Frequency of resistance alleles to Bacillus thuringiensis-corn in Texas populations of the sugarcane borer, Diatraea saccharalis (F.) (Lepidoptera: Crambidae)

Diatraea saccharalis (F.) is a primary corn stalk borer pest targeted by transgenic corn expressing Bacillus thuringiensis (Bt) proteins in Texas (USA), especially for the Gulf Coast area of the state. To determine if Bt resistance alleles in D. saccharalis were rare in Texas, as defined in the “high dose/refuge” resistance management (IRM) strategy for Bt corn, 473 two-parent field-collected family-lines of four populations collected from the Gulf Coast area were examined for Bt resistance using F1/F2 screens. No major resistance alleles were detected in these family-lines. The estimated frequency for major Bt resistance alleles in D. saccharalis in the Gulf Coast area of Texas was <0.0016 with 95% probability. Six family-lines were identified to possess minor resistance alleles. The overall frequency for minor resistance alleles in the data combined across the four populations was estimated to be 0.0037 with a 95% credibility interval of 0.0015–0.0069. The results of the current F1/F2 screens suggest that major Bt resistance allele frequency in D. saccharalis was low even after 9 years of use of Bt corn in the Gulf Coast area of Texas, which still meets the rare initial resistance assumption of the “high dose/refuge” IRM strategy in this area. The current screens and other published studies indicate that minor resistance alleles in D. saccharalis appear to occur at a higher frequency compared to other corn stalk borer species. The minor resistance alleles may play an important role in resistance evolution to Bt corn in D. saccharalis.