Orchestes alni (Linnaeus, 1758)
Widespread and generally common across Southern and Central Europe including most of the Mediterranean islands but more sporadic and local further north to the UK, Denmark, Estonia and Latvia, this species extends into Eastern Asia but, contrary to some sources, does not occur in North America. In the UK it is locally common across Southern and Central England north to The Wash, local and mostly coastal in the south west and South Wales and sporadic and rare further north to South Yorkshire. Despite its specific name the species is associated with various elms (Ulmus L.), usually Field Elm (U. minor Mill. and its cultivars which include U. procera Salisb., commonly known as the English Elm), Wych Elm (U. glabra Huds.) and, further east, Siberian elm (U. pumila L.). Adults occur year-round and are active from April until July or August, peaking in abundance during June, they appear shortly before the host leaf buds burst and at this time may found on twigs and branches. Mating occurs in the spring after a period of feeding on host foliage and females chew small holes into the underside of main veins to insert eggs into unfolding leaves. The oviposition scar remains visible towards the leaf tip and from this the larva will mine towards the tip, creating an extensive blotch mine that is visible from above and below, and because females may extensively attack single plants the species is sometimes classed as a pest of ornamental stock. Larvae are fully-grown by June when they form spherical cells within the mine in which they will pupate. Adults emerge from pupal cells during June and July and feed on tender foliage, causing holes in leaves, but the main feeding phase will occur in the spring after they have overwintered under bark or among litter beneath host trees. Adult feeding is usually superficial but larval feeding can cause young leaves to turn brown and drop, and extensive infestations may weaken young trees. Adults usually occur in numbers and may be swept or beaten from elms in almost any situation, typically in open woodland or parkland but also from small trees in hedgerows or gardens, they also fly well and so are likely to occur suddenly in well-worked sites.
2.5-3.7 mm. Very distinctive and not likely to be confused with any other species, forebody small compared with the large oval elytra, characteristically coloured; head black, pronotum brown with the disc darker, elytra brown with darker markings, typically below the shoulders and transversely behind the middle which may extend along the suture in both directions, legs dark with pale tarsi and antennae substantially pale. Eyes large and occupying most of the head, the interocular distance narrower than the rostral width, antennae distinctly geniculate, the scape gradually broadened from the base, funiculus 6-segmented and the club elongate and pointed. Rostrum curved down and usually not visible, slightly longer in females but this is often not obvious. Pronotum transverse, widest about the middle and rounded laterally to obtuse posterior angles and a weak subapical constriction, surface roughly punctured and without a median longitudinal impression, pubescence consists of sparse long pale and erect setae. Elytra evenly curved from rounded shoulders to a continuous apical margin, striae impressed and strongly punctured to before the apex and interstices finely punctured throughout, pubescence mostly recumbent and directed towards the apex but also, especially in the basal half, with erect setae. Hind femora massively enlarged and with several small teeth along the ventral margin, middle and front femora normal, front and middle tibiae narrow, hind tibiae curved and expanded towards the apex. Tarsi pseudotetramerous with the third segment widely and deeply bilobed. Claws not united at the base, smooth internally and each with a large basal tooth or lobe.