Role of cotton trichome density and extrafloral nectar in bollworm (Lepidoptera : Noctuidae) egg parasitism and predation

Abstract

Field, greenhouse and laboratory studies were conducted to determine the effect of cotton trichome density on parasitism and predation of Heliothis zea (Boddie) eggs. In a no-choice field test of three cotton phenotypes differing in trichome density, parasitism of H. zea eggs by Trichogramma pretiosum Riley was 13-fold higher on the Smoothleaf cotton phenotype and 8-fold higher on the hirsute cotton compared to the Pilose cotton. In a free-choice field study comparing two cotton near-isolines, natural parasitism of H. zea eggs by Trichogramma spp. was 3-fold higher on the Smoothleaf phenotype compared to the Pilose phenotype. Further, no-choice greenhouse tests of Smoothleaf, hirsute and Pilose cottons demonstrated that predation of H. zea eggs by Chrysopa rufilabris (Burmeister) larvae improved as trichome density decreased. Laboratory studies showed that cotton leaf trichomes inhibited movement of T. pretiosum and C. rufilabris larvae over leaf surfaces. Thus, reduced trichome density on cotton improves the ability of T. pretiosum and C. rufilabris larvae to find and destroy H. zea eggs. Field, greenhouse and laboratory tests were conducted to determine the effect of nectariless cotton on parasitism and predation of H. zea eggs. Extrafloral nectar was essential to survival of T. pretiosum adults and thus accounted for greater parasitism of H. zea eggs on nectaried vs. nectariless cotton phenotypes. Further, the presence of extrafloral nectar did not adversely affect the functional response of C. rufilabris larvae to its prey, as there were equal number of H. zea eggs destroyed on the nectaried and nectariless cottons. Results from these studies demonstrate positive and negative interactions between host-plant resistance and biological control. The implications of these interactions for integrated pest management and the development of pest resistant cultivars are discussed.