R. Ghorbani - Department of Plant Protection Research, Lorestan Agricultural and Natural Resources Research and Education Center, AREEO, Khorramabad, Islamic Republic of Iran.
A. A. Seraj - Department of Plant Protection, Faculty of Agriculture, Shahid Chamran University of Ahwaz, Ahvaz, Islamic Republic of IRAN.
H. Allahyari - Department of Plant Protection, College of Agriculture, University of Tehran, Karaj, Islamic Republic of Iran.
S. Farrokhi - Iranian Research Institute of Plant Protection, Agricultural Research Education and Extension Organization, AREEO, Tehran, Islamic Republic of Iran.

The egg parasitoid, Trichogramma evanescens Westwood, is used for inundative releases in biological control programs against the tomato leaf miner, Tuta absoluta Meyrick, in agro-ecosystems. One of the most important host-parasitoid interactions is functional response that its type and parameters are affected by different factors including host plant characteristics. In this research, functional response of T. evanescens to different egg densities (۲, ۴, ۸, ۱۶, ۳۲, and ۶۴) of T. absoluta was investigated in a growth chamber (۲۶±۲°C, ۵۰±۱۰% RH, and ۱۶:۸ hours L:D photoperiod), on three varieties of tomato (Mobil, Riogrande, and Early Urbana-۷۰۳). Type of functional response was determined by logistic regression and its parameters, i.e. searching efficiency and handling time, were calculated by nonlinear regression model using SAS software. Functional response of this parasitoid was type III on Mobil and Riogrande and type II on Early Urbana- ۷۰۳. Searching efficiency (a) for each host density was ۰.۰۳۶۸, ۰.۰۷۳۶, ۰.۱۴۷۲, ۰.۲۹۴۴, ۰.۵۸۸۸, and ۱.۱۷۷۶ on Mobil, and ۰.۰۳۷۴, ۰.۰۷۴۸, ۰.۱۴۶۹, ۰.۲۹۹۲, ۰.۵۹۸۴, and ۱.۱۹۶۸ h-۱ on Riogrande varieties, respectively. Also, on Early Urbana-۷۰۳, the attack rate was ۰.۱۰۴۵ h-۱. The handling time was ۱.۰۲۷۶, ۱.۱۰۱۷, and ۱.۳۲۸۹ hours with maximum parasitism of ۲۳.۳, ۲۱.۷, and ۱۸.۰۶ eggs on these varieties, respectively. It is suggested that physical structure of Early Urbana-۷۰۳ variety may interfere with the parasitoid’s performance, resulting in an impaired searching efficiency and parasitism ability. Some applied aspects of the findings are discussed.

Biological control, Host density, Search rate, Tomato moth, Trichogrammatids., واکنش تابعی, ارقام گوجه فرنگی