PYRAMIDING CRYIA(B) INSECTICIDAL PROTEIN AND TERPENOIDS IN COTTON TO RESIST TOBACCO BUDWORM (LEPIDOPTERA, NOCTUIDAE)

The development of insect resistance to CryIA insecticidal proteins ex pressed in transgenic cotton, Gossypium hirsutum L., is likely to occu r quickly following commercialization, unless strategies are implement ed to delay pest adaptation. This study was undertaken to determine th e effects of pyramiding (i.e., combining 2 or more resistance traits i n the same plant) the transgenic CryIA(b) insecticidal protein trait w ith the conventional high-terpenoid plant trait on resistance to tobac co budworm, Heliothis virescens (F.), growth, survival, and injury to the plant. The transformed cotton line MON 81 expressing the cryIA(b) gene was crossed to glandless (terpenoid-free), wild-type (normal terp enoid level), and high-glanded (high-terpenoid) plant isolines derived from the 'TAMCOT CAMD-E' and 'Stoneville 213' variety backgrounds. F- 2:4 cotton lines were evaluated in field and laboratory no-choice surv ival and plant injury experiments. In the field no-choice experiment, the CryIA(b) trait alone reduced larval growth, larval survival, and i njury to flower beds, capsels, terminals, and leaves of CryIA(b)-susce ptible and CrpIA(b)-adapted tobacco budworm larvae compared with wild- type cotton. Larval injury to cotton was also reduced by the high-terp enoid trait compared with wild-type cotton, but larval growth and surv ival were not significantly different. In a laboratory no-choice study , survival of CryIA(b)-susceptible larvae was reduced more by pyramidi ng the CryIA(b) protein trait with the high-terpenoid trait in a singl e plant background than by either trait alone when compared with the t erpenoid-free control plants. These results suggest that the relative levels of resistance among the traits were (from highest to lowest): p yramided CryIA(b) + high-terpenoid > pyramided CryIA(b) + normal-terpe noid > CryIA(b) alone > high-terpenoid alone > normal-terpenoid alone > no terpenoid or CryIA(b). These data suggest that pyramiding CryIA(b ) insecticidal protein with high-terpenoid should increase plant resis tance to tobacco budworm and improve the durability of the CryIA(b) tr ait in commercial cotton.