PARENT SESSION
Oral Session #78: Insect Population and Community Ecology. Presiding: R. Denno.
Friday, August 10, 2001. 8:00 AM to 11:45 AM. Hall of Ideas I.

Aphid individual, population and natural enemy responses to elevated CO₂ or O₃.

Awmack, Caroline¹, Harrington, Richard², Lindroth, Richard ¹, ^{1 2}

ABSTRACT- Although the effects of CO₂ and O₃ on the performance of individual insects are increasingly well understood, little is known about the implications of a parallel increase in these two pollutants on insect populations. At the Aspen FACE (Free-Air CO₂ Enrichment) site, semi-natural ecosystems are fumigated with elevated atmospheric CO₂ or O₃ to simulate the impacts of climate change on the growth and development of a northern deciduous forest ecosystem. We measured individual fitness parameters (MRGR, development time, adult weight, potential and achieved fecundity) of the birch-feeding aphid Cepegillettea betulaefoliae and the growth of aphid populations protected from natural enemies with mesh bags. We compared these data with unmanipulated populations of aphids and natural enemies on the trees. Individual measures of fitness did not predict population responses. Aphid populations were unaffected by elevated CO₂ and increased by 80% at elevated O₃ while CO₂ negated the positive effect of elevated O₃. There was a strong correlation between populations of aphids protected by mesh bags and the unprotected aphid populations on the trees. As elevated CO₂ and O₃ had little effect on natural enemy numbers we suggest that bottom-up effects mediated by changes in plant quality may be more important than top-down effects in this system.

KEY WORDS: aphids, natural enemies, co₂, o₃