Iodoacetic Acid Alteration of Soybean Resistance to the Cabbage Looper (Lepidoptera: Noctuidae)

Iodoacetic acid, a classical sulfhydryl reagent, elicited increased and decreased soybean preference by cabbage looper, Trichoplusia ni (Hübner), depending on dose, method of application, specific leaf assayed, and time after treatment. Elicitation was achieved by treating only a minor portion of the plant surface area. Larval T. ni feeding preference for soybean leaf tissues was inversely correlated with the combined amount of the major isoflavanoids daidzein and coumestrol. These compounds have demonstrated antifeedant and antibiotic activities in T. ni larvae.