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Title: Parasitism of aphids in canola fields in central Oklahoma

Author
item Elliott, Norman - Norm
item BACKOULOU, GEORGES - Oklahoma State University
item GILES, KRISTOPHER - Oklahoma State University
item ROYER, THOMAS - Oklahoma State University

Submitted to: Journal of Agricultural and Urban Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/22/2014
Publication Date: 10/1/2014
Citation: Elliott, N.C., Backoulou, G.F., Giles, K.L., Royer, T.A. 2014. Parasitism of aphids in canola fields in central Oklahoma. Journal of Agricultural and Urban Entomology. 30(1):59-64.

Interpretive Summary: Winter canola, Brassica napus L., production in Oklahoma has increased from essentially 0 ha in 2001 to 40,500 ha in 2011, and acreage is expected to continue to increase. Three aphid species typically infest canola fields in central Oklahoma, the turnip aphid Lypaphis erysimi (Kaltenbach), the cabbage aphid, Brevicoryne brassicae L., and the green peach aphid, Myzus persicae S. The expansion of canola acres in Oklahoma and the ubiquitous nature of aphid infestations in the crop indicate the need to understand the role of natural enemies in controlling aphid infestations. The purpose of this study was to determine the parasitoid species attacking aphids in the crop and the progression of parasitism during the flowering through pod development growth stages, when aphid populations often build to the point requiring insecticide treatment. Diaeretiella rapae (M'Intosh) was the dominant parasitoid of aphids in canola. Individuals of all three aphid species were parasitized by D. rapae. Parasitism of all three aphid species varied among fields, sample dates, and among aphid species. The observation that parasitism could not keep pace with the rate of population increase of green peach aphid and cabbage aphid suggests that biological control by D. rapae is currently insufficient to maintain aphid infestations below economically damaging levels. Future biological control research on canola should focus on devising ways to increase the effectiveness of D. rapae in controlling aphid infestations in the crop.

Technical Abstract: Winter canola, Brassica napus L., production in Oklahoma has increased from essentially 0 ha in 2001 to 40,500 ha in 2011, and acreage is expected to continue to increase. Three aphid species typically infest canola fields in central Oklahoma, the turnip aphid Lypaphis erysimi (Kaltenbach), the cabbage aphid, Brevicoryne brassicae L., and the green peach aphid, Myzus persicae S. The expansion of canola acres in Oklahoma and the ubiquitous nature of aphid infestations in the crop indicate the need to understand the role of natural enemies in controlling aphid infestations. The purpose of this study was to determine the parasitoid species attacking aphids in the crop and the progression of parasitism during the flowering through pod development growth stages, when aphid populations often build to the point requiring insecticide treatment. Diaeretiella rapae (M'Intosh) was the dominant parasitoid of aphids in canola. Individuals of all three aphid species were parasitized by D. rapae. Apparent parasitism rate ranged from 0 to 45% depending on aphid species, field, and sample date. Aphelinus spp. was recovered from cabbage aphid from field one on a single sample date, but was not recovered from aphids collected from other canola fields or on other sample dates. Apparent parasitism of turnip aphid was greater than apparent parasitism for cabbage aphid, ranging from 17 to 45% for turnip aphid compared to 2 to 12% for cabbage aphid. Apparent parasitism of green peach aphid was often slightly greater of cabbage aphid, but the difference in apparent parasitism rate of the two species was not significant. Apparent parasitism of turnip aphid increased from 15 to 28% during the study. Apparent parasitism of cabbage aphid and green peach aphid was usually lower than for turnip aphid, and initially increased but then decreased over the course of the study.