Decreased leaf-miner abundance in elevated CO2: Reduced leaf quality and increased parasitoid attack

Most studies on the effects of elevated CO2 have focused on the effects on plant growth and ecosystem processes. Fewer studies have examined the effec ts of elevated CO2 on herbivory, and of these, most have examined feeding r ates in laboratory conditions. Our study takes advantage of an open-top CO2 fertilization study in a Florida scrub-oak community to examine the effect s of elevated CO2 on herbivore densities, herbivore feedings rates, and lev els of attack of herbivores by natural enemies. Higher atmospheric CO2 concentration reduced plant foliar nitrogen concentr ations, decreased abundance of leaf-mining insect herbivores, increased per capita leaf consumption by leafminers, and increased leaf miner mortality. As suggested by other authors, reduced foliar quality contributed to the i ncrease in herbivore mortality, but only partly. The major factor increasin g mortality was higher attack rate by parasitoids. Thus increasing CO2 conc entrations may reduce the survivorship of insect herbivores directly, by re ducing plant quality, but also indirectly, by changing herbivore feeding an d eliciting greater top-down pressure from natural enemies.