Quick Dips

When the Hunter Becomes the Hunted

A biological control agent for a New Zealand pasture pest has been found to infect another beneficial insect, and this has led to new collaborative research with a US university.

AgResearch Invermay environmental pest management scientists Dr Barbara Barratt and Colin Ferguson will be working with Dr Jeffrey Lockwood at Wyoming University on the effects of biological control on non-target species.

Scientists in Wyoming are keen to find out whether they have a similar problem of parasitism by biological controls in non-target insects.

There is little of this type of research world-wide, and Barratt is hoping the collaborative approach will lead to the development of improved protocols on testing of biological control agents, and more rigorous quarantine procedures.

The venture follows on from research carried out by Otago University student Ann Cresswell, at AgResearch Invermay recently on a Student Summer Bursary Scheme.

Cresswell confirmed the insect Rhinocyllus conicus, introduced to New Zealand as a biological control against nodding thistle, was being infected by another biological control agent Microctonus aethiopoides. This parasitoid was released to control the lucerne pest Sitona weevil, but parasitism of several non-target host species have been noted.

She found 8% of the Rhinocyllus population was infected with the parasitoid in one of the field sites she sampled, and she was able to infect Rhinocyllus with the parasitoid in laboratory experiments.

The next step is to try and assess the impact the parasitoid is having on Rhinocyllus, to understand how widespread the problem is and what damage is likely to occur. However, it's likely to be too late to prevent further infestations.

AgResearch scientists are also keen to study the impact of such biological control agents on native insects.

To do this, native weevils need to be studied under laboratory conditions, and this is where the work of another Otago University student on the Summer Bursary Scheme comes in.

The weevils obviously have to be in a healthy state to be used in such studies, but little is known about their needs, particularly in what they eat, and how they should ideally be managed. Natasha Grainger spent her summer successfully working out laboratory-rearing techniques for native weevils, something that will prove essential for further weevil studies.