Sublethal effects of abamectin on Phthorimaea operculella (Zeller) (Lep.: Gelechiidae) under laboratory conditions

The sublethal effects of abamectin was investigated on stable population growth parameters of Phthorimaea operculella at 26 ± 1ºC, 65 ± 5% RH and photoperiod of 16:8 h (L: D). Four hundred one-day- old eggs of the pest were dipped in abamectin LC30. Then they transferred to Petri dishes. Distilled water was used as control treatment. After eggs hatched, the first instar larva were transferred on potato tubers and placed in clear plastic dishes (4×8 cm) until adults emerged. A total 40 and 80 first instar larvae were used in the treatment and control, respectively. After emergence, males and females were paired in the plastic dishes and fecundity of females was recorded daily. Carey’s procedure was used to estimate the population growth parameters. In control and insecticide treatment, net reproductive rates (R0) intrinsic rates of increase (rm) doubling times (DT) gross reproductive rate (GRR) finite rates of increase () and mean generation times )T) were estimated to be 3.72 ± 0.58, 2.09 ± 0.048 female/female/generation and 0.06 ± 0.007 , 0.03 ± 0.0008 female/female/days and 48.08 ± 7.6, 20.52 ± 0.43 female/female/generation, 10.97 ± 2.22 , 8.12 ± 1.36 days and 22.30 ± 4.16, 24.02 ± 0.034 day and 1.062 ± 0.16, 1.034 ± 0.0008 female/female/day, respectively. Statistical analyses showed that abamectin had significantly adverse effects on stable population growth parameters of P. operculella, So that it caused reduction in intrinsic rate of increase (rm) up to 50% in comparison with the control.