Landcare Research - Manaaki Whenua

Landcare-Research -Manaaki Whenua

Heat Turned Up on Chilean Weevils

Hernan Norambuena and Randall Milne (Environment Southland) discussing release sites for the new Darwin’s barberry weevils.

Hernan Norambuena and Randall Milne (Environment Southland) discussing release sites for the new Darwin’s barberry weevils.

Since our last article on Darwin’s barberry (Berberis darwinii) back in August 2011 (Issue 57), the Environmental Protection Authority (EPA) has given approval to release two weevils that attack this invasive species.

The application to release the first biocontrol agents to be used against Darwin’s barberry anywhere in the world was put forward by Environment Southland on behalf of the National Biocontrol Collective. With that hurdle out of the way the next step was to begin mass-rearing and releasing the two weevils. The seed weevil (Berberidicola exaratus), as its name suggests, lays eggs inside barberry fruit with larvae feeding on the seeds. The flower bud weevil (Anthonomus kuscheli) lays its eggs in the new barberry flowers. Lindsay Smith, who is leading the project, has noticed that feeding by adult flowerbud-feeding weevils significantly damages new flowers on potted barberry in containment. But he said, “It’s the larvae that will really deal to the flowers – eating the entire contents of the flower and then pupating in the remaining capsule.”

Our colleague Dr Hernán Norambuena, who undertook the weevils’ host range safety testing in Chile, collected populations of the weevils from their native range in central to southern Chile and delivered them to Lincoln in October last year. Hernán’s visit was made possible thanks to an AGMARDT fellowship that will allow to him to come to New Zealand twice to assist with the project. “Hernán has been helping to fi ne-tune the weevil rearing, and his expertise has been extremely valuable,” said Lindsay.

The weevils must initially come into containment and be reared through one generation there. This is so we can check for disease and any parasitoids that might have come along for the ride. However, synchronising the arrival of the weevils in New Zealand with the flowering of potted plants in containment has proved challenging. Despite starting out with a large number of Darwin’s barberry plants, few of them have cooperated, either refusing to grow in pots or to flower. “It is interesting how difficult it can be to deliberately grow some weeds!” commented Lindsay. So in the end there were only a limited number of flowers available to the newly imported weevils and even fewer fruits and seeds. However, supplementary feeding with cut flower stems and fruit seems to have worked and there are now larvae reaching maturity. “It was a great moment when I dissected my first weevil-infested barberry fruit in containment and found a large larva and all the seeds chewed on,” said Lindsay.

The synchronicity issues have meant that there won’t be enough weevils to begin releases this autumn, as initially hoped, so the plan is to now begin releases next spring. This also means that the weevil releases can be better timed to coincide immediately with the availability of flowers and fruits in the field, which will increase the likelihood of establishment. The lessons learnt this season should put us in good stead for greater success next spring. Further shipments from Chile next spring will also help to boost numbers available for release.

This project was funded by the National Biocontrol Collective. Dr Hernán Norambuena’s Visiting Fellowship is funded by the Agricultural and Marketing Research and Development Trust (AGMARDT).