Ceutorhynchus picitarsis Gyllenhal, 1837
This generally common and often abundant weevil occurs throughout western and central Europe north to the Baltic coast and the UK and east to Asia Minor, it is also present on various Mediterranean islands and widespread in northwest Africa but absent from the Atlantic islands. In the UK it was formerly very local and scarce in the south of England but in recent decades has become much more common and widespread; the distribution is mostly eastern with many records from the southeast, East Anglia and south Yorkshire, it is absent from many western areas but there are sporadic records from the midlands to north-eastern Wales. Adults occur year-round; typical habitats are verges, field margins and disturbed ground generally, they are associated with various wild and cultivated Brassicaceae but may become abundant among agricultural crops. Host plants include tall hedge mustard, Sisymbrium loeselii L., cabbage (etc.), Brassica oleracea L. (and cultivars), turnipweed, Rapistrum rugosum (L.), perennial wall-rocket, Diplotaxis tenuifolia (L.), bittercress, Barbarea vulgaris Aiton, and dyer’s wood, Isatis tinctoria L. but the host of interest is oilseed rape, Brassica napus L. as the weevil is an occasional serious pest throughout its range. Adults spend the summer on wild plants and move onto young crops during September and October, mating occurs from late summer and oviposition begins in September, adults overwinter and may continue ovipositing during mild spells into February or March. Eggs are laid singly or in small groups on the underside of leaves at the bases of host petioles or on the stems, the freshly-emerged larvae feed on leaves for a while before they bore into soft stem tissue, here they feed throughout the winter, working their way down the stems as they do so, and end up in the root-collar when fully grown. During March and April they bore out of the stem and enter the soil to pupate in a subterranean cell. Adults emerge during late spring and summer and enter a resting phase before feeding and mating begins in late summer. During the spring when the young plants begin to grow those affected can be recognized by their stunted growth or profusion of lateral stems following the destruction of the growing tip, in extreme cases where infestations have been severe whole plants or groups of plants may die off before the larvae bore out of the stems. The legless larvae are small, 4.5mm long when fully grown, C-shaped and white with a brown head, they may be found by opening stems of stunted plants in early spring. Adults may be found by sweeping mixed herbage, especially in disturbed habitats, but sweeping among oilseed rape in the spring and autumn may produce them in abundance.
Adults may be recognized by the relatively large size, 2.6-3.6mm, and general colouration; entirely black with red tarsi and a patch of yellow scales on the mesepimera which are visible from above and contrast against the pale ventral scaling, in some specimens there is a patch of pale scales behind the scutellum and/or pale scales along the centre of the pronotum. Head densely punctured between large and convex eyes, rostrum long, thin and curved, antennae long and slender, the scape gradually and only weakly thickened in the apical third, funiculus 7-segmented. Pronotum broadest across the base, weakly-curved and narrowed laterally to a raised apical margin, surface with a small, blunt tooth either side of the disc. Elytra elongate, about 1.25X longer than wide, with sloping shoulders and lateral margins contracted to an obliquely truncate apical margin, striae deeply impressed and punctured, interstices flat and lacking scales, finely punctured and with recumbent pale setae which are clearly visible along the margins, each with several small tubercles before the apical margin. Legs long and robust; femora not toothed internally, middle and hind tibiae with long apical spurs in the male, unarmed in the female, tarsi pseudotetramerous with the third segment strongly bilobed. Tarsal claws appendiculate.