Decreased Leaf-Miner Abundance in Elevated CO 2 : Reduced Leaf Quality and Increased Parasitoid Attack

Abstract

Abstract. Most studies on the effects of elevated CO 2 have focused on the effects on plant growth and ecosystem processes. Fewer studies have examined the effects of elevated CO 2 on herbivory, and of these, most have examined feeding rates in laboratory conditions. Our study takes advantage of an open-top CO 2 fertilization study in a Florida scrub-oak community to examine the effects of elevated CO 2 on herbivore densities, herbivore feeding rates, and levels of attack of herbivores by natural enemies.Higher atmospheric CO 2 concentration reduced plant foliar nitrogen concentrations, decreased abundance of leaf-mining insect herbivores, increased per capita leaf consumption by leafminers, and increased leafminer mortality. As suggested by other authors, reduced foliar quality contributed to the increase in herbivore mortality, but only partly. The major factor increasing mortality was higher attack rate by parasitoids. Thus increasing CO 2 concentrations may reduce the survivorship of insect herbivores directly, by reducing plant quality, but also indirectly, by changing herbivore feeding and eliciting greater top-down pressure from natural enemies.

Climate Change and Tritrophic Interactions: Will Modifications to Greenhouse Gas Emissions Increase the Vulnerability of Herbivorous Insects to Natural Enemies?

“…Holton et al (2003) found that elevated CO 2 concentrations had no impact on the performance of Compsilura concinnata (Meigen). Similarly, the mortality of different leafminer species associated with parasitism under elevated CO 2 was not significantly different from that observed under ambient CO 2 conditions (Stiling et al 1999). All of these cited studies demonstrate the major variability in parasitoid performance under elevated CO 2 conditions.…”

Climate change and its effects on terrestrial insects and herbivory patterns

“…The expected concentration of CO 2 in the year of 2100 ranges from 540 to 970 ppm compared to about 280 ppm in the pre-industrial era (Stiling et al 1999), and changes in plant quality due to elevated CO 2 may affect herbivory patterns and insect richness, abundance and/ or diversity. Many studies have now addressed effects of CO 2 enrichment on herbivores mediated by changes in host plant characteristics and how herbivores respond to these altered conditions (reviewed by Stiling & Cornelissen 2007).…”

Nitrogen inputs and losses in response to chronic CO<sub>2</sub> exposure in a subtropical oak woodland

“…We estimated G. elliottii annual aboveground production as the annual flux of G. elliottii mass collected in litter traps (Stiling et al, 1999(Stiling et al, , 2002(Stiling et al, , 2009). Litter of G. elliottii was sorted and measured separately beginning in 1999; in 1997 and 1998, G. elliottii litter fall was measured together with other "non-oak" species.…”

“…From 2000 to 2006, litter of the oaks and of G. elliottii was scored for damage by insect herbivores and sorted, counted, and weighed separately by species and insect damage category as described previously (Stiling et al, 1999(Stiling et al, , 2009. The rate of litterfall of herbivore-damaged leaves, L (g m −2 year −1 ), was determined for each species as the total mass of damaged litter divided by the area of the litter traps in each chamber.…”