Identification and distribution of oviposition stimulants for monarch butterflies in hosts and nonhosts

Abstract

Flavonol glycosides that act as oviposition stimulants for monarch butterflies were surveyed from a range of asclepiad hosts and some nonhosts. Major stimulants also were identified as quercetin-3-O-(2″-O-β-xylosyl)-β-D-galactoside and quercetin-3-O-β-D-galactoside from Asclepias syriaca and A. incarnata, respectively. The flavonol glycosides in A. curassavica, A. tuberosa, A. incarnata, A. syriaca, A. humistrata, A. albicans, A. eriocarpa, Calotropis procera, Cynanchum acutum, Vincetoxicum (Cynanchum) nigrum and in nonhosts Hoya australis and Nerium oleander were compared and characterized by HPLC and spectral studies. There was great variation in quercetin glycoside content. On the basis of the sugar moieties attached to quercetin, the asclepiad glycosides were classified broadly as those containing: (1) galactose, glucose, and rhamnose; (2) galactose, glucose, and xylose; and (3) galactose, glucose, xylose, and rhamnose. In most cases, galactose was attached to the 3-O-position (1″) of quercetin and other sugars were attached either to the 2″ or 6″ position of galactose. The sugars of triglycosides were attached at both 2″ and 6″ positions. A geographical pattern of flavonol distribution that may have affected the evolution of host recognition by the butterflies is suggested.