BACILLUS-THURINGIENSIS RESISTANT COLORADO POTATO BEETLE AND TRANSGENIC PLANTS - SOME OPERATIONAL AND ECOLOGICAL IMPLICATIONS FOR DEPLOYMENT

The Colorado potato beetle is a severe pest of potatoes in the US. It has developed field resistance to almost every insecticide used agains t it, and is considered to be a model species for insecticide resistan ce. We have recently reported the selection of a Bacillus thuringiensi s (Bt) resistant strain of beetle (Bt-R). We have tested this strain a nd susceptible beetles (Bt-S) against transgenic potato plants in 96-h (first instars through adults) and complete development bioassays (se cond instars through adults). The Bt-R strain first instars were almos t as susceptible to transgenic plants as the Bt-S strain, but second i nstars were significantly different from controls in longevity and wei ght gained (P < 0.01). Adult Bt-R beetles averaged 25% mortality over 14 days, and each of the younger instars (fourth, third and second) ex perienced greater mortality. The operational and ecological implicatio ns of potential Bt resistance on deployment of transgenic potato plant s are discussed.