PHENYLPROPENOID PHENOLICS IN SWEETBAY MAGNOLIA AS CHEMICAL DETERMINANTS OF HOST USE IN SATURNIID SILKMOTHS (CALLOSAMIN)

Host plant chemistry can play an important role in determining the evo lution of host use patterns in herbivorous insects by influencing host selection, consumption, and assimilation of foliage. We used a compar ative approach to test the hypothesis that specialist herbivores of sw eetbay magnolia (Magnolia virginiana) possess adaptations that allow t hem to overcome chemical deterrents or toxins that prevent herbivory b y unadapted herbivores. The three silkmoth species in the genus Callos amia can be collectively regarded as specialists on magnoliaceous host s; however, only the monophagous C. securifera is able to complete dev elopment on sweetbay magnolia, its natural host. In laboratory assays with intact foliage, both C. angulifera and the polyphagous C. prometh ea fed readily on sweetbay but were unable to survive past the third i nstar. Two neolignan compounds, magnolol and a biphenyl ether, were fo und to reduce neonate growth and survival of unadapted herbivore speci es when painted on acceptable host leaves at concentrations similar to those found in sweetbay foliage. Both compounds significantly reduced neonate growth of C. angulifera and C. promethea but had no effect on the sweetbay specialist, C. securifera, indicating that the latter sp ecies possesses the unique ability in the genus to tolerate, metaboliz e, or otherwise circumvent the phytochemical defenses of this host.