ARS | Publication request: Baseline Suscepitibility of the Tobacco Budworm (Lepidoptera: Noctuidae) to the CrylF Toxin from Bacillus thuringiensis

Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 15, 2007
Publication Date: December 3, 2007
Citation: Blanco, C.A., Storer, N.P., Abel, C.A., Jackson, R.E., Leonard, R. 2007. Baseline Suscepitibility of the Tobacco Budworm (Lepidoptera: Noctuidae) to the CrylF Toxin from Bacillus thuringiensis. Journal of Economic Entomology. 101(1): 168-173

Interpretive Summary: In order to help preserve the viability of agricultural biotechnology, proper screening for Bacillus thuringiensis (Bt)-resistance relies on the segregation of putative resistant insects and a method that can discriminate their Bt-resistant from their Bt-susceptible alleles. The first component (segregation of alleles) can be achieved by a second generation (F2) screen that effectively ‘separates’ homozygous resistant, homozygous susceptible and heterozygous insects. A well-calibrated discriminating concentration of Bt (second component) could than identify these genotypes in laboratory bioassays. In order to find the appropriate discriminating concentration for an F2 screen, it is necessary to test field-collected and laboratory colonies. This study reports the susceptibility of 15 field-collected and two laboratory colonies to one Bt protein (Cry1F) finding a diagnostic concentration (100ng/cm2) that would allow to monitoring for Bt resistance for the newest Bt cotton cultivars introduced (1995) in the agricultural market (WideStrike®).

Technical Abstract: Transgenic cotton lines expressing both Cry1F and Cry1Ac insecticidal proteins from Bacillus thringiensis (Bt) have been commercially available in the US since 2005. Both Bt proteins are highly effective against tobacco budworm (Heliothis virescens F.) and other lepidopteran pests of cotton. While Cry1Ac has been available in Bt cotton since 1996, the Cry1F component is relatively new. As part of the pro-active resistance management program for Cry1F/Cry1Ac cotton, a susceptibility monitoring program is being implemented. Baseline variation in the susceptibility to Cry1F in field populations of tobacco budworm was measured. There was a three-fold variation in the amount of Cry1F needed to kill 50% of the neonates from 15 different field populations. Future variation in response in the on-going monitoring program can be compared to this baseline variation. A candidate diagnostic concentration was determined that may be efficiently used to identify individuals that potentially carry major alleles conferring field-relevant resistance to Cry1F before such alleles spread through field populations.