The effects of benzoxazinoids on specialist and generalist Diabrotica spp. (Coleoptera: Chrysomelidae)

Benzoxazinoids are secondary metabolites constitutively produced by maize as protective compounds against insect herbivores.  In this study we investigated the role of benzoxazinoids as natural plant defense against the maize specialist Diabrotica virgifera virgifera and a congeneric generalist Diabrotica undecimpunctata howardi.  We hypothesized that both D. v. virgifera and D. undecimpunctata howardi would perform better on non-defended maize than on defended one.   We further hypothesized that, as a specialist that usually feeds on benzoxazinoid-defended maize, D. virgifera virgifera would perform better than the generalist SCR.  To test these hypotheses, we analyzed the survival, growth and development of larvae feeding on 428G maize, which is defective in benzoxazinoid biosynthesis, and H88, the wild type parental line of 428G with normal benzoxazinoid production.  Feeding on maize containing benzoxazinoids imposed no significant cost to the survival, growth and development of either D. v. virgifera and D. undecimpunctata howardi.  Instead of showing improved performance in the absence of plant defenses, D. v. virgifera larvae gained significantly more weight on benzoxazinoid-defended maize.  Our results showed distinct response of specialist and generalist insects to benzoxazinoids.