Effects of six recommended pesticides in rice fields on fecundity and survival of predator Andrallus spinidens under laboratory conditions

The predatory bug, Andrallus spinidens (F.) is one of the most important biological control agents of lepidopteran pests in rice fields of Iran. An experiment was conducted to evaluate the effects of six recommendedpesticides (including 3 insecticides, 2 fungicides and 1 herbicide) on A. spinidens thorough a completely randomized design (CRD) replicated 6 times. The ingestion method was performed on the 4th–instar nymphs of the predator. Pesticides concentration were prepared based on the field recommended doses. Distilled water was used as the control. Newly emerged 4th instar nymphs provided with 2–ml of pesticides inside small containers for 24 hours. Thereafter, the survived nymphs were provided with distilled water and 2–3 last instar larvae of Galleria mellonella. The experiments were carried out under laboratory conditions at 25±0.5 °C, 70±5% RH and a photoperiod of 16:8 h (L: D). Mortality was recorded daily until the adult emergence. The results revealed that maximum reduction in fecundity of A. spinidens occurred in Fipronil, Diazinon and Malathion treatments and the minimum reduction was observed in Pretilachlor treatment compared with that of control. Based on the total effect of IOBC classification, Fipronil, Diazinon and Malathion insecticides with 100% mortality were placed in the class 4 (harmful). Similarly, E+C and Tricyclazol fungicides were grouped in class 3 (Moderately harmful) with 86.84% and 91.58% total effect, respectively. Pretilachlor herbicide, with 74.39% mortality was placed in category 2 (slightly offensive). Therefore, if field results are confirmed, studied insecticides are not suitable candidates for integrated pest management programs in rice when the predator is active.