Sublethal effects of imidacloprid and pymetrozine on population growth parameters of cabbage aphid, Brevicoryne brassicae on rapeseed, Brassica napus L.

Efficiency of imidacloprid and pymetrozine on population growth parameters of cabbage aphid, Brevicoryne brassicae L. (Homoptera: Aphididae) was determined using demographic toxicology by leaf dip method. At first, bioassay tests were performed. The LC50 value and confidence limit for imidacloprid and pymetrozine were 1.61 x 10(-5) mol/L (0.74 x 10(-5)-2.66 x 10(-5)) and 2.14 x 10(-4) mol/L (1.24 x 10(-4)-3.40 x 10(-4)), respectively. To evaluate the sublethal effect of two insecticides on population growth parameters of cabbage aphid, LC30 concentrations of imidacloprid and pymetrozine were used at 5 mol/L and 30 mol/L. The experiments were carried out in a incubator at 20 +/- 1 degrees C, 60% +/- 5% RH and 16: 8 (L: D) photoperiod on canola seedlings, Brassica napus L. var. 'PF'. Net fecundity rate decreased in both insecticide-treated populations. Intrinsic rates of increase (r(m)) were lower in imidacloprid and pymetrozine treatments than in controls. Intrinsic birth rates also decreased in treated populations. There was a relative increase in intrinsic death rates of treated populations. The mean generation times and doubling time were also lower in populations treated with insecticides than in controls. There was a considerable reduction in the average numbers of nymphs reproduced per female as compared with the control. The average longevity of female adults in the control was significantly different from those treated with imidacloprid and pymetrozine. However, there was no significant differences in aphid life-table parameters between the two insecticide-treated populations (P > 0.01).