Bromius (beetle)

''Bromius obscurus'', the western grape rootworm, is a species of beetle in the leaf beetle family. It is the only member of the genus ''Bromius''. The distribution of the species is holarctic; it can be found in North America, wide parts of Europe, and Asia. The species is a known pest of grape vines in Europe and western North America.

Etymology

The genus is named after Bromius, an epithet of the Greek god Dionysus.

Taxonomic history

''Bromius obscurus'' was first described as ''Chrysomela obscura'' by Carl Linnaeus in his 1758 10th edition of ''Systema Naturae''. In 1836, the genus ''Bromius'' was first established by Louis Alexandre Auguste Chevrolat in Dejean's ''Catalogue des Coléoptères'', including Linnaeus's ''Chrysomela obscura'' as well as the species ''Eumolpus hirtus'' (now in '' Trichochrysea'') and ''Cryptocephalus vitis'' (now a synonym of ''Bromius obscurus''). In 1837, William Kirby established the name ''Adoxus'' (derived from the Greek for "inglorious") as a subgenus of ''Eumolpus'', with the species ''Cryptocephalus vitis'' as the type. ''Adoxus'' was later found to be a synonym of ''Bromius'', though historically some entomologists preferred to use the name ''Adoxus'', since at the time it was thought Chevrolat's name was unavailable.

The generic name ''Bromius'' Chevrolat in Dejean, 1836 is a conserved name. It was threatened by '' Eumolpus'' in the sense used by Kugelann in Illiger, 1798, which included both ''Chrysomela obscura'' and ''Cryptocephalus vitis''. This was because Latreille had designated the latter as the type species of ''Eumolpus'' in 1810, placing ''Bromius'' as a synonym of ''Eumolpus''. An application to conserve ''Bromius'' and other names by suppressing ''Eumolpus'' Illiger, 1798 was accepted by the International Commission on Zoological Nomenclature in 2012.

Description and variations

''Bromius obscurus'' adults are generally colored black, covered with dull yellow-grey hairs. The elytra and tibiae are either black or reddish-brown. The basal four segments of the antennae are colored orange-red. The species measures 5.0–6.0 mm in body length.

A number of variations of the species have been described:
* Typical form: Elytra black, covered by whitish hairs.
* var. ''weisei'' ( Heyden, 1883): Elytra black, hairs yellowish, tibiae basally reddish brown.
* var. ''epilobii'' (Weise, 1882): Elytra and tibiae brown, hairs whitish.
* var. ''villosulus'' ( Schrank, 1781): Elytra brown, hairs yellowish.

Historically there was disagreement over whether the ''obscurus'' and ''villosulus'' variations were in fact two separate species or not, based on morphological differences as well as other factors such as habitat and range of food plants. More recently, authors variously treat them as either variations or separate subspecies of ''B. obscurus''.

The ''villosulus'' variation is superficially similar to the species '' Aoria rufotestacea'' from Korea. In 2014, it was found that virtually all the Korean specimens of ''Bromius obscurus'' were in fact ''Aoria rufotestacea.

Distribution

''B. obscurus'' is a widespread Holarctic species. In North America, it is distributed across Canada south to North Carolina in the east and California in the west. In Asia, it is one of the few eumolpine species recorded from the north of Siberia.

In the United Kingdom, the ''B. obscurus'' was historically known from a single 10 km² square on the Cheshire/Staffordshire border around the Bosley

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