Integration of biological and microbial control of 'Helicoverpa armigera' on transgenic 'Bt' cotton

Abstract

The activity of an insect predator, the green lacewing (Mallada signatus) and a new fungus* was tested against Helicoverpa armigera, Hubner on transgenic Bt cotton compared to its counterpart conventional cotton. Fifty H. armigera neonate larvae were placed at different locations on each potted cotton plant under glasshouse conditions and two green lacewings were released. Within 72 hours, green lacewings reduced the survival of H. armigera larvae from 62% to 37% on conventional cotton and 10% to 5% on Bt cotton. H. armigera moved to reproductive parts on both cotton types and the survival of H. armigera was significantly reduced when green lacewing was present. The effects of Bt toxin and green lacewings acted synergistically on H. armgiera larvae. The fungus was isolated from the eggs of H. armigera in cotton fields in Australia. The pathogenicity of the fungus was tested in the laboratory against H. armigera eggs and larvae. H. armigera eggs or neonate larvae were placed onto cotton leaves before the fungal suspension applied. The fungus killed 42% to 62% H. armigera eggs in different laboratory experiments and also was able to kill over 50% of the neonate larvae. This study provides evidence that green lacewing larvae and this new fungus could be used in combination as biological control agents for the management of H. armigera on cotton, particularly survivors on transgenic Bt cotton. *Due to commercial-in-confidence reasons the name of the fungus cannot be revealed.