Chaetocnema hortensis (Fourcroy, 1785)

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POLYPHAGA Emery, 1886

CHRYSOMELOIDEA Latreille, 1802

CHRYSOMELIDAE Latreille, 1802

ALTICINAE Newman, 1834

Chaetocnema Stephens, 1831

Chaetocnema Stephens, 1831

This species is generally common throughout Europe from the Mediterranean north to the UK, Denmark and reaching beyond the Arctic Circle in Scandinavia; it is widespread across North Africa and extends east through Asia Minor and Russia to Eastern Siberia, China and Japan. Here it is common throughout Southern and Central England and Wales and more local and sporadic to the far north of Scotland and in eastern Ireland and, with the exception of Orkney and Shetland, it occurs on all the islands. Adults occur throughout the year; they are active over a long season from March or April until the autumn, peaking in abundance during May and June and again in September and October, and they overwinter among grass tussocks and litter and are often active in mild spells. Typical habitats are grassland, heath and moorland, woodland margins, waste ground and other disturbed places, coastal dunes, saltmarshes and wetland margins. Host plants include various wild and cultivated grasses (Poaceae); they have been recorded from species of Arrhenatherum Beauv., Agropyron Gaertn.,  Phleum L., Festuca L., Bromus Scop., Sesleria Scop., Dactylis L., Poa L., and  Wild Oat (Avena fatua L.),  adults are frequently recorded from various crop species such as Barley (Hordeum L.), Wheat (Triticum aestivum L.) and Rye (Secale cereal L.), and they occasionally feed on foliage of other species such as sedges (Cyperus L.) and Sheep’s Sorrel (Rumex acetosella L.) Adults feed on foliage, typically producing elongate holes along leaf blades, while larvae mine through lower stems and roots, and when present in large numbers they may cause economic damage to crops, especially young spring wheat and Barley. Mating occurs from early spring following a period of feeding when adults nibble the tips of freshly emerging leaves, and eggs are laid low down on stems of young plants from April. Larvae emerge after a week or two and mine lower sections of host stems; they develop rapidly and may move between plants as they grow. When fully grown they bore out of the stem at ground level and burrow down to pupate in an earthen cell. Pupation occurs during June and July, this stage lasts for about 20 days and the first new-generation adults appear from July. Adults are easily sampled by sweeping vegetation, they fly well and regularly appear in Malaise and flight-interception traps, and they sometimes come to light traps. They may be found among flood refuse or extracted from suitable tussock or litter samples during the colder months.

Chaetocnema hortensis 1

Chaetocnema hortensis 1

Chaetocnema hortensis 2

Chaetocnema hortensis 2

1.6-2.3mm. Elongate-oval and discontinuous in outline, body glabrous, entirely metallic bronze, copper or green, antennae dark distally with at least 3 basal segments pale, legs pale with darker femora which may have a weak metallic reflection. Head broadly transverse (from above), moderately strongly and more-or-less evenly punctured throughout and flat (without a median longitudinal groove) between the antennal insertions, with only a fine transverse and arcuate line (frontal groove) from near (but not reaching) the upper margins of the eyes. Pronotum transverse, broadest in the basal half and narrowed to slightly obtuse posterior angles and a rounded apical margin, surface rather strongly and densely punctured throughout, without impunctate areas or basal impressions. Elytra elongate, broadest near the middle and evenly curved from rounded and only slightly protruding shoulders to a continuous apical margin, striae confused in the basal third or half and mostly irregular (interrupted or wavy) In the apical half. Hind femora greatly enlarged, front and middle femora normal. Distinguished among our flea beetle genera by the external tooth to the middle and hind tibiae. Males have the basal segment of the front and middle tarsi enlarged.