Influence of elevated CO2, nitrogen, and Pinus elliottii genotypes on performance of the redheaded pine sawfly, Neodiprion lecontei
Slash pine (Pinus elliottii Engelm. var. elliottii) seedlings were grown in open-top chambers receiving ambient or elevated atmospheric CO2 (-365 or -720 muL.L-1). Seedlings received low or high soil nitrogen treatments (0.02 or 0.2 mg N.g(-1)) 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 larvae of the redheaded pine sawfly (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 on the basis of CO2 or N but were higher in needles from the resistant family. Alterations in needle chemistry were associated with variations in sawfly growth and development. Larvae performed most poorly on the family most resistant to fusiform rust, suggesting that 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 or resistant needles or needles from low-N fertilization 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 redheaded pine sawfly could suffer as the level of atmospheric CO2 continues to rise.