Master of Science (MS)



Document Type



The bollworm’s, Helicoverpa zea (Boddie), inherent tolerance to the Bacillus thuringiensis toxin expressed in Bollgard® cotton and its ability to exploit numerous hosts has caused the Environmental Protection Agency to re-evalute the refuge component of the resistance management strategy. The goal of this project was to evaluate selected alternate host crops as supplemental non-cotton refuges for bollworm. The relative density, temporal occurrence, and life stage synchrony for bollworm larvae and adults was studied in Bollgard® cotton, Bollgard® cotton non-Bollgard® cotton, field corn, grain sorghum, and soybean. Native populations of bollworm larvae were monitored June to September during 2002 and 2003 in 0.1011-hectare plots in Northeast Louisiana and in commercial fields in Rapides, Concordia, Richland, and Tensas parishes. Bollworm larval occurrence varied considerably among all sites and crops based upon crop phenology, local environment, cultural production practices, and pest management strategies. Records of larval collection ranged from entirely absent in a sample to collections over a period of seven weeks. Peak densities in Bollgard® cotton were recorded from the 5 nodes above white flower (NAWF) to 1 node above cracked boll (NACB) growth stages, in non-Bollgard® cotton during the 7 NAWF to 1 NACB stages, in field corn during the R2-R5 growth stages, in grain sorghum during growth stages 4 to 9, and in maturity group (MG) 6 soybean during the R1-R6 growth stages. No larvae were observed in MG 4 soybean or in Bollgard® 2 cotton. Larval productivity was generally lowest in Bollgard® cotton fields and highest in grain sorghum and field corn, but larval development in the latter host crops was not consistently in temporal synchrony with that in Bollgard® cotton. The only host crops that exhibited temporal synchrony of larvae to that in Bollgard® cotton was non-Bollgard® cotton and MG 6 soybean. Bollworm adults were monitored with pheromone-baited wire cone traps at the interfaces of Bollgard® cotton and alternate crop hosts at the commercial field sites. During 2002 and 2003, totals of 39,356 and 42,552 adults were collected across all sample sites. Bollworm adult occurrence and total densities were generally similar among traps at all crop interfaces.



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Committee Chair

B. R. Leonard



Included in

Entomology Commons