GREENBUG (HOMOPTERA, APHIDIDAE) BIOTYPES - SELECTED BY RESISTANT CULTIVARS OR PREADAPTED OPPORTUNISTS

Future advances in wheat, Triticum aestivum L., and sorghum, Sorghum b icolor (L.) Moench, resistance to greenbug, Schizaphis graminum (Ronda ni), will likely come from introduction of resistance transgenes into high-performance cultivars. First-generation resistance transgenes wil l be single genes that impart antibiosis traits (similar to Bacillus t huringiensis endotoxins in transgenic corn, Zea mays L.). This approac h to pest management is incompatible with interpretations of simulatio n models that predict that deployment of antibiosis resistance control led by single genes drives the development of new, virulent pest bioty pes. 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 greenbugs on wheat and sorghum were examined to understand the rel ationship between the deployment of plant resistance and the developme nt of new greenbug biotypes. From this analysis, there was no relation ship between the use of resistant wheat and the development of new gre enbug biotypes. For sorghum, with only 3 of the 11 biotypes could ther e be any correlation between the use of resistant hybrids and the deve lopment of new biotypes. Even with these 3 biotypes, no clear cause-an d-effect relationship was established. Based on analysis of these spec ific insect-plant interactions, we propose that future plant resistanc e efforts focus on the use of the most effective resistance genes, des pite past predictions of what effect these genes may have on greenbug population genetics.