Biocontrol
Biological control or biocontrol is the use of one organism to control the numbers of another.
Unwanted or introduced species can have a huge impact on Aotearoa New Zealand’s environment, and native flora and fauna. Chemicals such as pesticides or poisons can get rid of these species, but are often bad for the environment or affect other species. Alternatives such as trapping, culling or weeding can be time consuming and may only have a tiny impact on the pest population.
Clover root weevil and a parasitoid wasp
Parasitoid wasps lay their eggs in insects. When the larvae hatch, they kill the insect by eating it from the inside out.
A successful biocontrol programme reduces or removes the need for other controls.Learn more about biocontrol in Bioforce – breeding bugs for biocontrol.
Getting rid of weeds
In Aotearoa, biocontrol agents have been used to control the spread of weeds. For example, six different biocontrol agents currently control the spread of gorse – a prickly and invasive weed introduced from Scotland. The small red spider mite has been the most successful of these biocontrol agents as it can eat enough gorse to reduce the plants’ growth and spread.
Honshu white admiral butterfly
The Honshu white admiral butterfly was introduced to New Zealand in 2014 as a biocontrol control for Japanese honeysuckle (Lonicera japonica).
Protecting pasture from pests
Biocontrol can also be used to control insect pests that destroy farmland. The clover root weevil is a pest that was accidentally introduced to New Zealand in the late 1990s and has degraded pasture, especially in the Waikato, where it thrived. The introduction of a tiny wasp from Ireland is now helping to control clover root weevil numbers. Find out more about in this article, Irish wasp to the rescue.
Ryegrass is an important food for grazing stock in New Zealand. A type of fungus, called an endophyte, is being used to protect ryegrass from attack by insect pests, like the Argentine stem weevil and black beetle. Find out more about in this article, Amazing ryegrass.
In 2006 the green thistle beetle, Casida rubiginosa, was selected by Landcare Research Manaaki Whenua after it was found to be the most effective insect in reducing the spread of the Californian thistle – a weed species that costs farmers millions each year in lost production. It was first released in a controlled test in 2007, then released to other areas in Aotearoa. It has been monitored since then, proving to be moderately successful.
Californian thistle
Californian thistle is widespread throughout New Zealand pasture and during its seasonal peak, covers 12% and 6% of grazed land on sheep and sheep/beef farms, respectively, resulting in revenue loss. The green thistle beetle (Cassida rubiginosa) was released in 2007 to help the fight against this invasive weed.
The possum problem
The possum is one of New Zealand’s worst pests. Possums have a detrimental effect on the environment – eating native forests, spreading disease and preying upon native birds. At present, possum numbers are controlled with a combination of poison (1080) and trapping. Scientists are currently researching effective and humane alternatives for controlling possum numbers.
Introduced pests
Introduced pests impact New Zealand’s biodiversity. This image shows a possum and ship rat raiding a nest.
One biocontrol strategy being investigated is the development of immunocontraceptives that use baits, bacteria, viruses, or parasitic worms. These immunocontraceptives prevent the possums from producing offspring by making them sterile.
At AgResearch in New Zealand, they are looking at using a parasitic worm to prevent possums from producing offspring, see our content on the biological control of possums.
Monitoring biocontrol
Introducing a new organism to an environment must only be done after careful consideration to ensure risks to the environment or other species are minimal. In New Zealand, all applications to introduce new organisms are carefully considered by the Environmental Protection Authority who consult with experts and the general public.
Benefits of biocontrol
Val Orchard from ERMA explains how new organisms are sometimes used in New Zealand to control the levels of other organisms.
(Note: ERMA was disestablished in June 2011 and its functions were incorporated into the Environmental Protection Authority (EPA).)
Related content
This article outlines some initiatives working to achieve New Zealand Government’s vision of becoming predator-free by 2050.
Biocontrol was a potential answer to the controversy surrounding 1080. Read about 1080 in this introductory article.
Student activity
In our Biocontrol in action unit plan, students carry out a practical investigation to help AgResearch scientists monitor the spread of a tiny wasp and its success as a biocontrol agent for clover root weevil. This can be adapted for other biocontrol agents.
Useful links
The Pest detective is an online guide to help identify the signs left by pest animals. Developed by the National Pest Control Agencies (NPCA) in partnership with the Ministry for Primary Industries, TbFree New Zealand, the Department of Conservation, and Local Government New Zealand, with substantial sponsorship.
The Biological control agents section on the Environmental Protection Authority (EPA) website explains what biological control agents are, how they work, and the EPA's role in ensuring they are safe for Aotearoa New Zealand.
