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Abstract
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Trichogramma is an important genus of egg parasitoids that is
frequently used as biological control agents against lepidopteran pests. The
most widespread species of Trichogramma in Iran is Trichogramma
brassicae Bezdenko that is widely used against rice stem borrer, Chilo
suppressalis (Walker). In this study, the sublethal effects of LC30
concentration of diazinon and fipronil were studied on the functional
response of T. brassicae to different densities (2, 4, 8, 16, 32 and 64) of
Sitotroga cerealella (Olivier) eggs. The experiment was carried out in an
insectarium at 25 ± 1 ºC, 70 ± 10% RH, and a photoperiod of 16: 8 (L: D)
h. Young adult females of the parasitoid were exposed to LC30 of either
insecticides for an appropriate time of exposure. Then, fresh host egges
were offered to survived female wasps for parasitim for 24 h. The type of
functional response was determined using logistic regression and the
parameters including searching efficiency (a) and handling time (Th) were
estimated by non-linear regression. The results revealed a type II
functional response in the control and fipronil, and type III for diazinon. In
this study, application of insecticides caused a decrease in the attack rate
and an increase in the handling time of exposed wasps compared with the
control. The longest handling time (3.76 ± 0.4 h) and the lowest attack rate
(0.001 ± 0.0004) were observed in diazinon. The results suggested that the
adverse effect of this insecticide on searching ability of T. brassicae should
be considered in integrated pest management programs (IPM).
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