Archive of SID nd Proceedings of 22 Iranian Plant Protection Congress, 27-30 August 2016 588 College of Agriculture and Natural Resources, University of Tehran, Karaj, IRAN Difference between two populations of Trissolcus vassilievi in terms of functional response to sun pest eggs Bena Molaei, Parisa1, Iranipour, Shahzad2 and Asgari, Shahryar3 1.Assistant Professor, Department of Animal Biology, Faculty of Natural Science, University of Tabriz, Tabriz, Iran 2.Professor, Department of Plant Protection, Faculty of Agriculture, University of Tabriz, Tabriz, Iran 3.Research Assistant Professor, Agriculture and Natural Resource Research Center of Tehran Province, Varamin, Iran. P.benamolaei@ tabrizu.ac.ir Egg parasitoids have an important role in reducing sunn pest, Eurygaster integriseps Puton populations. Trissolcus vassilievi (Mayr) is one of the most important biological control agents of the sunn pest. Parasitism rate of host population depends on number of foraging parasitoids and per capita attack rate. The best way to understand parasitism components is distinguishing two kinds of parasitoid reactions i. e. functional and numerical responses that are important criteria in preliminary screening of parasitoids in biological control programs. In this study, two populations of both the parasitoid and the host, one from a colder region (Tabriz) and the other from a warmer region (Varamin) were used. The functional response experiments were carried out by offering 1, 4, 7, 14, 28, 56 and 84 host eggs of each population in respectively 50, 20, 10, 10, 5, 5 and 5 repetitions to 24 h-old fertile females of T. vassilievi (3rd generation of each population as well as females obtained from reciprocal crosses of them) for either 6 or 24 h. The experiments were conducted inside a growth chamber (26±1°C, 50±5% RH and 16L: 8D h photoperiod). Logistic regression analysis revealed that the functional response of T. vassilievi was from type III in all treatments. Parameter estimation also revealed that searching rate (b) and handling time (Th) was close to each other in all treatments. Rarely more than 10% difference was observed among treatments in terms of parasitism rate at different host densities. Maximum 13.5% difference was recorded in handling time and maximum attack rate in crossed populations proportional to the original populations. Experiment time had no considerable effect on parasitism rate and only unrealistically increased the handling time and decreased the line slope of the attack rate. Maximum attack rate varied between 42 and45 in original populations vs. maximum 47.5 in crossed populations. Handling time was longer and, parameter b smaller in Tabriz wasps. This may suggest that attack rate increases more rapidly in Varamin wasps. In other words, they have stronger density depended reaction. Host effect was not significant among treatments. This study showed that Varamin wasps have a minor superiority in terms of attack rate and searching ability. Keywords: parasitoid wasp, biological control, searching rate, handling time, host population. www.SID.ir .