Effects of Elevated CO and O on Aboveground Brassicaceous Plant-Insect Interactions.

Atmospheric gases, such as carbon dioxide (CO) and ozone (O), influence plant-insect interactions, with variable effects. The few studies that have investigated the direct effects of elevated CO (eCO; 750-900 ppm) or elevated O (eO; 60-200 ppb) on insects have shown mixed results. Instead, most research has focused on the indirect effects through changes in the host plant. In general, the lower nitrogen levels in C3 brassicaceous plants grown at eCO negatively affect insects and may result in compensatory feeding. Phytohormones involved in plant resistance may be altered by eCO or eO. For example, stress-related jasmonate levels, which lead to induced resistance against chewing herbivores, are weakened at eCO. In general, eCO does not affect herbivore-induced plant volatiles, which remain attractive to natural enemies. However, floral volatiles and herbivore-induced plant volatiles may be degraded by O, affecting pollination and foraging natural enemy behavior. Thus, eCO and eO alter plant-insect interactions; however, many aspects remain poorly understood.