In our Editorial of 15 April 2000 -- Biodiversity and CO2 -- we suggest that "the elevated levels of primary production that elevated levels of CO2 induce in earth's plants provide the basis for greater populations of herbivores." That this indeed is likely to be the case is further suggested by the review of plant-animal interactions in 51 terrestrial ecosystems conducted by McNaughton et al. (1989), who determined that the biomass of terrestrial herbivores is a strongly increasing function of aboveground primary production. It is also supported by the review of Cyr and Pace (1993), who found that the herbivore biomass of aquatic habitats likewise increases in response to increases in marine and freshwater vegetative productivity.
Clearly, however, not all herbivores will fare equally well in a CO2-enriched world, and there could well be some losers among the many winners. Hence, this field of science is beginning to garner greater and greater attention. In fact, fully 26 atmospheric CO2 enrichment studies on aphids alone had been conducted at the time of the review of Holopainen (2002), who found their performance to be increased in six studies, decreased in six others, and unaffected in the remaining 14 studies, for an overall nil response. This result is encouraging, for it suggests that outbreaks of this important insect pest will not be promoted in a CO2-enriched and, therefore, greener world of the future.
In an earlier review that dealt with several types of herbivorous insects, Whittaker (1999) had found a slight increase in the activity of phloem-feeding aphids in CO2-enriched air; but either no change or actual reductions in the abundance of chewing insects. Overall, therefore, we can probably expect little change, or possibly even a slight decrease, in the fraction of agricultural crop production that is typically destroyed by herbivorous insects as the air's CO2 content continues to rise.
References
Cyr, H. and Pace, M.L. 1993. Magnitude and patterns of herbivory in aquatic and terrestrial ecosystems. Nature 361: 148-150.
Holopainen, J.K. 2002. Aphid response to elevated ozone and CO2. Entomologia Experimentalis et Applicata 104: 137-142.
McNaughton, S.J., Oesterheld, M., Frank, D.A. and Williams, K.J. 1989. Ecosystem-level patterns of primary productivity and herbivory in terrestrial habitats. Nature 341: 142-144.
Whittaker, J.B. 1999. Impacts and responses at population level of herbivorous insects to elevated CO2. European Journal of Entomology 96: 149-156.