Climate change: Resetting plant-insect interactions

Abstract

Elevated CO 2 and temperature are altering the interactions between plants and insects with important implications for food security and natural ecosystems. Ecologically, the acceleration of plant phenology by warming is generating mismatches between plants and insect pollinators. Similarly, shifting the rate of plant development relative to insect development can amplify or minimize the consequences of herbivory. Warming also enables some insects to increase the number of generations per year, thus increasing damage to plant communities. The suitability of plant tissues as food for insects also is modulated by global change. Elevated CO 2 typically increases the concentration of leaf carbohydrates and in combination with elevated temperature decreases nitrogen content. Together, these changes lower nutritional value, causing herbivores to consume more foliage to meet their nutritional needs. While the responses of primary metabolites in plants to global change are reasonably well understood, how elevated CO 2 and temperature affect plant defensive compounds (allelochemicals) is considerably less predictable. Recent studies indicate that exposure to elevated CO 2 suppresses the plant defense hormone jasmonic acid (JA) while stimulating production of salicylic acid (SA). By differentially affecting defense compounds, these changes in plant hormones potentially increase susceptibility to chewing insects and enhance resistance to pathogens. Exposure to elevated temperature, in contrast, stimulates JA, ethylene, and SA, enhancing defenses. A deeper understanding of how elevated CO 2 and temperature, singly and in combination, modulate plant hormones promises to increase our understanding of how these elements of global change will affect the positive and negative interactions between plants and insects.