Impacts and responses at population level of herbivorous insects to elevated CO2

Most studies of responses of insects to elevated carbon dioxide have been m ade using short-term exposures to treated food plants and have involved mea surements of responses in growth, reproduction, food consumption and effici encies of conversion at specific stages in the life cycle. These will be re viewed in the light of longer-term studies recently published where whole g enerations have been reared in chambers with simultaneous treatment of plan ts and where insects have been free to select their food and microenvironme nt. Factors such as seasonal change in plants, choice of food plant, mode o f feeding, timing of exposure, temperature, the role of natural enemies are considered and the whole placed in the context of other aspects of climate change. It is concluded that in studies to date, the only feeding guild in which so me species have shown increases in population density in elevated carbon di oxide are the phloem feeders. Chewing insects (both free-living,and mining) generally have shown no change or reduction in abundance, though relative abundance may be greatly affected. Compensatory feeding is common in these groups.