Effects of diazinon and fipronil on functional response of Trichogramma brassicae Bezdenko (Hym.; Trichogrammatidae) in the laboratory conditions

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).