Frequency of Resistance to <I>Bacillus thuringiensis</I> Toxin Cry1Ab in Southern United States Corn Belt Population of European Corn Borer (Lepidoptera: Crambidae)

Abstract

The high-dose refuge resistance management strategy is the main approach used to delay resistance in targeted pests to Bacillus thuringiensis (Bt) toxins in transgenic crops. We used an F2 screen to test a critical assumption of the high-dose refuge strategy, which is that resistance allele (R) frequencies are initially rare (<10(-3)) in Ostrinia nubilalis (Hübner) (Lepidoptera: Crambidae) from the southern Corn Belt. We expanded the methodological scope of the F2 screen so that both males and females may be used to initiate a screen and determined how the results from both sexes may be combined. In total, 62 female and 131 male O. nubilalis lines from Kansas and 39 female and four male lines from Texas were screened. No major resistance alleles were found and estimated R frequency for the southern Corn Belt was updated to between 0 and 0.0044 with 95% credibility. The experiment-wise detection probability was 98.7%. These results suggest the frequency of resistance alleles is low enough that the high-dose refuge resistance management strategy may be effective for delaying resistance evolution in O. nubilalis to Bt corn in the southern Corn Belt.

Global perspectives on field-evolved resistance to transgenic Bt crops: a special collection

“…The extremely low frequency of O. nubilalis alleles conferring resistance to Cry1Ab corn when this transgenic crop was first commercialized and soon after has probably also delayed evolution of resistance in Europe as well as in the United States. No alleles conferring resistance to Cry1Ab corn were detected in F 2 screens of this pest conducted from 1999 to 2005 in 2156 lines from Europe (France, Italy, Germany, and Slovakia) and from 1996 to 2003 in 933 lines from the United States, which together represent 12,356 alleles screened , 2000, Bourguet et al 2003, Stodola et al 2006, Engels et al 2010. These results indicate the Cry1Ab resistance allele frequency in O. nubilalis was well below 0.001.…”

Understanding successful resistance management

“…Although potential changes in frequency over time have not been examined, no major Cry1Ab resistant alleles have ever been recovered using this technique confirming that the frequency of alleles conferring resistance to Cry1Ab expressing plants is below 10 -3 in all the populations examined to date. [61][62][63][64] Similar estimates of Cry1F resistance frequencies from field populations of O. nubilalis have yet to be reported. However, based on the ease with which resistance can be selected for in the laboratory and the identification of the same resistance allele among field populations, it appears likely that the frequency of Cry1F resistance is higher than 10 -3 in field populations.…”