Investigations into the biological control of Nezara viridula (L.) by the egg parasitoid Trissolcus basalis (Wollaston) in eastern Australia

Abstract

In Australia, the green vegetable bug, Nezara viridula (L.) (Hemiptera: Pentatomidae), has reputedly been brought under widespread biological control through the importation and release of several strains of the scelionid egg parasitoid Trissolcus basalis (Wollaston) (Hymenoptera: Scelionidae). Despite persistent claims of successful biological control, N. viridula is considered a serious pest of soybean, Glycine max (L.) Merril. This project was initiated to determine the role that introduced egg parasitoids play in the biological control of N. viridula, especially with relation to its pest incidence in the soybean cropping areas of eastem-Australia. As a first step in this project a review of the available literature was carried out. It soon became apparent that the information available was not only insufficient for research purposes, but also often inaccurate. For these reasons, a critical review of N. viridula biological control in Australia was undertaken for the first time. With access to unpublished file material of the agencies that imported and released parasitoids, I could analyse all available information on the source of parasitoids introduced into Australia, the specific identification of the parasitoids, the numbers of parasitoids reared and released, and their establishment and impact in the field. The results of my review demonstrate that: (a) there is little evidence to support claims of successful biological control of N. viridula; and (b) it is probable that at least two species of parasitoid were released into Australia incorrectly named as T. basalis. This interpretation conflicts with established views that lauded the success of the project, and in particular the beneficial action of T. basalis. These findings directed my subsequent research effort along two main paths. The first of these concentrated on gathering evidence to support or deny the claims made for successful biological control of N. viridula in Australia. A nation-wide mail survey, with the majority of returns coming from the eastern states, showed that N. viridula is currently considered a significant pest of numerous crops in a broad belt extending from south-east Queensland, through inland New South Wales and ending in northern Victoria. Although the evidence is indirect, such a widespread pest distribution is not consistent with an interpretation of successful biological control.