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 agent | Description |
| Broom psyllids | Broom 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 beetle | The larvae feed on broom seeds slowing the rate at which broom spreads. |
| Broom leaf beetle | Adults and larvae feed on the leaves, growing tips and soft green stems of broom. |
| Broom shoot moth | The larvae feed on the soft new growth ring-barking stems |
| Broom gall mite | These tiny mites feed inside stems causing broom to produce galls. Broom plants heavily infested with galls can die. |
| Broom twig miner | The larvae feed on stems causing whole bushes to die when plants become |
Biocontrol of ragwort
| Control agent | Description |
| Ragwort flea beetle | One 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 moth | This 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 agent | Description |
| Green thistle beetle | Both 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 |
Biocontrol of clover root weevil
An Irish strain of the parasitic wasp Microctonus aethiopoides parasitizes the clover root weevil.
For more information
If you're interested in learning more about biocontrol, please contact our biosecurity team.
