Increased levels of atmospheric carbon dioxide (CO2) are likely to affect the trophic relationships that exist between plants, their herbivores, and the herbivores’ natural enemies. We examined interactions across three trophic levels, a transgenic Bacillus thuringiensis Berliner cotton, an aphid herbivore (Aphis gossypii Glover), and a coccinellid predator (Leis axyridis Pallas) as affected by elevated CO2 concentrations. Experimental CO2 levels included ambient and 2× and 3× ambient CO2 levels. Plant height, biomass, leaf area, and carbon:nitrogen (C:N) ratios were significantly higher in plants exposed to elevated CO2 levels compared with that in plants exposed to ambient CO2. More dry matter and fat content and less soluble protein were found in A. gossypii in elevated CO2 treatments. Cotton aphid fecundity significantly increased with increased CO2 concentrations. The aphid fecundity significantly increased through successive generations reared on plants grown under elevated CO2, suggesting that the changes in plant quality resulting from elevated CO2 altered aphid quality as prey for L. axyridis through the food chain. Significantly higher mean relative growth rates were observed in lady beetle larvae under elevated CO2 treatments. Also, the larval and pupal durations of the lady beetle were significantly shorter and aphid consumption rates increased when fed A. gossypii from elevated CO2 treatments. Our data showed that increasing CO2 concentrations could alter the preference of lady beetle to aphid prey and enhance the biological control of aphids by lady beetle. This study provides the first empirical evidence that changes in prey reared on host plants grown at different levels of CO2 can alter the feeding preference of their natural enemies.
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