Brassicogethes aeneus (Fabricius, 1775)
A common and widespread species throughout the Holarctic; North Africa, Europe, Asia east to Mongolia, China and the far east of Russia. Sometimes considered as a subspecies, it occurs throughout America south to northern Mexico although it is more prevalent in the western states. In the U.K. it is abundant throughout England and Wales although records are mostly coastal in the West Country and scattered through Scotland and the Western Isles. There are records scattered throughout Ireland. Locally it is abundant everywhere, the adults occurring in just about any situation. Through the spring and summer they may be seen among virtually any yellow flowers e.g. Ranunculus or Taraxacum, and tapping umbels on to a sheet will produce numbers of adults. Crucifer crops, more especially oilseed rape and mustards (Sinapis alba Linn., and Brassica juncea (Linn.)), are usually infested with huge numbers and the beetles are classed as serious pests.
Adults overwinter among vegetation or in the soil. In the spring they fly to a wide range of flowers to begin feeding on nectar and pollen. When ready to lay eggs the females fly to crucifers, here they settle on open flowers or bore into closed buds to continue feeding. Green buds are selected for egg laying; a hole is bitten through the base of the sepals and one or several eggs are inserted. Larvae hatch within a week or so, sometimes feeding between several buds, and develop within two weeks before dropping to the ground in order to pupate in the soil. The pupal stage lasts for a week or two before the adults emerge and fly to a range of flowers to begin feeding before overwintering. There is a single generation each year.
2-2.7mm. The metallic green, blue or violet colour with dark appendages will make this species obvious in the field although when overcast they may appear black and can be mistaken for other species.
Brassicogethes aeneus 1
Brassicogethes aeneus 2
Brassicogethes aeneus 3
Upper surface microsculptured, the strength of this varies and it is often absent. Head strongly contracted in front of eyes, diffusely punctured and pubescent. Eyes large and prominent. Clypeal margin straight. Thorax transverse, almost parallel sided in basal half, with sides strongly bordered and weakly explanate. Front and hind margins not bordered, hind margin weakly sinuate. Surface strongly punctured, without fovea. Scutellum curved triangular, punctured and pubescent as elytra. Elytra punctured and pubescent, without cross striations. Depressed inside weak humeral prominence but without any trace of an impressed longitudinal stria. Antennae black with segments two to six variously lighter. Basal segment rounded on inner margin. Club compact, with three broad segments. Mid and hind legs dark, front legs lighter. Mid and hind tibiae strongly broadened to apex, front tibiae much less so. Teeth on outer side of front tibiae fine, gradually increasing in size to apex. Segments two and three of front tarsi strongly bilobed. Claw segment of tarsi long and curved, claws not toothed at apex.