Ceutorhynchus pallidactylus Marsham Cabbage stem weevil

This widely distributed pest is common on Brassicaceae, and often a problem on spring-sown brassica crops. Larvae feed within the stems and petioles, reducing plant vigour; heavy infestations on spring-sown brassica seed crops may significantly reduce yields. Larvae that attack spring-sown Brussels sprout, cabbage and cauliflower seedlings can also cause serious damage, infested plants becoming stunted and deformed and the inner tissue spongy and brittle; also, the stems of infested seedlings often break when the seedlings are transplanted. Larval infestations on winter rape often occur in the lateral shoots but are of little or no significance. When numerous, young adults emerging in summer can cause considerable damage to vegetable brassicas, as they browse on the leaves and bite into the underside of the petioles, mid-ribs and other major veins, which then become scarred and, sometimes, distorted.

BIOLOGY

Adults emerge from hibernation from mid-April onwards and then feed on various brassicaceous hosts, including brassica seed crops and vegetable brassicas. Eggs are laid from mid-May onwards. They are placed in groups of five or six

Ceutorhynchus Napi
Fig. 230 Cabbage stem weevil, Ceutorhynchus pallidactylulus (X20).

within the stems and petioles (cf. Ceutorhynchus napi, above), and this causes slight blistering. The eggs hatch 1-4 weeks later. Larvae feed during late May and June, tunnelling within the pith and often forming extensive galleries. When fully grown, 3-6 weeks later, they vacate the plants to pupate in the soil close to the surface. New adults appear in July or early August, and feed briefly on brassica plants before overwintering in the shelter of field margins and so on (cf. C. napi, above).

DESCRIPTION

Adult 2.5-3.5 mm long, greyish-brown and with a whitish patch of scales on the back, just behind the thorax (Fig. 230) (Plate 5c); body noticeably larger and more quadrate than that of Ceutorhynchus assimilis (p. 154); legs reddish. Egg 0.7 x 0.6 mm, oval, translucent, smooth, shiny. Larva up to 6 mm long; body creamish-white and elongate (Fig. 231); head pale yellowish-brown.

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