Ceutorhynchus napi Gyllenhal Rape stem weevil

This weevil is a major pest of winter rape in France, Germany and Switzerland, and in other parts of continental Europe, but does not occur in the British Isles; infestations also occur on other crops, including cabbage and turnip. Most significant damage is caused by the process of egg laying within the elongating stems, rather than by larval feeding. Main stems typically twist and split open, especially following heavy rain or frosty conditions, and considerable distortion and disruption of growth results. Infested stems are often killed and plants then survive only by producing lateral shoots. Damaged plants are particularly liable to invasion by secondary organisms such as canker.

BIOLOGY

Adults appear in the early spring and then invade rape crops, eventually depositing eggs singly (cf. Ceutorhynchus pallidactylus, below) in the young, elongating stems, close to a terminal bud. The eggs hatch several weeks later and larvae feed within the pith of the stems for up to 6 weeks. They then vacate the host plant and enter the soil to pupate in an earthen cell. The adult stage is reached 3-4 weeks later but the weevils remain within their pupal cells throughout the winter (cf. C. pallidactylus, below).

DESCRIPTION

Adult 3.2-4.0 mm long, greyish, with distinct blackish longitudinal furrows on the elytra. Larva up to 7 mm long; body whitish at first but finally yellowish; head brownish-black in the first two instars, yellowish-brown in the third (Plate 5b).

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