SELECTIVE CHEMICAL DEFENSES OF AN INTRODUCED CRUCIFER AGAINST DIFFERENT LARVAL STAGES OF A NATIVE BUTTERFLY

J.Alan A. Renwick, Wenqing Zhang and Meena Haribal
Boyce Thompson Institute, Ithaca NY 14853, USA

Adults of the indigenous butterfly, Pieris napi oleracea , inthe northeastern United States readily lay eggs on the introduced crucifer,Alliaria petiolata, garlic mustard. However, the larvaegenerally do not survive on this plant. The lack of larval developmentcan be explained by the presence of feeding inhibitors in rosette leavesof the garlic mustard. The bioactivity was obtained in aqueous extractsand was further extracted into butanol. Fractionation of the activebutanol extract by flash chromatography and HPLC has resulted in the isolationof a single compound that deters feeding by 4th instar larvae. However,this compound had no effect on neonate larvae. Instead, neonate feedingwas inhibited by a second compound, which was ineffective against 4th instars. The results suggest that A. petiolata is protected from early andlate instars of P. n. oleracea by two separate compounds. Furthermore, the mechanism of feeding inhibition for the two compoundsappears to be distinctly different.