Biocontrol

What is ‘Biocontrol’? 

A biological control, or ‘biocontrol’, involves using one living organism to manage another. 

In a plant’s native environment (country of origin), its spread is typically kept in check by predators and diseases that have evolved alongside it. These natural enemies are often highly specialised to attack only that specific plant. When the plant is introduced to a new environment or has been brought in from overseas, it can escape its natural predators, and it can spread quickly – a phenomenon known as ‘ecological release.’

In some special cases, we can import the missing natural predators of an introduced plant to slow its spread and support other weed control efforts. Currently, 400 biocontrol agents are actively working across New Zealand, controlling 133 different weed species.

Recruiting new agents 

We do not carry out the research required to introduce new biocontrol agents. Instead, we seek the view of stakeholders, including iwi and hapū, to determine whether a particular biocontrol agent is acceptable for release. Our role is to support monitoring and aid the spread of biocontrols that have already passed through the biocontrol process.

The biocontrol process

Before any biocontrol organism can be imported or released in New Zealand, it must receive approval from the Environmental Protection Authority (EPA). To get approval, a comprehensive case must be presented to the EPA, weighing the pros and cons of each candidate species. This is a thorough process that involves public consultation and incorporates mātauranga Māori.

To introduce a new biocontrol in New Zealand, researchers must first determine if there are any existing predators of the target weed. There’s little value in reintroducing an organism that’s already present or in releasing a new agent that would compete with existing insects or diseases that are already managing the weed. Next, field surveys, scientific literature, and museum specimens are used to discover what attacks the weed in its home country.

Once the most effective predators are identified, researchers shortlist species that will only attack a limited range of plants. This is typically straightforward, as most plant-eating insects and diseases only feed on one or two host plants. Even so, rigorous experiments are needed to make sure. Potential agents are kept alongside native and economically significant plants to confirm they won't attack these, even if no other food is available. 

Once permission is granted to bring a new biocontrol into New Zealand, a population is kept in quarantine to ensure that no other unwanted organisms are present. After this quarantine period, the new biocontrol can be reared in larger numbers and released at selected sites across the country. 

We play a key role in monitoring biocontrol agents after their release. We track their establishment, evaluate how far they’ve spread from the release sites, and assess their effectiveness in controlling the target weed. Our goal is to determine how successful the biocontrol has been in reducing the health and abundance of the weed species.

Other biocontrol agents are known to be at work in the region, either seen directly or detected through eDNA. These include the Cinnabar moth, Old Man’s Beard leaf miner, Hemlock moth, and Giant Willow Aphid wasp.