Using mass-emergence devices to introduce an insect biocontrol agent to a new region and assist its dispersal

Incursions of exotic herbivorous insects into New Zealand’s pastoral systems rely on the introduction of suitable biological control agents to suppress pest populations and reduce their damage. In such situations a mass-emergence device can be used to release introduced biological control agents. Such devices are designed to confine large numbers of parasitised hosts but allow adult parasitoids to escape after they eclose. In this study a mass-emergence device was developed to release an Irish strain of Microctonus aethiopoides (Hymenoptera, Braconidae) into areas of the South Island of New Zealand where the clover pest Sitona obsoletus Gmelin (Coleoptera, Curculionidae) had recently become established. Two laboratory trials confirmed that a mesh size of 900 µm completely contained the host S. obsoletus whilst allowing M. aethiopoides adults to freely enter and exit the device. They also confirmed that parasitised S. obsoletus lived long enough in the device to allow the parasitoid to complete its development. The device was then used to release M. aethiopoides at 13 sites throughout the South Island. Establishment of the parasitoid was confirmed at 12 of the 13 release sites.