Lethal and sublethal effects of abamectin and deltamethrin on potato tuber moth, Phthorimaea operculella (Lepidoptera: Gelechiidae)

The potato tuber moth (PTM), Phthorimaea operculella (Zeller) is one of the important pests of potato in tropical regions. In this research, the toxicity of two insecticides, abamectin and deltamethrin on P. operculella was studied at 26 ± 1 C°, 65 ± 5% RH and photoperiod of 16:8 h (L: D). The concentrations were determined by preliminary dose setting experiments. Distilled water was used as control. LC₅₀ values for egg, first instar larvae and adult stages in abamectin were 0.92, 0.014 and 0.46 mg ai/l and in deltamethrin were 0.09, 0.024 and 0.29 mg ai/l, respectively. The sublethal effects of abamectin and deltamethrin on population growth parameters of P. operculella were determined at mentioned conditions. Four hundred 1 day old eggs of the pest were dipped in insecticides solutions (LC₃₀). After egg hatching, the first instar larvae were transferred on potato tubers and placed in transparent plastic dishes. After adults' emergence, 20 females were used for each treatment in life table experiments. In control, abamectin and deltamethrin treatments intrinsic rates of increase were estimated to be 0.060, 0.042 and 0.141 day^-1, respectively. Statistical analyses showed that deltamethrin had the higher toxicity to egg and adult stages of PTM and abamectin had the higher toxicity to its first instar larvae. Since deltamethrin increased the stable population parameters of P. operculella specially its intrinsic rate of increase, thus it might not be recommended for control of PTM. However based on lethal and sublethal effects, abamectin could be suitable for management of this pest.