ABSTRACT

Bollworm and tobacco budworm populations were evaluated for resistance to CryIAc endotoxins using an incorporated diet bioassay. Mortalities were assessed following a seven day exposure period. CryIAc endotoxins were less effective against bollworm larvae as compared to tobacco budworm larvae. Bollworm LC₅₀ values ranged from 42 ppm to 145 ppm. An LC₅₀ value of 1.0 ppm was recorded for the tobacco budworm population. These values were approximately 2-3 times greater than LC₅₀ values obtained from comparable populations collected between 1996 through 1999. It is imperative that Bt resistance monitoring remain a priority for future studies.