ELEVATED ATMOSPHERIC CO2 EFFECTS ON PHYTOCHEMISTRY, INSECT PERFORMANCE AND INSECT PARASITOID INTERACTIONS

This study was conducted to examine the effects of CO2-mediated change s in tree chemistry on the performance of the gypsy moth (Lymantria di spar L.) and the parasitoid Cotesia melanoscela (Ratz.). We used carbo n-nutrient balance theory to develop hypotheses regarding changes in t ree chemistry and the performance of both insects under elevated CO2. As predicted, levels of foliar nitrogen declined and concentrations of carbon-based compounds (e.g. starch and phenolics) increased under el evated CO2. Gypsy moth performance (e.g. growth, development) was alte red by CO2-mediated changes in foliar chemistry, but the magnitude was small and varied across tree species. Larvae feeding on high CO2 aspe n exhibited the largest reduction in performance, relative to larvae f eeding on birch, oak, or maple. Parasitism by C. melanoscela significa ntly prolonged gypsy moth development and reduced growth rates. Overal l, the effect of parasitism on gypsy moth performance did not differ b etween CO2 treatments. Altered gypsy moth performance on high CO2 foli age in turn affected parasitoid performance, but the response was vari able: parasitoid mortality increased and adult female size declined sl ightly under high CO2, while development time and adult male size were unaffected. Our results suggest that CO2-induced changes in plant che mistry were buffered to the extent that effects on third trophic level interactions were weak to non-existent for the system examined in thi s study.