Effects of biorational insecticides on some biological features and functional response of the egg parasitoid trichogramma evanescens westwood (Hymenoptera: trichogrammatidae) exposed at differen pre-imaginal stages

In this study, the effects of different doses of biorational insecticides, namely Spinosad, Emamectin benzoate and Lambda cyhalothrin (positive control) on the emergence percentage (%) of Trichogramma evanescens Westwood (Hymenoptera: Trichogrammatidae) at different biological stages were investigated. The stages included larvae (2 days old), prepupae (4 days old) and pupae (6 days old) at 26±1 ̊C temperature, 65±5% relative humidity and 16:8 L:D photoperiod conditions. Anagasta kuehniella Zeller (Lepidoptera: Pyralidae) egg cards consisting of 100 parasitised eggs by T. evanescens at different biological stages to five doses of the insecticides (FR (Field rate), FR/2, FR/4, FR/8 and FR/16) and negative control (distilled water) for five seconds. T. evanescens % adult emergence was significantly reduced depending on the Spinosad doses when compared to control treatments. The highest % parasitoid emergence was recorded at 10.76 % at the FR/16 dose of Spinosad when exposed to the prepupal period (4 days). Additionaly, no emergence occurred when T. evanescens was exposed at larval stages (2 days old) to FR, FR /2 and FR /4 doses of Spinosad. Treatment of T. evanescens larval stage (2 days) with the FR dose of Emamectin benzoate yielded the lowest % adult emergence at 3.19 %. However, the highest % emergence (64.26 %) was obtained when parasitoids at the pupal stage (6 days old) were exposed to the FR/16 dose of Emamectin benzoate. Lambda cyhalothrin had the least sublethal effects on % emergence of T. evanescens at all doses and preimaginal stages. In conclusion T. evanescens treatment with different doses of biorational insecticides adversely affected the emergence percentage of the parasitoid. Spinosad and Emamectin benzoate were highly toxic for the preimaginal stages of T. evanescens while Lambda cyhalothrin was safer in comparison to the biorational insecticides. Therefore, it can be used safely in Integrated Pest Management (IPM) control programs of lepidopteran pests. The functional response of Trichogramma evanescens was studied with females that emerged from host eggs treated at the prepupal period (4 days old) with FR/16 doses of Lambda cyhalothrin and Emamectin benzoate under laboratory conditions (temperature of 26±1 ̊C, relative humidity of 65±5% and 16: 8 L:D photoperiod). The experiments were conducted with five different densities of Anagasta kuehniella (N0=5, 10, 20, 40, 80) for 24 hours. The response of females treated with Emamectin benzoate to different host densities was neutral and was similar at all exposed egg densities. However, T. evanescens females treated with Lambda cyhalothrin and control treatments showed significant differences in host exploitation which increased with increasing host egg density. T. evanescens showed Type II linear functional response in both insecticides and control treatments. T. evanescens attack rate (a) was higher in the control treatment than in Emamectin benzoate and Lambda cyhalothrin. The handling time (Th) of T. evanescens did not differ in all treatments. The simulated attack rate (T/Th) of T. evanescens was the lowest in the Emamectin benzoate treatment.