Oberea oculata (Linnaeus, 1758)

This very widespread species occurs throughout the entire Palaearctic region from Portugal to the far east of Russia, China, Japan and Korea, it is widespread across North Africa and extends north into the UK and central provinces of Fennoscandia; in Europe it occurs from lowlands to middle mountain altitudes, it is generally common in the south but less so further north where it is thought to have declined in recent decades. In the UK it was formerly known from a few widely scattered records from the north of England and around London (where it was found again in 2021) but is now confined to the Cambridgeshire fens where it is very local and rare. Host plants include various willows (Salix L.), and on the continent, where it is sometimes a serious pest of willow plantations, it is also known to develop in Aspen (Populus tremula L.) Adults are active from June until September, they spend much of their time on branches and twigs, feeding on foliage and tender bark, but on hot sunny days they fly, usually about midday, in search of mates or suitable host trees but they do not visit flowers. Following a period of feeding, during which they become sexually mature, they find partners and mating occurs on twigs or foliage. Females may examine a large number of trees before finding suitable host material, this will a healthy tree with smooth bark on the branches and twigs, and here she will climb among the smaller branches to find suitable oviposition sites, usually on branches between 2 and 5 cm in diameter. Once a site is chosen she will use her mandibles to cut two shallow longitudinal incisions in the bark and unite them at one end with a deep transverse incision which penetrates the xylem, she then turns and inserts her ovipositor into the deeper incision and lay a single egg, around which over the next two weeks the bark will regenerate and form a protective cell. She will then continue feeding and looking for more oviposition sites and this behaviour will continue for several weeks. Larvae feed on phloem and callus tissue for a while before boring into the xylem, here they will produce a gallery up to 40 cm long through the centre of the branch, as it develops it will bore a hole through the gallery in order to expel frass, these occur at very regular intervals and are a sure sign of the species presence. Development takes two years; after overwintering for a second time the larva will enlarge a chamber at the middle of the gallery and pupate, this sometimes occurs very early in the year or, occasionally, during early winter, and adults are fully formed within a few weeks but they will remain in situ until the temperature increases in May or June.