Parasitism on cabbage aphid, brevicotyne brassicae [linnaeus] [homoptera: aphididae] associated with canola plants in Assiut

ABSTRACT

Thirteen cultivars of canola were subjected to evaluate the percentage of parasitism on cabbage aphid, Brevicoryne brassicae L. infesting canola plants in the field and laboratory during 2011 season in Assiut Governorate. The rate of parasitism in the field was [7.13%] for all cultivars. The rate of parasitism of the aphid collected from the field and reared in the laboratory was 2.67% times higher than the rate of parasitism in the filed at the end of season regardless the canola cultivars. The highest rates of parasitism were recorded with the early ripening cultivars, while the lowest ones were realized with the late ripening cultivars. In the field, the rate of parasitism increased progressively during the third week of February to a peak level [parasitism 43.15%] in the second week of March. Whereas in the laboratory, the highest rate of parasitism [53.06%] was achieved during the last week of February and then the parasitism started to decrease gradually during March. Two primary parasitoids species [Diaeretiella rapae McIntosh and Praon necans Mackauer, Aphidiidae] and two hyperparasotoids species [Alloxysta sp., Cynipidae and Chalcids sp., Chalcididae] were associated with cabbage aphids in canola fields. D. rapae consider the most important primary parasitoids on B. brassicae which represented about 93.93% of the total primary parasitoids in canola field. While, Alloxysta sp. was the most hyperparasioid represent 81.67% of the total of the secondary parasitoid. However, the primary parasitoids recorded the most percentage [71.94%] comparison with the percentage of secondary parasitoids [28.06%] from the total parasitoids for primary and secondary parasitoids