To examine how the major elements of global change affect herbivory in agroecosystems, a multi-factorial experiment was conducted in which soybeans were grown at two levels of carbon dioxide and temperature, including those predicted for 2050, under otherwise normal field conditions. Japanese beetles (Popilla japonica Newman) were enclosed on foliage for 24 hours, after which the beetle survivorship, total and per capita leaf consumption, and leaf protease inhibitor activity was measured. The direct effect of temperature on beetle consumption and survivorship was also measured under controlled environmental conditions. No differences in total foliage consumption were observed; however, beetles forced to feed at elevated temperature in the field demonstrated greater per capita consumption and reduced survivorship compared to beetles feeding at ambient temperature. Survivorship was also greater for beetles that consumed foliage grown under elevated CO2, but there were no interactive effects of CO2 and temperature, and no differences in leaf chemistry were resolved. Leaf consumption by beetles increased strongly with increasing temperature up to ~37° C, above which increased mortality caused a precipitous decrease in consumption. An empirical model based on the temperature dependence of leaf consumption and flight suggests that a 3.5° C increase in temperature will increase the optimal feeding window for the Japanese beetle by 290%. Elevated temperature and CO2 operating independently have the potential to greatly increase foliage damage to soybean by chewing insects, such as Popillia japonica potentially affecting crop yields.
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Impact of elevated carbon dioxide and increased temperature on Japanese beetle herbivory
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