Anisandrus dispar (Fabricius, 1792)
Widespread and locally common throughout Europe from Spain to Greece and north to the UK, Denmark and into some southern provinces of Fennoscandia, also recorded from North Africa but apparently absent from most of the Mediterranean islands, this species occurs mostly in wooded lowlands, foothills and valleys and is rarely recorded from higher altitudes. The species is also recorded sporadically through Asia Minor and Russia to eastern Siberia and northern China and is widespread across the northern United States and Canada; it was unintentionally introduced in the early 19th Century and was the first invasive scolytid to be recognized in the region. In the UK it is widespread though local and generally scarce across central and southeast England and Wales, there are a few records further north and from the West Country but it is not recorded from Scotland or Ireland. Adults occur year-round; they overwinter in bark or wood and are active from April until September or October, peaking in abundance during May and June. Hosts include deciduous trees from a range of families as well as, much less frequently, various conifers, Frequently recorded hosts include Birch (Betula pendula Roth.), oaks (Quercus L.), poplars (Populus L.) and elms (Ulmus L.) but the species is sometimes a pest of various fruit trees e.g. it is an important pest of commercially grown Hazel ( Corylus avellana L.) in Mediterranean areas, and outbreaks are occasionally very damaging to orchards and vineyards throughout the range, including North America. The common name of Pear Blight Beetle is sometimes used as the species is known to spread its symbiotic fungus, Ambrosiella hartigii Batra (Ascomycota, Ceratocystidaceae), and females can only become sexually mature after overwintering and feeding on the ambrosial from of the fungus. Under laboratory conditions ovary development has been linked to seasonal variations of the fungus in mesonotal mycangium, and the fungus has been shown to be essential for larval development and pupation. Adults swarm in the evening during April and May and swarms often consist mostly of females, they generally infect dead or dying areas of wood but stressed healthy trees may also be attacked. Mated females bore entry holes about 2 mm in diameter into bark, their presence may be detected by lines if fine pale frass from the borings or, in healthy trees, narrow flows of sap. Young trees are often selected and sometimes females will attack narrow branches or twigs, in which case they bore an entrance hole just beneath the base of a bud. The presence of Anisandrus is often an indicator of stressed trees, and the species is usually a secondary pest, attacking trees that are already weakened by infestations of other scolytids. Oviposition galleries extend several centimetres into the xylem, they are sometimes forked and eggs are placed loosely along the length. Larvae feed on the fungus developing on the walls, they develop rapidly and pupate in situ during the summer to produce new generation adults from July or August. So far as is known the species is univoltine throughout the range. Despite being very local and scarce in northern regions, the species if usually abundant where it occurs, adults are can be common in flight interception traps in the spring and they are strongly attracted to ethanol and ethanol/terpene baited traps.
Males 1.8-2.1 mm, females 3.2-3.6 mm. Sexually dimorphic; females with elongate elytra and raised and strongly convex pronotum, males with quadrate to slightly transverse elytra and pronotum evenly convex and not raised. Body black to brown (females usually darker), often with the forebody darker, dorsal surface with scattered pale pubescence, appendages pale brown to yellow. Head completely concealed from above, vertex evenly convex, clypeus and frons flat. Antennal club flat and broadly oval. Pronotum appearing evenly rounded from above, more strongly so in females, surface strongly asperate anteriorly, rather finely and sparsely punctured towards the base, basal margin straight and not bordered. Front coxae contiguous. Scutellum elongate and triangular. Elytra with complete and strongly punctured striae and extremely finely punctured interstices which are flat dorsally but appear convex along the declivity where the striae become impressed. Front tibiae expanded from the base and obliquely truncate apically, external margin with toothed towards the apex and inner angle with a strong hooked tooth, Middle and hind tibiae expanded from the base and curved externally to an acute apex, external margin finely toothed towards the apex. Tarsi 5-segmented and slender; second and third segments about equal in width, fourth segment diminutive and the terminal segment long and curved.