Cabbage Seed Weevil (Ceutorhynchus assimilis)

Cabbage seed weevil adults are a dull, ash-grey colour and around 2-3 mm in length with a long narrow snout. They emerge from hibernation from late April and fly into the crop. Although the adults feed on the buds and pods they cause little damage, the main damage is caused by their larvae and the larvae of the brassica pod midge Dasineura brassicae, which lays its eggs inside the pod via the holes created by the cabbage seed weevil.

An adult cabbage seed weevil can lay up to 50 eggs, generally one per pod, and the larva can destroy up to a quarter of the seeds present in a pod. The mature larva will, after 4-5 weeks, bore a pin-head sized hole in the pod wall, drop to the ground and pupate in the soil.

There is generally a good relationship between the number of adult weevils found in the crop and subsequent damage to the seeds. It is recommended that the control of this pest be directed at the adults prior to egg laying, so therefore sampling must take place during the flowering period.

Control is aimed at the adults to minimise the harm done by the control method to the parasitoid Trichomalis perfectus, which parasitises the larvae of the cabbage seed weevil. Larval mortality rates of over 70% have been reported in crops not treated with insecticide.

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