F₂ screen for resistance to a Bacillus thuringiensis-maize hybrid in the sugarcane borer (Lepidoptera: Crambidae)

A novel F₂ screening technique was developed for detecting resistance in sugarcane borer, Diatraea saccharalis (F.), to transgenic Bacillus thuringiensis (Bt)-maize expressing the Cry1Ab insecticidal protein. The F ₂ screening method involved (i) collecting larvae from maize fields; (ii) establishing two-parent families; (iii) screening F₂ neonates for survival on Bt-maize leaf tissues; and (iv) confirming resistance on commercial Bt-maize plants. With the F₂ screening method, 213 iso-line families of D. saccharalis were established from field collections in northeast Louisiana, USA and were screened for Bt resistance. One family was confirmed to carry a major Bt resistance allele(s). In a laboratory bioassay, larval mortality of the Bt-resistant D. saccharalis on Bt-maize leaf tissues was significantly lower than that of a Bt-susceptible strain. This Bt-resistant D. saccharalis population is the first corn stalk borer species that has completed larval development on commercial Bt-maize. The F₂ screening protocol developed in this study could be modified for detecting Bt resistance alleles in other similar corn stalk borers, such as the European corn borer, Ostrinia nubilalis (Hübner), and the southwestern corn borer, D. grandiosella Dyar.