LAUSR

Increasing atmospheric CO2 concentrations affect the performances of herbivores. Most previous studies have focused on the effects of abrupt increases in CO2 concentration on herbivore performance, but knowledge about the response of herbivores to gradual increases in CO2 is lacking. We tested the hypothesis that herbivores will show different responses to abrupt and gradual CO2 increases. We measured the performance of the brown planthopper (BPH) (Nilaparvata lugens (Stål)) reared on rice for 15 successive generations under three CO2 levels: ambient CO2 (375 µl/L), a gradual increase in CO2 (25 µl/L increase per generation, 390–750 µl/L), and an abrupt increase in CO2 (750 µl/L). During the first generation, the female and male longevities were affected by both the gradual and abrupt increases in CO2, and the fecundity and net reproductive rate (R0) of the BPH in the abruptly increased CO2 treatment were significantly lower than those in the other two treatments; there were no significant differences in the intrinsic rate of increase (r) and the finite rate of increase (λ) among the three CO2 treatments. After 14 generations, female longevity was significantly prolonged in treatments with both gradual and abrupt CO2 increases. The fecundity of the BPHs reared in the gradual CO2 treatment was significantly higher than that in the other two CO2 treatments. According to the population parameters (r, λ, and R0) and population projection, under a gradual increase in CO2, the BPH population size was higher than that under an abrupt CO2 increase. We concluded that the BPH abundance will increase under a gradual CO2 increase and consequently result in an increase in rice yield loss.