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Abstract
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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
LC50 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 LC30 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
LC30 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.
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