Ceutorhynchus picitarsis Gyllenhal Rape winter stem weevil

This weevil is a local and usually uncommon pest of winter brassica crops, including oilseed rape,

Fig. 231 Larva of cabbage stem weevil, Ceutorhynchuspallidactylus (x12).

swede and turnip. The larvae feed gregariously within the petioles, stems and crowns, and heavy infestations result in extensive hollowing and rotting of the tissue (Plate 5d), stunting, malformation and, sometimes, death of plants. Surviving plants often develop without terminal shoots, these being replaced by numerous weak lateral shoots that flower later than normal and yield poorly.

BIOLOGY

Adults occur in the autumn, eggs being laid mainly from mid-October to mid-November. The larvae feed inside host plants from October onwards. They pass through three instars and become fully grown in the following spring. Pupation takes place in the soil a few centimetres below the surface. New adults appear from mid-May to early June. They aestivate during the summer, in litter at the edges of woodlands and in hedgerows, and reappear in September or October.

DESCRIPTION

Adult 2.2-3.5 mm long, mainly shiny black, with a distinctive, pale yellowish mark on the 'shoulder' of each elytron; legs partly reddish. Larva up to 6mm long; body white; head brown.

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