Host-selection behavior and physiological mechanisms of the cotton aphid, Aphis gossypii, in response to rising atmospheric carbon dioxide levels

Rising atmospheric carbon dioxide (CO2) levels can markedly affect the growth, development, reproduction and behavior of herbivorous insects, mainly by changing the primary and secondary metabolites of their host plants. However, little is known about the host-selection behavior and the respective intrinsic mechanism of sap-sucking insects in response to elevated CO2. In this experiment, the host-selection behavior, as well as the physiological mechanism based on the analysis of growth, development and energy substances, and the expression of the olfactory-related genes of the cotton aphid, Aphis gossypii, were studied under ambient (407.0 +/- 4.3 mu l/L) and elevated (810.5 +/- 7.2 mu l/L) CO2. The results indicated that the aphids reared under ambient and elevated CO2 did not differ in their level of preference for cotton seedlings, whatever the CO2 conditions in which the plants developed. However, aphids reared under elevated CO2 showed a greater ability to respond to the plant volatiles compared to aphids that developed under ambient CO2 (+ 23.3%). This suggests that rising atmospheric CO2 enhances the activity of host selection in this aphid. Compared with ambient CO2, elevated CO2 significantly increased aphid body weight (+ 36.7%) and the contents of glycogen (+ 18.9%), body fat (+ 14.6%), and amino acids (+ 16.8%) and increased the expression of odor-binding protein genes, OBP2 (+ 299.6%) and OBP7 (+ 47.4%), and chemosensory protein genes, CSP4 (+ 265.3%) and CSP6 (+ 50.9%), potentially enhancing the overall life activities and upregulating the olfactory ability of A. gossypii. We speculated that the rising atmospheric CO2 level would likely aggravate the damage caused by A. gossypii due to the higher potential host selection and increased general activity under future climate change.