Influence of cotton plant structures on heliothine larval development and the production and infectivity of occlusion bodies of nucleopolyhedrovirus in larvae

Helicoverpa zea (Boddie) and Heliothis virescens (F.), reared on different cotton structures, were studied for larval growth and development, susceptibility to H. zea nucleopolyhedrovirus (HzNPV), and production of occluded virus (OBs). Larval weight of both species after 10 d of rearing differed with larvae on artificial diet having the highest weight and those on square bracts the lowest weight. In both species, pupal weight and length of pupal developmental period were positively correlated with the larval weight, but length of the larval developmental period was negatively correlated with larval weight. Mortality from virus infection of H. zea and H. virescens larvae on squares, square bracts or flowers did not differ significantly among the structures. In both species, the number of viral OBs produced was greater in larvae fed flowers than those fed other structures and was positively correlated with the weight gained by a healthy larva on that plant structure. The mean LC₅₀ for OBs produced in H. zea or H. virescens larvae on square, square bract or flower did not differ significantly. These results indicate that dietary difference in fruiting structures of cotton plants directly affects H. zea and H. virescens larval growth and development and indirectly affects the production of virus by HzNPV-infected larvae.