Nastaran Rezaei - Department of Plant Protection, Faculty of Agriculture, Shahid Chamran University, Ahvaz, Iran.
Farhan Kocheyli - Department of Plant Protection, Faculty of Agriculture, Shahid Chamran University, Ahvaz, Iran.
Mohammad Saeed Mossadegh - Department of Plant Protection, Faculty of Agriculture, Shahid Chamran University, Ahvaz, Iran.
Khalil Talebi Jahromi - Department of Plant Protection, College of Agriculture and Natural Resources, University of Tehran, Karaj, Iran.
Aurang Kavousi - Department of Plant Protection, Faculty of Agriculture, University of Zanjan, Zanjan, Iran.

The toxicity of thiamethoxam and pirimicarb on Diaeretiella rapae (Mc'Intosh) as a parasitoid of Lipaphis erysimi (Kaltenbach), exposed to residues on glass vials, was investigated under laboratory conditions at ۲۳ ± ۲ °C, ۷۰ ± ۵% RH and ۱۶:۸ h (L: D). Moreover, in order to find the negative impacts of both insecticides on the efficiency of D. rapae, the functional response of the exposed parasitoids were assessed. The newly emerged parasitoids were exposed to LC۲۵ of the insecticides and distilled water as control. Host densities of ۲, ۴, ۶, ۸, ۱۶, ۳۲ and ۶۴ were placed on canola seedlings in a transparent cylindrical container and were offered to the treated parasitoids. Type of functional response was determined by means of logistic regression method and the parameters, attack rate (a) and handling time (Th) were calculated by nonlinear regression model using SAS software. The parasitoid exhibited type II functional response in all experiments. Attack rates in control, pirimicarb and thiamethoxam were ۰.۰۵۷ ± ۰.۰۱,۰.۰۵۹ ± ۰.۰۱۳ and ۰.۰۴۰ ± ۰.۰۱ h-۱, and handling times were ۱.۰۹۷ ± ۰.۱, ۱.۸۶ ± ۰.۰۲, ۲.۸۱ ± ۰.۲۹۶ h, respectively. Maximum rates of parasitism (T/Th) were estimated ۲۱.۸۷, ۱۲.۹, ۸.۵۳ aphids, respectively. These observations suggest that pirimicarb with less harmful effects is the preferred candidate for controlling the mustard aphid.

Diaeretilla rapae, Lipaphis erysimi, functional response, thiamethoxam, pirimicarb