population dynamics of canola aphids and their dominant natural enemies in ahvaz

in this research, population fluctuation of canola aphids and their natural enemies were investigated during 2007-2008. random samples of 50 plants were taken twice a week. mustard aphid (lipaphis erysimi kalt.), green peach aphid(myzus persicae sulzer)and cabbage aphid (brevicoryne brassicae l.) were recorded on canola. however,the mustard aphid with relative frequency of 79% was dominant. the cabbage aphid and green peach aphid ranked second and third with relative frequencies of 12% and 9% respectively. the mustard aphid appeared in mid december, the green peach aphid in late december-early january and the cabbage aphid in mid february. the mustard aphid and green peach aphid peaked in middle of march and cabbage aphid peaked in late of march, then after their number decreased in late april. predatory species coccinella septempunctata l., episyrphus balteatus de geer and chrysoperla carneastephens with the relative frequencies of 69%, 24% and 7% were collected on canola respectively. coccinellids, syrphids and chrysopids peaked in middle of march, late of march and in middle of april, respectively. prasitoiddiaeretiella rapae mclntosh and two hyperparasitoids pachyneuron aphidis bouche and aphidencyrtus aphidovorus mayr were obtained from mummies. the highest percent of the parasitism was 32% in late march, early april and the average precent of parasitism was 13%.