Two soybean varieties (an early-maturing Group V and a later-maturing Group VII) and two cotton varieties (a conventional and a transgenic Bacillus thuringiensis Berliner [Bt]) were grown in adjacent replicated large field plots at two locations for 3 growing seasons. The abundance of commonly-observed lepidopteran pests within these two crops was observed weekly throughout each growing season. The green cloverworm, Hypena scabra (F.); soybean looper, Pseudoplusia includens (Walker), and; velvetbean caterpillar, Anticarsia gemmatalis Hübner, preferred soybeans over cotton at all six test sites. The bollworm complex, Helicoverpa zea (Boddie) and Heliothis virescens (F.), preferred soybeans at one site, cotton at two sites, and no crop preference at three sites. There was no difference in the seasonal mean abundance of the pests between the two soybean maturity groups. A few varietal differences were noted on soybeans on specific sampling dates; however, they occurred when insect numbers were low. Population densities approached economic injury levels on both the early and later-maturing soybean varieties. In cotton, the bollworm complex was significantly more abundant in conventional cotton than in Bt cotton. Although soybean loopers are a pest of both crops, soybeans are preferred when they are planted adjacent to cotton. Given this behavioral response, soybeans might serve as a trap crop to attract soybean loopers into a small planting of soybeans and out of the major planting of cotton.

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