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

Abstract

Classical biological control involves introducing natural enemies to new locations, and can often be limited by the expense, and technical and logistical complexity, of collecting, culturing and releasing natural enemies. Our study investigated the potential of mass-emergence devices, which are designed to confine hosts, but not adult parasitoids, for reducing these limitations in a classical biological control programme. The programme introduced a parasitoid from Europe, Microctonus aethiopoides (Hymenoptera, Braconidae), to assist management of an invasive Palearctic weevil that feeds on white clover, Sitona obsoletus Gmelin (Coleoptera, Curculionidae), in New Zealand. M. aethiopoides is an endoparasitoid of the adult stage of S. obsoletus. Laboratory evaluations of device design confirmed that the devices confined S. obsoletus adults, but not M. aethiopoides adults. They also showed both that parasitised S. obsoletus lived long enough in the devices for immature parasitoids to complete their development, eclose and exit the devices, and that M. aethiopoides adults would enter devices and oviposit in unparasitised hosts. In the field, three approaches to using the devices were tested: populating devices with parasitised hosts cultured in the laboratory; populating devices with parasitised hosts collected from the field; and populating devices with unparasitised hosts, placing them in field locations where the parasitoid was established, allowing them to become parasitised by wild parasitoids, then transferring the devices to new release sites. All three approaches were effective for establishing M. aethiopoides at new locations, and offered advantages over standard release methods.