Bayer CropScience - Pestspotter - Rape winter stem weevil

Pest: Rape winter stem weevil

Identification
The adults are 2.5 - 4mm long , metallic black with reddish-brown tips to the legs. The white larvae have brown heads, are legless, are 4-5 mm long and `C` shaped.

Symptoms
The main shoots or whole plants can be killed by the larvae tunnelling and feeding in the stems. In the spring, at the beginning of stem extension, plants remain stunted and produce lateral shoots and the larvae can be found feeding in the stems when cut open.

Life cycle
The adults move into rape crops in late September and October and lay eggs on the upperside of the leaf petioles. Egg laying can continue throughout the winter as long as weather conditions remain mild. The larvae tunnel into the stems and feed throughout the winter until exiting in March / April to pupate in the soil. The adults emerge in the summer and after a resting phase move into rape crops to feed and lay eggs in the autumn.

Importance
Up until 1982 this pest was relatively uncommon in the UK, but has increased locally in parts of Lincolnshire, as far north as Scotland and may be becoming more common in East Anglia.

Threshold
Not established.