Monitoring the susceptibility of the southwestern corn borer, Diatraea grandiosella to Cry1Ab and Cry1F toxins

Resistance monitoring strategies to delay the onset of resistance to transgenic maize depend on the effectiveness of resistance monitoring programs capable of early detection of resistance, which allow selected management strategies to be implemented before control failure occurs. To monitor the susceptibility of the southwestern corn borer (SWCB), Diatraea grandiosella, a serious pest in the southern United States, to Bacillus thuringiensis (Bt) toxin in transgenic maize, SWCB populations were collected from areas where the selection pressure for resistance is the greatest, i.e. the areas with the highest market penetration of Bt corn hybrids and/or the areas with the highest insecticide application. In this report, six to eight field populations of the SWCB were collected from two regions with high Bt-corn penetration rate and assayed along with a lab colony to determine susceptibility (larval mortality, larval growth inhibition and response to diagnostic dose) to Cry1Ab and Cry1F toxins. The assay data between 2000 and 2007 were then compared and discussed for any signs of changes in the susceptibility of SWCB to Cry1Ab and Cry1F toxins from the SWCB field populations.