How does atmospheric elevated CO2 affect crop pests and their natural enemies? Case histories from China

Global atmospheric CO2 concentrations have risen rapidly since the Industrial Revolution and are considered as a primary factor in climate change. The effects of elevated CO2 on herbivore insects were found to be primarily through the CO2-induced changes occurring in their host plants, which then possibly affect the intensity and frequency of pest outbreaks on crops. This paper reviews several ongoing research models using primary pests of crops (cotton bollworm, whitefly, aphids) and their natural enemies (ladybeetles, parasitoids) in China to examine insect responses to elevated CO2. It is generally indicated that elevated CO2 prolonged the development of cotton bollworm, Helicoverpa armigera, a chewing insect, by decreasing the foliar nitrogen of host plants. In contrast, the phloem-sucking aphid and whitefly insects had species-specific responses to elevated CO2 because of complex interactions that occur in the phloem sieve elements of plants. Some aphid species, such as cotton aphid, Aphis gossypii and wheat aphid, Sitobion avenae, were considered to represent the only feeding guild to respond positively to elevated CO2 conditions. Although whitefly, Bemisia tabaci, a major vector of Tomato yellow leaf curl virus, had neutral response to elevated CO2, the plants became less vulnerable to the virus infection under elevated CO2. The predator and parasitoid response to elevated CO2 were frequently idiosyncratic. These documents from Chinese scientists suggested that elevated CO2 initially affects the crop plant and then cascades to a higher trophic level through the food chain to encompass herbivores (pests), their natural enemies, pathogens and underground nematodes, which disrupt the natural balance observed previously in agricultural ecosystems.