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Published online by Cambridge University Press: 27 March 2009
To determine economic thresholds of pest infestation caged plots of oil-seed rape (Brassica napus L.) were infested with different populations of the seed weevil (Ceutorhynchus assimilis Payk.). Less than one seed weevil per plant resulted in pod infestation levels of seed weevil larvae that by themselves were insufficient to warrant insecticide application, but owing to secondary infestation of pod midge (Dasyneura brassicae Winn.), substantial seed loss occurred. Greater populations of seed weevil adults gave correspondingly larger levels of pod midge and diminishing yields.
In commercial crops individual plants were able to compensate, and even to overcompensate for damage resulting from low levels of pest infestation, but increasing levels of infestation resulted in progressively fewer seeds per plant.
The implications of the results on pest control and further research are discussed.