Ceutorhynchus pallidactylus (Marsham, 1802)
Cabbage Stem Weevil

This native and widespread Palaearctic species of weevil, notorious for the damage it causes to cultivated Brassica crops, is now virtually cosmopolitan and established as a pest wherever suitable crops are grown; it is a serious pest of spring-sown oilseed rape in many European countries, North Africa, Asia, Canada and America. In the UK it occurs commonly throughout England and Wales on both cultivated and wild Brassicas and has also been recorded on various Resedacaea and occasionally Hemp, Cannabis sativa. In the spring and early summer sweeping field margins where suitable crops are grown will produce the adults in abundance but beyond this they occur in a wide range of habitats; parkland, gardens and waste ground etc. although usually in small numbers. The adults overwinter among litter etc. near the host plants and become active in the spring when the soil temperature reaches 8 or 90C, at this time they may fly if necessary to find host plants but most of their time is spent on the ground or on host stems. They feed on tender stems and leaves but the damage they cause is insignificant, oviposition occurs during April and May when females bore small holes into the stems at the bases of petioles and insert small batches of 3 or 4 eggs; each beetle will produce about 40 eggs and the stems will discolour and enlarge around the oviposition sites. Larvae hatch after a week or so and bore down the stems, sometimes reaching the roots, and damaging the plants as they go; in severe infestations each stem will host a number of larvae and many will wilt and die off. Larval development is rapid and they are fully grown in about 3 weeks, during June and July they bore their way out of the stems, or sometimes enlarge the oviposition holes for the purpose, and make their way into the soil where they will pupate in a cell 4 or 5 cm below the surface. The pupal stage lasts about 2 weeks and new generation adults appear from late June to August, these will feed until the autumn when they will enter the leaf litter to overwinter. The economic significance of this species can be drastic; larvae may destroy seedlings and severely reduce the growth of young plants, and it has been shown that seed yield and seed growing capacity decreases from infected plants. Deep autumn ploughing is used to reduce their numbers but pesticides are still commonly used to control infestations.