Effect of racemic, (+)- and (-)-gossypol on survival and development of Heliothis virescens larvae

Gossypol is a constituent of the lysigenous foliar glands of cotton plants and is also found in glands in cottonseed. Gossypol exists as enantiomers because of restricted rotation around the binaphthyl bond. The biological activities of the enantiomers differ. For example, (+)-gossypol can be fed safely to nonruminants such as chickens, but (-)-gossypol cannot. Most commercial cottonseed contain a (+)- to (-)-gossypol ratio of approximately 3:2. Conventional breeding techniques can be used to develop cottonseed that contains >95% (+)-gossypol. Notably, gossypol protects the plant from insect herbivores. Herein, we report the effect of various forms of gossypol on Heliothis virescens (Fabricius) larvae. Three levels (0.16, 0.24, and 0.32%) of racemic, (+)-, and (-)-gossypol were added to artificial rearing diets and were fed to H. virescens larvae. All 0.24 and 0.32% gossypol diets significantly lengthened days-to-pupation and decreased pupal weight compared with the control. Percent survival was significantly less for larvae reared on diets containing 0.24% of all three forms of gossypol as compared with the control diet. (+)-Gossypol was superior or equivalent to racemic gossypol as measured by the three parameters studied. Higher concentrations of all gossypol forms were required to reduce survival and pupal weights and increase days-to-pupation for larvae of H. virescens larvae compared with the concentration needed to affect larvae of Helicoverpa zea (Boddie), which was studied previously. These results indicate that current efforts to breed cotton lines containing mostly (+)-gossypol in seed should not significantly impair the plant's natural defenses against insects.