STATUS OF PINK BOLLWORM SUSCEPTIBILITY TO BT IN ARIZONA

Authors: PATIN, A - U OF AZ, TUCSON, AZ; DENNEHY, TIM - U OF AZ, TUCSON, AZ; SIMS, M - U OF AZ, TUCSON, AZ; TABASHNIK, BRUCE - U OF AZ, TUCSON, AZ; LIU, YONG-BIAO - UNIV OF AZ, TUCSON, AZ; ANTILLA, LARRY - ACRPC, TEMPE, AZ; GOUGE, DAWN - USDA-ARS, WCRL, PHOENIX; Henneberry, Thomas

Submitted to: University of Arizona Agricultural Experiment Station
Publication Type: Experiment Station
Publication Acceptance Date: 6/1/1999
Publication Date: N/A
Citation: N/A

Interpretive Summary:

Technical Abstract: Statewide monitoring of pink bollworm susceptibility to Bt toxin was conducted in AZ in 1997-1998. A concentration of 10 ug/ml Cry1Ac caused >80% mortality of all field populations. LC50s of AZ populations ranged from 0.35 to l.7 ug Cry1Ac/ml of insect diet. A laboratory strain of pink bollworm (PBW) had an LC50 of 0.53 ug/ml. A selection experiment was conducted in which survivors of bioassays of 3.2 and 10 ug/ml of Cry1Ac from all AZ populations tested in 1997 were pooled and reared for 1 generation on diet containing 10 ug CrylAc/ml. Selection produced a strain of PBW that was 100- to 460- fold less susceptible to Cry1Ac, than were the field populations from which it was derived. Preliminary results from greenhouse evaluations concerning survival of this resistant strain on Bt cotton showed that larvae were able to complete development in bolls of Bt cotton, pupate, and successfully reproduce. The type of resistance we have isolated in the laboratory is likely to negatively impact field performanc of Bt cotton in AZ in the future. We found no evidence that field performance of Bt cotton has yet been compromised. In large field trials, infield refuges of non-Bt cotton were contrasted with the standard, external refuges. During 1997 and 1998, in-field refuge plots yielded comparable to, or better than, plots of 100% Bt cotton yet they produced substantial numbers of pink bollworm late in the season on non-Bt status.