Impact of Irrigation Systems on Seasonal Occurrence of Brevicoryne brassicae and Its Parasitism by Diaeretiella rapae on Canola
Seasonal population dynamics of Brevicoryne brassicae (L.) and Diaeretiella rapae (McIntosh) were studied in two canola (Brassica napus) fields with two different irrigation methods (flooding and sprinkler irrigations) from April to June 2010. Aphid and parasitoid (mummies) populations were sampled once a week. The highest aphid density was recorded on May 12th (792.5 ± 55.5) and on May 18th (1701.1 ± 195) in the sprinkler and flood irrigated fields, respectively. Parasitism rate recorded ranged from 0.4 to 19.5% and from 1.0 to 11.9% in sprinkler and flood irrigated fields, respectively. During the course of the study, there was no significant relationship between the weather values recorded and aphid populations observed in the field. However relationship with weather values was found in the case of D. rapae populations. Secondary parasitism was higher at the end of growing season and two hyperparasitoid species were dominant: Pachyneuron aphidis (Bouche) and Alloxysta fuscicornis (Ashmead). We discuss role of seasonal parasitism and irrigation systems for management of B. brassicae.
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