Characterization of Soybean Looper (Lepidoptera: Noctuidae) Tolerance to Bollgard® Cotton: Implications for Resistance Management

The soybean looper, Pseudoplusia includens (Walker), is an occasional pest of cotton and an annual pest of soybean in the southern United States. The development of resistance by soybean looper to the Bacillus thuringiensis Berliner Cry1Ac protein in Bollgard® cotton could potentially influence the efficacy of foliar B. thuringiensis products in soybean. Soybean looper larvae and pupae collected from plots of Bollgard cotton weighed less than larvae and pupae collected from non-Bollgard cotton. Soybean loopers collected from non-Bollgard and Bollgard cotton were maintained separately in the laboratory. No differences were observed in the susceptibility of the subsequent generation (F₁) of soybean looper larvae from non-Bollgard and Bollgard cottons to Cry1Ac based on concentration-mortality data. Neonates from each of these colonies were allowed to complete development on non-treated and Cry1Ac-treated (1.0 μg/ml) meridic diet. Larval weights at 9 d and pupal weights were lower on Cry1Ac-treated diet than on non-treated diet. There were no apparent vigor differences in the two colonies based on development on non-treated diet. In addition, developmental times of larvae from both colonies were longer on Cry1Ac diet than on non-treated diet. These data indicate that development of soybean looper on Bollgard cotton has no effect on the tolerance of subsequent soybean looper generations to Cry1Ac.