Sublethal effects of malathion on biological traits and life table parameters of the soybean aphid, Aphis glycines (Matsumura)

The soybean aphid, Aphis glycines is one of the most devastating pests on soybean worldwide. Current management of A.glycines relies on insecticides application. The application of malathion has been proposed as an effective strategy to control A.glycines in soybean field. Malathion not only kills A.glycines at lethal concentration, but also causes various physiological and behavioral changes at sublethal concentration. The effects of three sublethal concentrations of malathion on the biological traits and demographic parameters of A.glycines were investigated. After being exposed to 0.20 mg/L malathion, the duration of nymph of A.glycines was significantly longer (7.48 d±0.18 d) than that of the control (5.78 d±0.30 d); and the reproductive period, adult longevity and duration of whole life of A.glycines decreased significantly, which were 4 d, 6 d and 4 d less than those of the control, respectively. Low concentration (0.10 mg/L) of malathion could stimulate the fecundity, and the total nymphs produced by single aphid increased 24% comparing with that of the control. However, high concentration (0.20 mg/L) of malathion inhibited the fecundity, and the total nymphs produced by single aphid decreased 37% as compared with that of the control. The demographic growth parameters, such as the net reproductive rate (R0), the intrinsic rate of increase (rm), and finite rate of increase (λ) of A.glycines were significantly lower in the treatment with 0.20 mg/L malathion than those of the control, but the population doubling time (Dt) was significantly longer than that of the control. However, the change of the parameters of A.glycines under 0.10 mg/L malathion treatment was opposite to that of 0.20 mg/L malathion treatment. No significant difference of parameters between 0.05 mg/L treatment and control was observed.