Susceptibility of Cry1Ab maize-resistant and -susceptible strains of sugarcane borer (Lepidoptera: Crambidae) to four individual Cry proteins

[Display omitted] ► Six Diatraea saccharalis strains were established from survivors on Bt maize. ► All six strains were highly resistant to Cry1Ab, Cry1Aa, and Cry1Ac proteins. ► The six strains exhibited only a low level of cross-resistance to Cry1F protein. ► The survival on Bt maize is a result of resistance to Cry1Ab in the plants. ► Pyramiding Cry1A and Cry1F into a plant could be a good strategy. Sugarcane borer, Diatraea saccharalis (F.), is a major target of Bt maize in South America and many areas of the US mid-south region. Six laboratory strains of D. saccharalis were established from six single-pair F2 families possessing major resistance alleles to Cry1Ab maize hybrids. Susceptibility of the six strains was evaluated on diet treated with each of four purified trypsin-activated Bt proteins, Cry1Ab, Cry1Aa, Cry1Ac and Cry1F. Bt susceptibility of the six strains was compared with that of known Cry1Ab-susceptible and -resistant strains of D. saccharalis. At least two of the six strains demonstrated a similar level (>526-fold) of resistance to Cry1Ab as shown in the known Cry1Ab-resistant strain, while resistance levels were relatively lower for other strains (116- to 129-fold). All the six strains were highly cross-resistant to Cry1Aa (71- to 292-fold) and Cry1Ac (30- to 248-fold), but only with a low level to Cry1F (