BACILLUS THURINGIENSIS CRY1AC RESISTANCE MONITORING PROGRAM FOR TOBACCO BUDWORM AND BOLLWORM IN 2004

Authors: Blanco, Carlos; Mullen, Regina; Abel, Craig; BRADLEY, JULIUR - NC STATE UNIV; ELLSWORTH, PETER - UNIV OF ARIZONA; GREENE, JEREMY - UNIV OF ARKANSAS; HERBERT, AMES - VIRGINIA TECH; LEONARD, ROGER - LOUISIANA STATE UNIV; Lopez, Juan De Dios; Meagher, Robert - Rob; MOAR, WILLIAM - AUBURN UNIV; PARAJULEE, MEGHA - TEXAS AG EXP STATION; RUBERSON, JOHN - UNIV OF GEORGIA; SPRENKEL, RICHARD - UNIV OF FLORIDA

Submitted to: National Cotton Council Beltwide Cotton Conference
Publication Type: Proceedings
Publication Acceptance Date: 12/28/2004
Publication Date: 1/7/2005
Citation: Blanco, C.A., Mullen, R.M., Abel, C.A., Bradley, J.R., Ellsworth, P., Greene, J.K., Herbert, A., Leonard, R., Lopez, J., Meagher Jr, R.L., Moar, W., Parajulee, M., Ruberson, J., Sprenkel, R. 2005. Bacillus thuringiensis cry1ac resistance monitoring program for tobacco budworm and bollworm in 2004. National Cotton Council Beltwide Cotton Conference. p. 1210-1218

Interpretive Summary: The advantages that Cry1Ac-transgenic cotton has brought to many agricultural areas in North America have been documented. The tobacco budworm was the key cotton pest in most of the cotton belt before 1996. In order to control this insect, several applications of synthetic insecticides were made every growing season, ranging from 2-10 depending on the year, type of product and geographical area. This successful technology has replaced all those tobacco budworm-applications due to the high effectiveness of Bt against this pest. Since the economic and environmental (lesser number of insecticide applications) benefits are important to society, the preservation of the effectiveness of Bt cotton is key for this new technology. The US Environmental Protection Agency has identified Bt-resistance as the most important issue for this technology. Monitoring the susceptibility shifts is a useful indicator of the potential development of resistance. Making this the most accurate and time-opportune method is the primary goal of this program. Since 1996, at the time of the commercial introduction of transgenic cotton, the USDA-ARS laboratory in Stoneville, Mississippi began testing the shifts of susceptibility of the tobacco budworm (H. virescens F.) and bollworm (H. zea Boddie) to several Bacillus thuringiensis (Bt) toxins. The primary goal of this program is to cover large geographies and produce information that the registrants of Bt cotton, regulatory agencies and society can use to answer their needs. Since that time, the program has been partially sponsored by those registrants (Monsanto and Dow AgroSciences up to 2004). A 2004 report with major findings follows. Up to this moment, June 2004, no signs of Cry 1Ac-resistance have been observed utilizing the method described below.

Technical Abstract: The susceptibility to Bacillus thuringiensis Cry1Ac protein in the tobacco budworm (Heliothis virescens [F.]) and bollworm (Helicoverpa zea [Boddie]) was tested in populations from 9 cotton-producing states in 2004. The survivorship of larvae obtained from mass mating males captured in pheromone traps near cotton fields (wild strain) with laboratory-adapted females (Cry1Ac-susceptible colony), was determined with 2 diagnostic concentrations for the first (F1) and second (F2) generation of each species plus an untreated control. Survivorship of those larvae was concurrently compared with the survivorship of the Cry1Ac-susceptible laboratory colony. Survival of 19 strains of Heliothis virescens and 37 strains of Helicoverpa zea tested between April and October, 2004 was not elevated above that in the susceptible colony for F1 or F2 generations using current methodology. However, the current method does have limitations, and additions and modifications to that methodology are discussed.