Rhynchites bacchus (Linnaeus, 1758)
This very widespread Palaearctic species occurs continuously from Spain through central Asia to China; it is most prevalent in warmer southern regions and occurs throughout North Africa, northern parts of the Middle East and Asia Minor, its European range is mostly southern and central but extends rather patchily north to the Baltic coast although it does not occur in Fennoscandia or the UK. There are a few 19th century records from southeast England but it was last recorded in 1843 and so its origins are unclear but if it was native it is now presumed to be long extinct. On the continent adults appear during March or April after overwintering in the soil, and both sexes feed on developing buds, flowers and fruits, mating occur soon afterwards and oviposition begins as soon as the fruits begin to swell, usually from late May. Females chew small cavities into developing fruits and lay a single egg, sometimes several females may lay into a single fruit but here the resulting larvae become cannibalistic and only one will survive, afterwards she severs the stem so that the fruit falls to the ground. Each female may lay up to 250 eggs and oviposition continues into July or August when the adults die off. Larvae emerge after a week or so and feed mostly on the fruit but may also consume the seeds, the fallen fruit is immediately colonized by the fungus Monilinia fructigena Honey, (1945), a type of brown rot which softens the fruit and makes it easier for the larva to feed, and this is introduced by the female at oviposition, larvae pass through three instars and are fully developed within three to eight weeks depending on temperature etc. The mature larva leaves the fruit and burrows into the ground and at this stage most will enter into a diapause which lasts until early the following year when they pupate in situ, but some will pupate during the first summer and produce overwintering adults. The pupal stage lasts about two weeks, late summer/autumn adults remain in the ground for a week or two and then emerge to feed on buds and developing leaves for a while before entering the ground to overwinter, freshly eclosed spring adults remain in the ground for a while to develop fully before emerging to begin feeding.
Rhynchites bacchus 1
Rhynchites bacchus 2
Adults are large, 4.0-6.0mm, brilliant golden green in colour, sometimes with blue or purple reflections, and superficially resemble R. auratus (Scopoli, 1763) but in that species the rostrum is entirely brilliant coppery or purple while in the present species it is black from the antennae insertions to the apex. Entire body with long semi-erect pubescence which is dark brown above and paler below. Head transverse, with small convex eyes and long diverging temples, surface moderately strongly punctured throughout, including the rostrum; male rostrum shorter, about as long as the head and pronotum combined, female rostrum longer. Pronotum rounded laterally, widest behind the middle and weakly constricted about the apical third, surface punctation about the same or a little stronger than that on the head. Males are easily distinguished by the presence of a sharp lateral tooth towards the pronotal apex. Elytra much wider than the pronotum, with broadly rounded shoulders and weakly dilated in the apical half, apical margin almost straight medially, leaving at most the pygidium exposed. Elytral with strongly punctured striae but lacking a scutellary striole, interstices more finely punctured throughout and distinctly rugose in places; the interstitial punctures and wrinkles often make the basal sculpture confused and it may be difficult to appreciate the lack of a scutellary stria but looking down the surface at a very shallow angle will usually reveal the striae. Legs black with a dark blue or violet metallic reflection, antennae black.