Oak Jewel-beetle

Agrilus biguttatus is widespread throughout Europe, reaching the northern borders of southern Sweden and the UK. North Africa, and Northern Asia. Adults can fly several kilometres but the species distribution is restricted by cool temperatures. Until the 1970s, these beetles were considered rare in the UK. In the mid 1990s, A. biguttatus had begun expanding from its native range in Denmark and the Netherlands. Researchers had proposed that the expansion is largely due to global warming because it tends to live in more temperate areas. The beetle inhabits many environments, including deserts, xeric shrublands, Mediterranean scrub, mixed forests, and temperate coniferous forests. It can also be transported to new areas with shipments of wood. While Agrilus biguttatus is not currently found in the United States, its introduction could pose a significant risk to US natural environments. The main hosts of this insect are oak species, including English oak (Quercus robur), sessile oak (Q. petraea), downy oak (Q. pubescens), evergreen oak (Q. ilex), cork oak (Q. suber) and turkey oak (Q. cerris). The beetle can also be found on European beech (Fagus sylvatica) and chestnut (Castanea sativa). In Europe, species such as A. sulcicollis, A. angustulus, and A. biguttatus have been identified as significant contributors to oak decline due to their development pattern. …

Beetles have a considerable impact on the decline of oak trees across Europe, a phenomenon known as acute oak decline (AOD). One of the major symptoms of AOD is the presence of black fluid seeping from cracks in the bark, which often leads to the tree's death within a few years. If given enough time without further infestation, they are likely to recover. However, A. biguttatus, considered a secondary pest to oak, poses a serious threat by invading weakened trees before they can undergo the process of recovery. Symptomatic oak trees often exhibit distinctive D-shaped exit holes from emerging A. biguttatus adults. The decline of oak trees in Europe is believed to have been exacerbated by warmer climates and drought, as those conditions are optimal for A. biguttatus growth and host invasion. Documented evidence shows Agrilus pest incidence in Germany, France, Hungary, Poland, and England, contributing significantly to the increase in tree mortalities.