Chemical ecology of the tiger swallowtail: mediation of host use by phenolic glycosides
Subspecies of the eastern tiger swallowtail butterfly exhibit striking differences in their ability to use quaking aspen (Populus tremuloides) and other members of the Salicaceae as larval host plants. Papilio glaucus canadensis survives and grows well on aspen, whereas Papilio glaucus glaucus does not. In earlier studies we isolated a crude fraction of aspen compounds that exhibited activity against P. g. glaucus and identified the components as a suite of four phenolic glycosides (salicin, salicortin, tremuloidin, and tremulacin). This study was designed to identify the specific phenolic glycosides, or interactions among glycosides, responsible for the differential abilities of Papilio subspecies to utilize quaking aspen. We bioassayed the glycosides individually and in combination against both Papilio subspecies, using neonate survival trials and fourth—instar feeding trials. None of the compounds or combinations of compounds negatively affected the survival, growth, consumption rates, or digestibility/conversion efficiencies of P. g. canadensis, or 72—h survival rates of P. g glaucus. Salicortin and tremulacin significantly increased fourth—instar duration and decreased growth rates for P. g. glaucus, primarily by reducing consumption rates. Salicin and tremuloidin showed no negative effects. Combinations of glycosides containing salicortin and tremulacin decreased larval survival and a dramatically lowered growth rates by decreasing both consumption rates and food conversion efficiencies. Observations of treated larvae indicated that these glycosides may have caused gut lesions. The active component of salicortin and tremulacin is a cyclohexeone saligenin ester, and its activity is synergized in tremulacin by the presence of a benzoyl ester on the same molecule. We propose that differences in the susceptibilities of P. g. canadensis and P. g. glacus to the active phenolic glycosides are due to differences in activity of their carboxylesterase detoxication systems.
Lindroth, Richard L.; Scriber, J. Mark; Hsia, M. T. Stephen. 1988. Chemical Ecology of the Tiger Swallowtail: Mediation of Host Use by Phenolic Glycosides. Ecology. 69 (3): 814-822.