Effects of Diazinon and Fipronil on Different Developmental Stages of Trichogramma brassicae Bezdenko (Hym.; Trichogrammatidae)
The integration of biological and chemical control approaches is very important for a successful Integrated Pest Management (IPM) program. Demographic approaches give a better understanding of the side effects of pesticides on beneficial organisms. In this study, laboratory bioassays were set up to evaluate the lethal and sublethal effects of diazinon and fipronil on different stages of Trichogramma brassicae Bezdenko (Hymenoptera: Trichogrammatidae). The effects of Field Recommended Concentration (FRC) of diazinon and fipronil were studied on larvae, prepupa and pupae of the parasitoid. Diazinon and fipronil reduced adult emergence by 99.74 and 50.46%, respectively. The LC 50 values for diazinon and fipronil on adult stage were 0.11 and 0.46 µg ai ml -1 , respectively. The sublethal effects of the chemicals were studied on life-table parameters of the parasitoid emerging from parasitized eggs exposed to the FRC of the insecticides at larval stage and also adults exposed to LC 30 of the insecticides. Longevity and progeny production were affected by the insecticides in comparison to the control. Three main lifetable parameters including intrinsic rate of increase ( rm), Doubling Time (DT) and net Reproduction rate ( R0) were negatively affected by the sublethal treatments. The intrinsic rate of increase for control, diazinon and fipronil exposed populations at larval stage were 0.28, 0.23 and 0.12, respectively and were 0.26, 0.04 and 0.08 for populations exposed to LC 30 at adult stage, respectively. The sex ratio of offspring at all insecticide treatments has led to the production of female offspring by the chemicals. These findings showed that diazinon and fipronil were harmful for T. brassicae , thus semifield and field studies are suggested for getting more applicable results for possibly using them in IPM programs.