Economic injury level and yield loss assessment caused by cabbage aphid (Brevicoryne brassicae) on rape (Brassica napus)

The rape crop was infested with 4 apterous- prelarviposition adult of Brevycoryne brassica L. and exposed to feeding for 0 (no exposure), 1, 2, 3, 4, 5, 6 weeks of exposure respectively and complete exposure (control). The results showed a significant reduction in the number of aphids per plant as the frequency of spraying increased. A significant inverse relationship between aphid exposure and yield was observed, being apparent after two weeks. Yield loss increased to more than 70% when the insecticide was not applied to control aphids.