TYT.LThome / Insecta · vabzdžiai / Coleoptera · vabalai / Buprestidae · blizgiavabaliai / Agrilus biguttatus · dvitaškis siaurablizgis

ajaxloader

Agrilus biguttatus · dvitaškis siaurablizgis

  • Oak Splendour Beetle, Oak Buprestid Beetle, Two-spotted Oak Borer, Oak Jewel Beetle
  • Toplettet egepragtbille, Toplettet lancetpragtbille
  • Zweipunktige Eichenprachtkäfer, Zweigefleckte Eichenprachtkäfer
  • dvitaškis siaurablizgis
  • šaurspārnu krāšņvabole, divpunktu šaurspārnkrāšņvabole
  • Eikenprachtkever
  • toflekkpraktbille
  • opiętek dwuplamy, opiętek dwuplamkowy
  • tvåfläckig praktbagge, tvåfläckig smalpraktbagge

Agrilus biguttatus is widespread throughout Europe, reaching the northern borders of southern Sweden and the UK. North Africa, and Northern Asia. The main hosts of this insect are oak species. Agrilus biguttatus has been identified as significant contributor to oak decline in Europe. While some species prefer infesting trees with smaller stem diameters or developing in branch bark, A. biguttatus larvae typically grow within the bark of the main trunk.

The adult beetle is 8 to 13 mm long. It is metallic green in color with a black or yellow cast. There is a pair of white spots on the inner edges of the elytra. The larva is a creamy white color and measures up to 43 mm in length. The first thoracic segment is enlarged. The grub is legless and has a pair of horns on its last abdominal segment. The beetles have an average lifespan of 2 months, but some may live upwards of 5 months.

Most of the text below is from now defunct site www.ukbeetles.co.uk, where it was published under a CC BY 4.0 License.

This very widespread native Palaearctic species occurs throughout Europe north to the UK and southern Fennoscandia, it also occurs across Mediterranean North Africa, the Middle-East and Asia Minor, and further east it extends through Russia to Siberia. It is regularly imported into the U.S. among wooden crates and packing materials and has become established in several areas e.g. Michigan. Here it is generally common the south of England and the midlands, becoming more scattered and local further north to Yorkshire but is absent from the West Country and Wales although it may be under-recorded as the adults are very elusive; they feed and mate high up in tree canopies and when they do descend tree-trunks, usually in bright sunlight, they move very quickly and fly readily and fast when disturbed. Over much of the European range it has increased in abundance and this seems to be the case here as well and in recent years it is thought to be at least partly responsible for the decline in oak trees in various areas. Host trees are various oaks including Quercus robur, Q. pubescens, Q. ilex, Q. suber, Q. petraea and Q. cerris and occasionally beech, Fagus sylvatica and sweet chestnut, Castanea sativa, it has also been reported from various poplars but this association is doubtful. Adults are active from May until July or, rarely, August and occur around oaks in woodland and parkland, they usually frequent mature trees but we have recorded them from dense foliage on coppiced oaks in otherwise predominantly hornbeam woodland, they are active in warm sunny spells and only descend to low levels to oviposit on trunks. Eggs are laid in batches of 5 or 6 during May and early June among thick bark on south-facing parts of trunks on old trees, typically around 80 years old, the females always choose moist living bark and will ignore areas of bark that have dried out; they are secondary pests and will choose trees, or areas of trees, that have been stressed by other factors such as defoliation or damage to the bark caused by other insects, late spring frosts, fungi or drought, and so in severe infestations Agrilus may kill the tree before it has a chance to recover. In warmer southern parts of the range the larvae develop in a single season and the species is univoltine but further north, including the UK, they overwinter twice and so the life cycle takes two years. Larvae emerge from the eggs and bore through the bark to the cambium layer where they produce undulating galleries up to 150 cm long and pass through five instars; after the first year they measure about 10 mm and when fully grown, after a year and a half, between 25 and 45 mm. Larvae continue to develop through the winter and in the spring excavate pupal chambers about 15 mm long under areas of thick bark. Freshly eclosed adults remain under the bark for a while to harden before gnawing their characteristic D-shaped emergence holes; these are larger than those produced by our other buprestids, measuring about 4 mm by 3 mm. Newly emerged adults usually fly up to the crown of the tree where they will mature and feed on parenchyma tissue of young foliage. On the continent large populations have been reported from stressed trees; 38 emergence holes per 0.5 m of bark and in a Polish study a single oak trunk some 28 m long produced more than 700 specimens. It is the larval stage which damages the tree; young larvae produce longitudinal galleries but later instars burrow transversely and may completely girdle the trunk, the first indication of their presence may be areas of dead twigs or branches higher up on the trunk or areas of foliage in otherwise dead areas of crown. Younger and more vigorous trees can repair larval damage by reactions in the bark which produce a callus and shows as dark cracks, often with a sappy efflux. Sampling adults will require very quick reflexes with an aerial net around dense foliage in hot weather or the employment of flight-interception traps, the emergence holes are distinctively large and indicate the beetle’s presence but also indicate that it is too late to use emergence traps.

​The large size and distinctively marked elytra make this species quite unmistakable among the UK fauna. 8.3-13 mm. Dorsal surface strongly sculptured and densely and often vaguely punctured; metallic green, golden-green, blue or violet, elytra each a small white spot near the suture in the apical third. Head with obvious pale pubescence, otherwise the entire insect has very short and sparse pubescence. Head transverse with large convex eyes that are continuous with the outline, vertex longitudinally grooved and frons with a wide and shallow depression. Antennae dark metallic with elongate basal segments and serrate from the fifth segment. Pronotum transverse with two median depressions and variously depressed inside the posterior angles, lateral carinae only weakly developed. Lateral margin evenly curved and basal margin very strongly sinuate. Scutellum large; parallel-sided in the basal half and strongly narrowed to a sharply acute apex. Lateral parts of the abdomen and, rarely, the anterior pronotal angles with small white spots. Elytra long and slender, parallel in the basal half and strongly narrowed to separately rounded and finely serrate apical margins. Legs entirely dark metallic. Males are distinguished by the larger eyes and narrower frons and longer and denser frontal pubescence.