Effects of elevated CO₂ and temperature‐grown red and sugar maple on gypsy moth performance

Abstract

Summary Few studies have investigated how tree species grown under elevated CO 2 and elevated temperature alter the performance of leaf‐feeding insects. The indirect effects of an elevated CO 2 concentration and temperature on leaf phytochemistry, along with potential direct effects on insect growth and consumption, may independently or interactively affect insects. To investigate this, we bagged larvae of the gypsy moth on leaves of red and sugar maple growing in open‐top chambers in four CO 2 /temperature treatment combinations: (i) ambient temperature, ambient CO 2 ; (ii) ambient temperature, elevated CO 2 (+ 300 μL L −1 CO 2 ); (iii) elevated temperature (+ 3.5°C), ambient CO 2 ; and (iv) elevated temperature, elevated CO 2 . For both tree species, leaves grown at elevated CO 2 concentration were significantly reduced in leaf nitrogen concentration and increased in C: N ratio, while neither temperature nor its interaction with CO 2 concentration had any effect. Depending on the tree species, leaf water content declined (red maple) and carbon‐based phenolics increased (sugar maple) on plants grown in an enriched CO 2 atmosphere. The only observed effect of elevated temperature on leaf phytochemistry was a reduction in leaf water content of sugar maple leaves. Gypsy moth larval responses were dependent on tree species. Larvae feeding on elevated CO 2 ‐grown red maple leaves had reduced growth, while temperature had no effect on the growth or consumption of larvae. No significant effects of either temperature or CO 2 concentration were observed for larvae feeding on sugar maple leaves. Our data demonstrate strong effects of CO 2 enrichment on leaf phytochemical constituents important to folivorous insects, while an elevated temperature largely has little effect. We conclude that alterations in leaf chemistry due to an elevated CO 2 atmosphere are more important in this plant–folivorous insect system than either the direct short‐term effects of temperature on insect performance or its indirect effects on leaf chemistry.