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Influence of Bt Cotton on Beneficial Arthropod Populations

N. B. Van Tol and G. L. Lentz


Studies were conducted on paired farm fields and in large research plots in 1996 and 1997 to determine the impact of Bt cotton on beneficial arthropod populations. Sweep samples were taken to determine relative numbers of beneficials, and terminal evaluations were used to detect Heliothine pressure. Squares were removed for evaluation of Heliothine feeding and boll weevil feeding/oviposition. Insecticide sprays were applied to on-farm fields in response to plant bug, Heliothine complex, and boll weevil in 1996. In 1997, Dimilin was used to reduce boll weevil oviposition, but one on-farm site was sprayed with methyl parathion to control weevil populations. Total numbers of beneficial arthropods were greatly reduced in 1996, due to insecticide effects, when compared to 1997. Beneficial arthropod populations rarely differed significantly between Bt and non-Bt sites in either year. In 1996, there were significant differences in the number of larvae greater than 1/4 inch found on terminals and in the number of Heliothine damaged squares in Bt and non-Bt varieties.

Reprinted from Proceedings of the 1998 Beltwide Cotton Conferences pp. 1052 - 1054
©National Cotton Council, Memphis TN

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Document last modified Sunday, Dec 6 1998