Loblolly pine grown under elevated CO₂ affects early instar pine sawfly performance.

Area of Science:

• Forest Ecology
• Insect-Plant Interactions
• Climate Change Biology

Background:

• Loblolly pine (Pinus taeda) is a key timber species facing changing atmospheric conditions.
• Red-headed pine sawfly (Neodiprion lecontei) is a significant herbivore of loblolly pine.
• Elevated atmospheric carbon dioxide (CO2) can alter plant physiology and nutritional quality.

Purpose of the Study:

• To investigate the impact of elevated CO2 on loblolly pine needle quality.
• To assess the performance of Neodiprion lecontei larvae feeding on needles from trees grown under different CO2 regimes.
• To understand the implications for forest pest dynamics under future climate scenarios.

Main Methods:

• Loblolly pine seedlings were grown in open-topped chambers under ambient and elevated CO2 concentrations (150 and 300 μl l−1 above ambient).
• Needles were subjected to 96-hour feeding trials with second-instar Neodiprion lecontei larvae.
• Leaf nitrogen, starch content, starch:nitrogen ratio, and key monoterpenes were analyzed.
• Larval consumption rates, relative growth rates, and nitrogen accumulation were measured.

Main Results:

• Larval consumption rate significantly increased with elevated CO2, with 21% higher consumption in the highest CO2 regime.
• Elevated CO2 led to decreased leaf nitrogen and increased leaf starch, raising the starch:nitrogen ratio.
• Larval growth rates were not significantly different across CO2 treatments.
• Nitrogen utilization efficiency increased, maintaining nitrogen accumulation rates despite lower nitrogen consumption.

Conclusions:

• Changes in pine needle quality under elevated CO2, specifically increased starch and decreased nitrogen, drive increased sawfly consumption.
• Despite altered food quality, Neodiprion lecontei larvae demonstrate compensatory mechanisms (increased nitrogen utilization efficiency) that maintain growth rates.
• Young sawfly larvae may not be severely impacted by projected changes in needle quality, indicating potential resilience of this forest pest to climate change.