Susceptibility of southwestern pink bollworm to Cry2Ab
Gopalan Unnithan, firstname.lastname@example.org, Timothy Dennehy, email@example.com, Sarah Brink, n/a1, Brook Wood, n/a1, Yves Carričre1, Bruce Tabashnik1, Larry Antilla, firstname.lastname@example.org, and Mike Whitlow2. (1) University of Arizona, Dept. of Entomology, Extension Arthrhopod Resistance Management Laboratory, 410 Forbes Building, Tucson, AZ, (2) Arizona Cotton Research and Protection Council, 3721 E Weir Avenue, Phoenix, AZ
Susceptibility of pink bollworm (PBW), Pectinophora gossypiella, to the Bt toxin Cry2Ab2 was evaluated on collections made in the Southwestern U.S. in 2001 and 2002 and contrasted with laboratory strains. PBW were collected from cotton fields, cultured in the laboratory, and tested using diet-incorporation bioassays. A total of 6 collections in 2001 and 14 collections in 2002 were successfully reared and bioassayed. Significant differences between strains in susceptibility to Cry2Ab2 were found each year, though the range of susceptibility was substantially greater in 2001 than in 2002. LC50 estimates of strains ranged from 0.220 to 4.56 µg Cry2Ab2/ml and 0.0840 to 0.723 µg Cry2Ab2/ml in 2001 and 2002, respectively. Only one field strain, a collection from Tornillo, Texas, was substantially less susceptible to Cry2Ab2 than was the laboratory strain, AZP-R, which was highly resistant to Cry1Ac. Based on these baseline responses, concentrations of 1.0 and 10 µg Cry2Ab2/ml diet have been identified for routine monitoring of pink bollworm. The proposed diagnostic doses will be employed in monitoring of populations beginning in 2004, but may be revised based on information generated in 2005 and 2006. Selection of 2001 and 2002 strains with Cry2Ab2 is underway in the laboratory but has not yielded intense resistance to Cry2Ab2. Thus, at this time we have no indication of significant resistance of Southwestern pink bollworm to the second Bt toxin being deployed in transgenic insecticidal cotton.