Master of Science (MS)



Document Type



During 2001-2003, distribution of heliothine- (bollworm, Helicoverpa zea [Boddie], and tobacco budworm, Heliothis virescens [F.]) injured bolls in a transgenic Bacillus thuringiensis Berliner (Bt) Bollgard® and non-Bt refuge cotton system was evaluated in several experiments. Heliothine-damaged bolls were significantly higher and seedcotton yields were lower in the non-Bt refuge than in the Bollgard® areas of fields. The highest probability in occurrence of damaged bolls was at sites near the center of the non-Bt refuge. Number of damaged bolls and probability values describing occurrence decreased from the center of the refuge to sites near the interface (adjacent rows) of the non-Bt refuges and Bollgard® fields. The lowest occurrence of injury was detected at those sites in the Bollgard® fields farther away from the non-Bt refuge. The spatial variation in seedcotton yields across the Bollgard® and non-Bt refuge areas indicated no consistent trends with the exception that seedcotton yield was consistently lower at sample sites in the Bollgard® fields adjacent to the non-Bt refuge compared to the mean yield for the entire Bollgard® sample sites. Pheromone-baited wire cone traps also were used to quantify heliothine adult dispersal in Bollgard® and non-Bt refuge areas. Traps were placed on the field margins of these areas at pre-determined sites starting in the center of the non-Bt refuge and continuing at intervals across the Bollgard® field for 2.4 to 3.5 km. Both species were captured in all traps, but mean numbers of bollworms were higher than that for tobacco budworm. Tobacco budworm captures were consistently higher in traps located closer to the non-Bt refuge, but bollworm captures were not influenced as much by the location of the non-Bt refuge as were tobacco budworm. In addition, the frequency of tobacco budworm adult captures declined as trap distance increased from the refuge. These data serve to explain the distributions of the heliothine species and injury in non-Bt refuges and Bollgard® cotton fields and provide additional information for the future development of Bt-resistance management strategies in transgenic crops.



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Committee Chair

B. Rogers Leonard



Included in

Entomology Commons