|Saxon, Milam - AUBURN UNIVERSITY|
|Davis, Micheal - UNIV.OF SOUTHERN MISS.|
|Pritchard, Seth - BELMONT UNIVERSITY|
|Stelzer, Hank - UNIV. OF MISSOURI|
|Rogers Jr, Hugo|
|Dute, Roland - AUBURN UNIVERSITY|
Submitted to: Canadian Journal of Forest Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 18, 2003
Publication Date: May 10, 2004
Citation: Saxon, M.E., Davis, M.A., Pritchard, S.G., Runion, G.B., Prior, S.A., Stelzer, H.E., Rogers Jr, H.H., Dute, R.R. 2004. Influence of elevated co2, nitrogen, and pinus elliottii genotypes on performance of red-headed pine sawfly, neodiprion lecontei. Canadian Journal of Forest Research. 34(5):1007-1017. Interpretive Summary: The level of carbon dioxide (CO2), a by-product of burning fossil fuels like gasoline and coal, continues to rise in the atmosphere. Plants, which absorb CO2 for photosynthesis, may be affected by these higher levels, subtly changing the chemical composition of their leaves, for instance. Insects that have a plant diet could, therefore, also be affected by plant changes in high CO2. In our study, red-headed pine sawflies consumed slash pine needles grown in high or normal, present-day CO2 levels. The larvae consuming high CO2-grown needles grew more slowly and took longer to form their cocoons than those fed needles from regular CO2. The performance of this insect could decline in a future high CO2 environment.
Technical Abstract: Slash pine (Pinus elliottii var. elliottii Engelm.) seedlings were grown in open-top chambers receiving ambient or elevated atmospheric CO2 (365 ppm and 720 ppm). Seedlings received low or high soil nitrogen treatments (0.02 or 0.2 mg N/g) and represented three families varying in resistance to fusiform rust, Cronartium quercuum (Berk.) Miyabe ex Shirai f. sp. fusiforme (Hedgc. & N. Hunt) Burdsall & G. Snow. Following 18 months of exposure to treatment conditions, current year needles were fed to red-headed pine sawfly larvae (Neodiprion lecontei Fitch). Needle N concentration and water content were lower in elevated CO2 and in low N treatments. Total phenolics increased under high CO2 and low N conditions, and were highest in the resistant family. Condensed tannins did not vary based on CO2 or N, but were higher in needles from the resistant family. Alterations in needle chemistry affected sawfly growth and development. Larvae performed most poorly on the family most resistant to fusiform rust, suggesting the mechanism for resistance was similar in both cases. Relative consumption rates increased with CO2-enriched needle diets but were depressed for resistant needles, suggesting deterrence from the higher total phenolics in this family. Diets using CO2-enriched needles, resistant needles, or needles from low N fertility treatments resulted in lower relative growth rates for the larvae. Days to pupation increased for larvae fed CO2-enriched and low N needles. These results suggest that the red-headed pine sawfly could suffer as atmospheric CO2 continues to rise.