Lasiorhynchites cavifrons (Gyllenhal, 1833)
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POLYPHAGA Emery, 1886
CURCULIONOIDEA Latreille, 1802
RHYNCHITINI Gistel, 1848
LASIORHYNCHITES Jekel, 1860
This large and distinctive weevil is very local and generally rare throughout its range which extends from Spain across central Europe and Asia Minor to Azerbaijan and north to Denmark and the UK, in North Africa it is known only from Algeria; in the UK it is very local, although sometimes common, across Wales and Southern and Central England. Adults occur from April until July and are occasionally active in the autumn before they enter the ground to overwinter, the host is oak but they may occur adventitiously on other trees, typically in broad-leaved woodland but also wooded parkland or scrub where the host occurs, and they may be found on trees of any size, from seedlings to ancient specimens. They fly well and may occur away from the host; we once found a dead specimen on a bench remote from oak trees at Bricket Wood Common, Herts. Mating occurs in the spring and oviposition continues until the end of June; a single egg is inserted under the bark of a healthy twig just below a leaf axil, the female bores a hole about 1mm across and 1mm deep and peels back a strip of bark before depositing the egg, the hole is then filled with a secretion and the bark replaced, the whole process taking about an hour. The freshly emerged larva consumes part of the leaf bud and then bores into the twig to feed under the bark, eventually producing a mine some 2 or 3 cm long, it develops quickly and is fully grown by September or October when it will leave the mine, fall to the ground and burrow down to form a pupal cell. Late summer pupae produce adults which remain in situ until the spring but they may leave the ground and feed for a while before overwintering to emerge from April.
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With the exception of Lasiorhynchites olivacues Gyllenhal, 1833, the other UK species of the genus, L. cavifrons is distinct from other blue rhynchitids by its large size; from L. olivaceus it is distinguished by the ninth and tenth elytral striae remaining separate for their entire length; in cavifrons they merge near the middle of the elytra.
5.3-8.5mm, entire body metallic dark blue with rather long and erect dark pubescence, appendages darker though still metallic. Head transverse with weakly protruding convex eyes which are larger in the female, and relatively long, slightly curved temples, vertex convex and finely punctured, in the male strongly impressed between the eyes. Rostrum straight, expanded anterior to the antennal insertions and with a distinct median longitudinal keel. Pronotum quadrate, strongly rounded laterally and weakly constricted before the apical margin, surface convex and more strongly punctured than the head, often with a median longitudinal impression in the basal half. Elytra parallel-sided or nearly so, with broad and prominent shoulders and strongly punctured striae which tend to be confused, especially near the base, and evanescent beyond the middle, the ninth and tenth continue beyond the middle and remain distinct, interstices randomly and more finely punctured than the striae. Males are readily distinguished by the large depression below the vertex, also the rostrum is shorter and the pro-tibiae have 2 apical spurs, in the female only a single spur.