it will cause. The adult weevils lay eggs inside thistles stems, and after the larvae hatch they either burrow up through the stems or down into the roots. This type of feeding damage complements that of the green thistle beetle as both agents work together to undermine the health of thistle plants.

Biocontrol of clover root weevil

An Irish strain of the parasitic wasp Microctonus aethiopoides parasitizes the clover root weevil.

Get biocontrol insects from us

We supply biocontrol agents free of charge to Southlanders, though availability is determined each year by the amount able to be collected from established populations.

If you're interested in receiving one or more insects when they're available, please contact our biosecurity team.

Page reviewed: 02 May 2016 9:45am