Anthonomus rubi (Herbst, 1795)
POLYPHAGA Emery, 1886
CURCULIONOIDEA Latreille, 1802
CURCULIONINAE Latreille, 1802
ANTHONOMINI Thomson, C.G., 1859
ANTHONOMUS Germar, 1817
ANTHONOMUS Germar, 1817
A locally common or abundant species throughout Europe from North Africa to the far north of Scandinavia and extending east through central Asia to China, in the UK it is generally common through south and central England and Wales although absent from most of the west country and local north of the Humber; in Scotland from the south west and sporadic in the northern Highlands. Adults occur year-round, they become active from March or April and are soon abundant, peaking in late May or early June, and persisting into August, typical habitats include unimproved grassland, wasteland, wooded borders and hedgerow margins etc., where they develop on a range of woody and herbaceous Rosaceae e.g. Geum, Potentilla, Fragaria, Rosa, Rubus and Cotoneaster. Throughout much of its range it is a sporadic and often serious pest of commercially grown strawberries, raspberries and blackberries and in some years huge populations may develop, being maintained by wild specimens breeding in wild situations. Freshly emerged adults feed for a few days on foliage before moving on to flowers, in both cases producing multiple small holes and in severe cases causing them to fall, but this damage tends to be insignificant as the females soon begin to oviposit. Eggs are laid from late April; the female chews a small hole into an unopened flower bud and inserts a single pale translucent egg, she then moves a short distance along the pedicel and bites several small holes around it margin, these damaged buds fail to open and either remain hanging on the plant or fall to the ground. Larvae emerge after 5 or 6 days and feed on the receptacle and other parts from within; they develop rapidly and are fully-grown, reaching about 2.5mm in length, within 2 weeks. Pupation occurs within the shrivelled bud and adults eclose after about 2 weeks, they emerge from the bud and feed for a week or two and then enter leaf-litter or tussocks where they will diapause through the summer and overwinter, emerging in the spring to continue feeding. Adults can be swept from vegetation generally, especially on wooded margins and along hedgerows, and are usually common on Crataegus blossom.
This is a small and rather non-descript species that nonetheless will soon become distinctive, in the sweep net they might casually be mistaken for an apionid but the antennal scape is distinct. 2.0-2.3mm entirely shiny black but for the variously pale antennal base, tibiae and tarsi, and immature specimens tend to be dark brown but the mature dark colour soon develops. Entire body and legs with sparse short pale pubescence which tends to form distinct lines on the elytra. Head transverse with prominent and weakly convex eyes and long parallel-sided rostrum. Antennal scape slender and weakly sinuate, gradually and only weakly expanded towards the apex and about as long as the head and pronotum combined, funiculus 7-segmented; pedicel elongate; at least 2X longer than wide, antennomeres 3-8 quadrate to transverse and the club elongate and pointed. Pronotum transverse and widest behind the middle, lateral margin without borders and gently constricted anteriorly, posterior margin gently sinuate, anterior margin smoothly curved and evenly convex; not raised. Pronotal surface quite densely and strongly punctured, otherwise without sculpture. Scutellum small but obvious, triangular and flat; without sculpture and often clothed with dense white scales, this is often useful for identification under a lens in the field. Elytra much broader across the base than the pronotum and rather distinctively broadened behind the middle, with well-impressed and strongly punctured striae which are complete from the base to the apex, and finely and sparsely punctured interstices. Legs long and robust, a feature that is well-demonstrated in flat carded specimens i.e. with the legs splayed rather than raised, femora distinctly though rather weakly thickened around the middle; pro-femora with a single sharp tooth below, tibiae slender and only weakly sinuate along the inner edges, outer margin smooth and only weakly curved to an apical angle or curve; not expanded externally, inner margin inwardly curved to a sharp apical tooth. Tarsomeres 1, 2 and 5 elongate, 3 widely bilobed and partially hiding the small fourth segment. Claws free, each with a large lobe at the base.