Study on the seasonal parasitism rate of the diamondback moth, Plutella xylostella (L.) (Lep.: Plutellidae) parasitoids in the cauliflower fields in south of Tehran

The diamondback moth, Plutella xylostella (Lep.: Plutellidae) is the most destructive insect pest of crucifer plants throughout the world. In order to identify its parasitoids and study on seasonal fluctuation of parasitism, sampling was conducted in the cauliflower fields of southern Tehran from June until October 2011. One hectare cauliflower field in the middle of a large field was randomly selected in Jahan-Abad, Kahrizak, Shokr-Abadand Palayin regions. A field with the area of 600 m2' in College of Agricultural Sciences, Shahed University, Tehran was selected as control with no insecticide treatment. Each plant was presumed as a sampling unit and sample size was determined as 20 host plants. Sampling was carried out every 14_day and all larvae and pupa on the host plant were collected and reared under laboratory conditions. Also parasitoids were collected with calling method. In the present study, three species of parasitoid wasps were determined. These parasitoids were Diadegma anurum (Thomson, 1877), Cotesia plutellae (Kurdjumov, 1912) and Oomyzus sokolowskii (Kurdjumov, 1912). The highest percentage of parasitism of larval and pupal stages were recorded 47.57 (July 14th) and the lowest were 22.33 (June 19th). The highest percentage of parasitism (12.14) in Shahed field was caused by D. anurum. The highest percentage of parasitism (57.49) was observed in Jahan-Abad region and the lowest (8.22) was in Palayin region. The results of this study showed that there is significant difference between percentage of parasitism in Shahed University field and other fields.