Chaetocnema concinna (Marsham, 1802)
Mangold flea beetle
This species is generally common over much of the Palaearctic region from Europe to the far east of Russia, China, Japan, Korea and Taiwan; it is widespread in Europe north to the Arctic Circle and occurs in North Africa and on most of the Mediterranean islands. The first record from North America was from Massachusetts in 1979 and since that time it has been found to be widespread in the north east and adjacent parts of Canada and it has been recorded further afield, from Texas and Oregon. In the UK it is common throughout England and Wales, including all the islands, and it occurs across southern Scotland and Northern Ireland but, apart from occasional records from the Highlands, appears to be absent further north. Adults are present year-round; they overwinter in grass tussocks or among decaying vegetation and are active from April until October, peaking in abundance during May and June. Habitats include grassland, wetland margins, arable land, woodland, dunes and beaches, saltmarshes and disturbed areas such as gardens, roadsides and allotments, but the species flies well and during the warmer months might be found in just about any situation. On the continent it has been recorded up to 2300 m. Adults have been recorded feeding on a wide range of foliage including various Polygonaceae such as Sheep’s Sorrel (Rumex acetosella L.), Common Sorrel (R. acetosa L.), Buckwheat (Fagopyrum esculentum Moench), Black Bindweed (Fallopia convolvulus (L.)) and Chinese Rhubarb (Rheum palmatum L.) and they may also be pollen feeders as they often appear in numbers on hawthorn blossom in the spring. Host plants also include a wide range of Polygonaceae but plants from ten or so families have been recorded hosting the species e.g. Fat Hen (Chenopodium album L. Amaranthaceae), orach (Atriplex L. Chenopodioideae), Lesser Periwinkle (Vinca minor L. Apocunaceae) and various beets (Beta L.) where the species is an occasional pest of commercially grown cultivars. Mating occurs after a period of feeding in the spring and oviposition begins in May and continues into July. Eggs are laid in small batches in the soil below host plants and larvae mine fine galleries in the roots, they pass through three instars and are fully developed within about four weeks. Larvae pupate among the roots from July until September and the first new-generation adults usually appear from July. There is a single generation each year. Adults can be sampled by general sweeping; they also occur on low foliage of a range of trees and will often appear in flight-interception traps. Adults produce numerous small round holes in foliage as they feed and these may be a clue as to the presence and local abundance of the species.
Chaetocnema concinna 1
Chaetocnema concinna 2
Chaetocnema concinna 3
Members of this genus are easily recognized among our UK fauna by the enlarged hind femora and broadly-toothed external margin of the middle and hind tibiae. 1.8-2.4 mm. Broadly elongate-oval and discontinuous in outline, body bronze, coppery or dark metallic green, antennae pale with darkened distal segments, legs pale with femora and tibiae and tarsi at least in part darkened. Head smoothly convex between large, convex and almost circular eyes, frontal groove strongly curved forward from the inner margin of the eyes, surface finely microsculptured throughout and with fine pale setae around the antennal tubercles. Antennae 11-segmented, long and filiform, the terminal segment, especially in males, broadly rounded, flattened internally and asymmetric; the inner margin more strongly curved than the outer margin. Pronotum transverse, broadest across acute posterior angles and evenly narrowed to slightly-projecting anterior tubercles, apical margin curved, basal margin bordered and widely sinuate, surface evenly punctured and microsculptured throughout and with a short longitudinal furrow towards each lateral margin in the basal half. Elytra broadest in the basal half, with sloping shoulders and a continuous apical margin, striae, including a scutellary striole, regular throughout (nowhere confused), interstices very finely punctured and uneven but without distinct microsculpture.