Print PageMany studies have shown that an increase in anthropogenic CO2 increases plant productivity. However, for some plant species elevated CO2 decreases defenses, thereby increasing susceptibility to herbivory. Increased temperature is known to increase insect metabolic rate. This research examines the interactions of a highly invasive herbivore insect (Popillia japonica), with a model agricultural crop (Glycine max) and climate conditions predicted for 2050. These conditions—namely increased temperature in combination with CO2—are expected to result in higher Japanese Beetle damage.
A multi-factorial experiment was conducted where soybeans were grown at two levels of CO2 and temperature at the SoyFACE research facility. Soybeans were subject to 24 hours of Japanese beetle feeding, after which the accumulation of leaf protease inhibitor and beetle consumption were measured from collected leaf tissue. Additional experiments examined the impact of temperature on beetle consumption at eight different temperatures. These results were used to model how climate conditions resembling 2050 will affect large-scale beetle herbivory in the Midwest.
Results/Conclusions
Our experiments revealed that beetle consumption rate increases linearly by 1% per degree until 37oC. Past this point, beetle mortality causes a decrease in feeding. In the field experiment, plants exposed to elevated temperature and ambient CO2 obtained 3% more damage. The expected rise in consumption caused by decreased plant defenses in plants exposed to elevated CO2 was dampened slightly by the counteracting increase in defenses caused by elevated temperature.
Our empirical model indicated that a 3.5 oC increase in temperature by 2050 would increase the feeding duration of Japanese Beetles by up to 40% during summer. Data indicate that, within ideal feeding temperatures, herbivory rate increases by 3%. As little as 20% leaf damage before seed fill will decrease yield by 15%, resulting in up to $670 million in damage.
