Amalus scortillum (Herbst, 1795)
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POLYPHAGA Emery, 1886
CURCULIONOIDEA Latreille, 1802
AMALINI Wagner, 1936
Amalus Schönherr, 1825
This species occurs locally in throughout Europe from the Pyrenees to Italy and the Balkan peninsula in the south and reaching into UK and the Arctic Circle in Sweden although it is absent from some of the northern Baltic countries, it seems to be absent from most of the Mediterranean islands and does not occur in North Africa. To the east it extends through Ukraine and Russia into Siberia and Mongolia and has recently (2019) been recorded from China. Following introductions the species is now established in North America and is widespread across Canada and northern parts of the United States. In the UK it is locally common across southern and central England but generally scarce further north to southern Scotland and generally coastal in Wales. Adults are present year-round; they overwinter litter or in tussocks near the host plants and are active from May until September, peaking in abundance during May and June. Typical habitats open grassland, heathland and scrub, often on light sandy soils, but they often occur in ruderal places such as roadsides, waste ground, agricultural borders and even domestic gardens. In the UK the usual host is Common knotgrass, Polygonum aviculare L. but on the continent they also use various docks, notably Broad-leaved dock, Rumex obtusifolius L. and Sheep’s-sorrel, R. acetosella L. Mating occurs following a period of feeding in the spring and females lay small batches of eggs at the base of host stems during April and May. Larvae mine the root collar and work their way down into the roots, they develop quickly and when fully grown leave the roots to pupate in a cell nearby and new generation adults appear from June. Adults spend much of their time under host foliage and so the best way to sample them is to carefully lift groups of spreading stems and shake them over a net, this concealed way of life probably means the species is under-recorded but they sometimes appear when sweeping vegetation generally and they have often been recorded at light traps. Adults rarely occur in numbers although where the host is common they tend to infest several adjacent plants.
1.7-2.2 mm. Body dark grey to dark reddish-grey, sometimes with the elytra becoming reddish apically, with very fine pale pubescence, antennae pale but usually extensively darkened towards the apices, legs orange with the tibial apices and tarsi variously darkened. Head weakly depressed between large convex eyes, entire surface densely and moderately-strongly punctured, rostrum long, parallel-sided and evenly curved downwards. Antennal scape rather abruptly thickened in the apical third, funiculus 6-segmented and the club broad and pointed. Pronotum transverse, broadest about the middle and rounded laterally to a straight apical margin which is much narrower then the medially-produced basal margin, surface evenly convex and strongly though discretely punctured throughout, laterally with dense rounded pale creamy scales which cover the prosternum and are usually present along the posterior margin of the eyes. Anterior prosternal margin smoothly curved, not excised, front coxae very narrowly separated. Meso- and metasternum also with pale creamy scales which are visible from above on the ascending mesepimera and are often present along the basal pronotal margin. Elytra broadly-oval, slightly elongate and smoothly curved from obtusely-angles shoulders to a continuous apical margin, striae punctured and deeply-impressed, interstices only a little broader than the striae, strongly cross-rugose and rather flat, the sutural interstice with a characteristic elongate patch of broad pale scales behind the scutellum and usually more towards the apex. Femora unarmed. Middle and hind tibia with a small apical spur in males, unarmed in females. Claws free and with a small but sharp internal tooth. The species is usually obvious in the field; the patches of pale pubescence against the dark body, and the pale legs are distinctive.