This generally abundant beetle is associated mainly with members of the Brassicaceae. The
adults and larvae often cause damage to oilseed rape, white mustard and other brassica seed crops, including cabbage and swede. Adults bite into the buds and this leads to abortion and, potentially, loss of yield. On winter rape, which has considerable powers of compensation and is usually past the vulnerable bud stage before the majority of adults emerge from hibernation, economic damage is rare; spring rape is more vulnerable and also more susceptible, as it flowers later in the season and is less robust. Larvae, which feed in the open blossoms, may also cause abortion of young pods but such damage is of little or no significance. In recent years, large numbers of young adults reared on oilseed rape crops have migrated to, and caused damage to, autumn-grown vegetable crops, especially the developing heads of calabrese and cauliflower; the beetles also invade various ornamental flowering crops in search of pollen, and have often then become a local nuisance.
Adults appear in the spring, from late April or early May onwards, and are usually active until June. They often congregate in large numbers on brassicaceous plants, including oilseed rape and weeds such as Sinapis arvensis, where they bite into the buds and opening flowers and feed on the anthers and exposed pollen. Eggs are laid in the flower buds and hatch about 7-10 days later.
The larvae develop within the opening buds and flowers for 3-4 weeks, passing through just two instars. Fully grown individuals then drop to the ground where they eventually pupate, each in a small earthen cell. New adults emerge in July. They then migrate to open flowers of various kinds of plant, where they feed on pollen. They then seek suitable overwintering quarters in the soil. There is only one generation a year.
Adult 1.5-2.7 mm long, mainly black, with a metallic bronzy-green tinge; elytra finely punctured (Fig. 208). Egg 0.8 x 6.3 mm, elongate with rounded ends, translucent-whitish. Larva up to 4 mm long; body creamish-white, with dark brown to black thoracic and abdominal plates; head black; legs blackish (Fig. 209); anal plate slightly indented posteriorly (cf. Meligethes viridescens, below).
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