Plant-Insect-Parasitoid Responses to elevated C02

Predicted increases in atmospheric CO 2 levels may alter important plant-insect-parasitoid associations due to the indirect effects of CO 2 enrichment on phytochemicals important for herbivore and parasitoid nutrition. We will follow CO 2 -induced changes in leaf chemistry of three hardwood tree species, consequent effects on a leaf feeding lepidopteran generalist, and the direct and indirect host-mediated impacts on the third trophic level, an endoparasitoid of the herbivore larvae. The outcomes of the project will enhance our predictability of how the forecast atmospheric CO 2 enrichment may increase the risks of gypsy moth outbreaks due to altered host tree- insect-parasitoid interactions. The proposed study will be conducted within the Swiss Canopy Crane Project in a full-size natural mixed-species forest at the web-FACE study site near Basel, Switzerland. We will investigate the effects of CO 2 on the interaction between gypsy moth (Lymantria dispar L.) larvae and mature oak (Quercus petraea), beech (Fagus sylvatica) and hornbeam (Carpinus betulus) trees by bagging larvae from second instar within the canopy at (1) ambient CO 2 (370 520 l l -1 ) and (2) elevated CO 2 (520 l l -1 ). Larvae will be reared to pupation in the tree canopy and leaf samples will be taken biweekly to determine levels of total nitrogen, carbon, water, fiber, non- structural carbohydrates, fatty acids and an estimate of phenolic defensive compounds (condensed and hydrolyzable tannins, protein precipitating ability) in the tree foliage. Effects of elevated CO 2 on the third trophic level will be studied by keeping bagged gypsy moth larvae previously parasitized by the braconid wasp Glyptapanteles liparidis in the tree canopy until the parasitoids emerge from their host. Gypsy moth and parasitoid growth and development parameters will be recorded. A second set of experiments will be done under laboratory conditions: both unparasitized and parasitized gypsy moth larvae will be fed with leaf powder diet made from lyophilized foliage of either oak, beech or hornbeam grown under ambient and elevated CO 2 levels, respectively. Growth, consumption, and utilization patterns of the larvae on the different diets will be recorded. In the parasitization experiment, we will follow parasitoid development success, wasp sex ratio, weight, and longevity. In a parasitization choice experiment with preconditioned larvae feeding leaf powder diets from either ambient or elevated CO 2 foliage, we will demonstrate if female wasps are able to develop oviposition strategies for low- quality and high-quality hosts.