Cabbage Looper (Trichoplusia ni) larvae were collected from commercial vegetable greenhouse crops in British Columbia, Canada throughout the 2000 and 2001 summer period. Collected larvae were reared in the laboratory to adulthood and the susceptibility of their first generation offspring to Bacillus thuringiensis kurstaki (Dipel) was assayed. The results indicate that greenhouse populations of Cabbage Loopers are developing Bt resistance. All greenhouse populations exhibited higher levels of resistance than the laboratory colony. In 2000, Bt susceptibilities of collected T. ni populations were 4-5, 8-10, and 16-19 times higher than the laboratory reared colony. When comparing mortalities 5 days following Bt exposure, the resistance of one pepper greenhouse T. ni population was 68-fold higher than the laboratory colony. The success of rearing T. ni in the lab appeared to vary with the crop from which they were collected. This finding may indicate that there are fundamental differences between Looper populations collected from different crops. More intensive studies of the evolution of Bt resistance over a growing season and the interaction between Bt and crop effects are needed to develop an appropriate Bt resistance management strategy.
The ESA 2001 Annual Meeting - 2001: An Entomological Odyssey of ESA