High CO2—a gourmet boon for crop pest

Increases in atmospheric carbon dioxide could weaken soybean defenses—and be the best news Japanese beetles have had in a long time.

Two new papers suggest that the higher CO2 concentrations predicted for 2050 will mean extra trouble for farmers fighting insect pests, says Evan H. DeLucia of the University of Illinois at Urbana–Champaign (UIUC). The research was inspired by experiments at the SoyFACE facility on the UIUC campus, where researchers are boosting CO2 concentrations in soybean plots to mimic future atmospheres.

Researchers noticed that the plots with CO2 pumped up to 550 parts per million (ppm) were particularly popular with Japanese beetles, which briskly chew soybean leaves into tatters. DeLucia and his colleagues tested beetle diets in the lab. Eating leaves from soybean plants grown in the 550 ppm CO2 prolonged the beetles’ life spans by up to 25 percent. Female beetles living off those leaves laid twice as many eggs as moms eating regular soybean leaves, the team reports in the April Environmental Entomology.

The beetle bonanza seems to occur because the extra CO2 impairs the soybean’s normal defenses against ravening insects. Like many plants, a soybean that gets bitten by a bug produces a surge of defensive chemicals that jam an insect’s digestive enzymes. Under high CO2 concentrations, the genes controlling that surge weren’t as active, the research team reports in the April 1 Proceedings of the National Academy of Sciences.