Apion frumentarium (Linnaeus, 1758)
This conspicuous and attractive species is generally common throughout Europe, except for the far north, southwest Asia and the Middle East; Turkey, Syria and Israel etc. Huge numbers, collected in Israel, have been released in Western Australia in the hope that they would become established as a biocontrol agent but this has so far been unsuccessful. In the U.K. it is common throughout England and Wales and very local in southern Scotland. Host plants include various Rumex species (docks) but especially R. hydrolapathum Huds., R. crispus L., R. obtusifolius L. and R. conglomeratus Murray, and the beetles may be found wherever they occur e.g. parks, gardens, waste ground and agricultural margins etc. Adults occur year round but are most obvious from April to July when they are active both on the hosts and also dispersing; at this time they may be seen on umbel flowers, and swept from long grass and nettles etc. Winter is passed low down in the stems or under debris and in tussocks and they may become active during warm spells when they may feed underneath Rumex leaves. They are active from early spring when they may be seen crawling on bare soil, especially on arable margins, and begin feeding on young host foliage producing small shot holes. Mating occurs from April and continues over a long period, at least into July. Females chew small holes into the stems and petioles in which they lay a single egg and seal the damage with a secretion, the larvae develop within the petioles, stems and roots, sometimes producing swellings or discoloured lines of dead epidermis as they go. They have a relatively long development period; about a month or so and pass through three instars before pupating, this stage lasts for five or six days and new generation adults appear from late May or June. They spend some time feeding before leaving the host to find summer aestivating sites, appearing again in late summer and autumn to continue feeding before heading for overwintering sites in October and November. In most years they will be seen through the winter on host foliage or on the ground near the host.
2.5-4.5mm. distinguished from our other species of Apion by the elongate head with temples at least one and a half times the length of the eyes; with the exception of a smooth and transversely wrinkled area on the underside in front of the anterior Prosternal margin the head is coarsely punctured throughout. The sexes differ in the form of the rostrum; in the male it is broader, less curved, and duller beyond the antennal insertions, in the female narrower, more curved and more evenly shiny throughout. The eyes and claws are black, otherwise the entire beetle is red and the dorsal surface is clothed with sparse creamy-white pubescence.
APION Herbst, 1797
This Palaearctic genus includes about 16 species, of which 9 occur in Europe and 5 extend north to the UK and Scandinavia. All members of the genus are quite distinctive, being entirely red but for the eyes and claws, and as such will not be confused with any other members of the family. They feed on various Polygonaceae; in Northern Europe on species of Rumex L. but elsewhere also on Polygonum L., Calligonum L. and Atraphaxis L. Larvae mine the stems, petioles and roots, causing galls, and more than one species may be present on a single plant. Adults occur year-round and during the summer may generate very large populations. With the exception of A. rubiginosum Grill, 1893, which is of local occurrence in southern and central England and Wales, our species are widespread and either generally or locally common.
Species vary from 2.2-4.5mm, A. frumentarium (Linnaeus, 1758) being our largest member of the family, and are elongate with weakly or strongly rounded elytra. Head quadrate to elongate, pronotum quadrate to transverse, both distinctly punctured, often strongly and densely so. The base of the head is often impunctate and transversely striate, eyes black and relatively large, varying from flat to very strongly convex and protruding, rostrum relatively short, cylindrical and thickened at the antennae insertions, and punctured, at least towards the base. Antennae long and slender, inserted behind the middle of the rostrum, with a distinct and fusiform 3-segmented club. Scutellum visible and usually elongate. Elytra with distinct and strongly punctured striae, interstices at least as wide as the striae, usually broader, finely punctured and pubescent, generally in 2-4 fairly distinct rows, and usually flat or only weakly convex on the disc.