Few insect herbivores utilize Magnolia virginiana (sweetbay) as a hostplant, one being the sweetbay silkmoth, Callosamia securifera (Saturniidae). However, closely related species suffer 100% mortality on this plant. Preliminary phytochemical work indicates that mortality is due to at least two insecticidal compounds, magnolol and biphenyl ether. This study will characterize physiological/biochemical adaptations of C. securifera to Magnolia by comparing its detoxification mechanisms with those of two congeners unable to tolerate this host's chemicals. In vitro and in vivo experiments will be used to identify enzymatic detoxification systems. In addition, because the three Callosamia species appear to have recently diverged and have some overlap in host use, possible tradeoffs in digestive efficiency and detoxification enzyme activity that may have favored hostplant specialization in the genus will be tested. Specifically, predictions that 1) specialists have higher digestive efficiency than generalists and 2) generalists have higher levels or 3) higher inducibility of broad substrate-specificity detoxification activity than specialists will be tested. With the detailed characterization of specific detoxification mechanisms used by C. securifera to cope with toxins in its host, it may be possible to formulate better hypotheses concerning biochemical tradeoffs associated with host specialization.
