Greenbug (Homoptera: Aphididae) Biotypes: Selected by Resistant Cultivars or Preadapted Opportunists?

Abstract

Future advances in wheat, Triticum aestivum L., and sorghum, Sorghum bicolor (L.) Moench, resistance to greenbug, Schizaphis graminum (Rondani), will likely come from introduction of resistance transgenes into high-performance cultivars. First-generation resistance transgenes will be single genes that impart antibiosis traits (similar to Bacillus thuringiensis endotoxins in transgenic corn, Zea mays L.). This approach to pest management is incompatible with interpretations of simulation models that predict that deployment of antibiosis resistance controlled by single genes drives the development of new, virulent pest biotypes. This dichotomy must be addressed if full advantage is to be taken of the new, powerful tools of molecular biology for plant protection against insects. In this study, the specific insect-plant interactions of green bugs on wheat and sorghum were examined to understand the relationship between the deployment of plant resistance and the development of new green bug biotypes. From this analysis, there was no relationship between the use of resistant wheat and the development of new green bug biotypes. For sorghum, with only 3 of the 11 biotypes could there be any correlation between the use of resistant hybrids and the development of new biotypes. Even with these 3 biotypes, no clear cause-and-effect relationship was established. Based on analysis of these specific insect-plant interactions, we propose that future plant resistance efforts focus on the use of the most effective resistance genes, despite past predictions of what effect these genes may have on greenbug population genetics.