Rhinocyllus conicus (Frölich, 1792)

This native species of southern and central Europe, western Asia and North Africa has spread in recent years to many northern areas including the U.K. During the 1930’s populations from France were released in several locations in Canada and the United States to help control the noxious invasive milk and plumeless thistles, also introduced from Europe, albeit accidentally, but this was too successful and the weevil began destroying native species and so its use is no longer recommended and in many areas its release is prohibited. In the U.K. formerly restricted to southern coastal areas from Cornwall to Kent but following a recent and continuing expansion it is now locally common across England and Wales, and it seems to be increasing in abundance. The species occurs on a range of thistles, Asteraceae, including members of Carduus, Cirsium, Onopordum and Silybum; during the summer the adults are readily observed on stems just below the flowers, often several to a stem. Locally we tend to find them mostly on spear thistle, Cirsium vulgare. They become established in open sites wherever the host thrives; waste ground, wood and arable borders and unmanaged grassland etc. Adults overwinter among plant debris near the host and become active in late spring when they feed on host foliage for a short while before dispersing by flight. Mating and oviposition begins in early summer; eggs are laid individually onto flower bud bracts and protected with a covering of chewed leaf material, these ‘caps’ turn pale brown after a few days and become easily visible around the flower. Each female will lay up to 200 eggs and a number may be deposited around a single flower. Larvae emerge after about ten days and feed below the developing seeds, development takes about six weeks and fourth (final) instar larvae construct a tough pupal cell from chewed plant material and frass; many cells may be present on a single flower and may fuse to form a large dark mass. New generation adults eclose after a week or two but remain in the cell for several weeks before chewing an exit hole to emerge, they will feed on leaves near the tops of stems producing characteristic round holes over the entire leaf surface. These adults will go on to overwinter but in some areas those emerging in midsummer with a day length >16 hours will produce a second generation.