Apion rubens Walton, 1837
This widespread Western Palaearctic species is among the least common members of the genus and has a rather disjunct European distribution, it occurs more or less continuously from Spain to Italy and through the north to Denmark and Poland, it reaches into Southern Sweden and Norway but is absent from Finland and most of the Baltic countries, it also seems to be absent from much of Eastern Europe but is widespread in central and south-western Asia, Asia Minor and north-western Africa. In the UK it seems to be more frequent than in other North European countries; it is widespread and locally common across England and Wales north to the Humber though generally absent from the West Country, much more local and rare in North-East England and Southern Scotland and absent from Ireland. Adults are present year-round and may be very common where they occur, they overwinter in the soil or among litter etc. and appear on host plants from March or April, they peak in abundance from May until August and usually remain active into November. Typical habitats are grassland and scrub on light or sandy soils, often on coastal pastures and dunes but more generally on agricultural borders, moorland and road verges etc. where the host plants are abundant. The species is monophagous on Sheep’s Sorrell (Rumex acetosella L.), adults reproduce in the spring after a period of feeding upon tender foliage and females oviposit in stems and larger leaf veins from the end of May until the beginning of July. Larvae mine the stems and veins, producing long galls that turn yellow and then red as feeding continues, they are fully grown within a few weeks and pupation occurs within the galls. Heavily infested plants may display extensive galling and become stunted. New-generation adults appear from July until September; they rarely seem to move far from the host and at this time may suddenly appear in numbers. Sampling usually involves sweeping close to the ground among extensive patches of host plants, they are diurnal but secretive and we have had more success sweeping for these at night.
2.2-2.7 mm. An elongate and rather narrow species, body and appendages red and finely pubescent throughout, the pubescence is pale and more distinct than in our other members of the genus. Head slightly transverse, with large convex eyes and diverging temples, strongly and closely punctured except behind the eyes and ventrally where it is smooth and transversely strigose. Rostrum moderately strongly down-curved, in the male only a little longer than the head, in the female longer, as long as the pronotum, antennae in both sexes inserted near the middle and about as long as the head and pronotum combined. Pronotum slightly transverse, broadest about the middle and gently curved to obtuse posterior angles and a weak sub-apical constriction, surface moderately strongly and densely punctured, basal fovea short and often indistinct. Elytra slightly convex and only weakly dilated from rounded shoulders to a continuous apical margin, long (at least 3X the pronotal length) and often almost parallel-sided, striae strongly punctured to the apex, interstices weakly convex, transversely rugose and almost impunctate. Legs robust, femora simple, middle and hind tibia with a strong external spur, front tibiae simply rounded apically, claws free and toothed.