Long-term changes and host plant differences in the incidence of parasitoids attacking Helicoverpa spp. (Lepidoptera: Noctuidae) in agricultural landscapes in eastern Australia: Parasitoids of Helicoverpa in eastern Australia

Transgenic (Bt) varieties have improved the control of key insect pests, Helicoverpa spp. (Noctuidae), and reduced pesticide use within Australian cotton crops. Approval to use Bt cotton varieties in Australia required assurance that they would have no significant adverse impact on non-target invertebrates resident in cotton fields. However, little is known of any influences that Bt cotton might have on non-target invertebrates, especially beneficial species, found elsewhere in cotton production landscapes. We collected large numbers of Helicoverpa eggs, larvae and pupae in various major crop types in several cotton production regions in eastern Australia over 26 years and reared them to determine parasitoid frequencies. In addition, more limited collections were made on minor crops, exotic weeds and native vegetation (the latter also surveyed in inland Australia). The most common parasitoids found in crops included Trichogramma spp. and Chelonus spp. (for eggs), Microplitis demolitor, Heteropelma scaposum, Chaetophthalmus sp. and Carcelia sp. (for larvae) and H. scaposum and Ichneumon promissorius (for pupae). Larval parasitoid communities on weeds were similar to those found on crops. Greater parasitoid frequencies were often found in eggs, larvae and pupae of Helicoverpa in crops surveyed after the advent of Bt cotton, compared with earlier years. Similar patterns were found for larvae on the common weed, Echium plantagineum, and native daisies (Asteraceae). No negative associations involving parasitoids and the use of Bt cotton were found.