Psylliodes napi (Fabricius, 1792)
This species is generally common throughout Europe north to the UK and the north of Norway, extending east through western Asia, it is widespread in north-western Africa and following introductions from Europe is now established and widespread in north eastern United States and eastern Canada. Here it is common throughout England and Wales, including all the islands, and very local and scarce further north to the Scottish Highlands, in Ireland it is widespread but very local and most records are from coastal districts. Adults are present year-round; they overwinter among moss and tussocks etc. and are active over a log season from March or April, peaking in abundance during May and June, they are associated with a variety of both wild and cultivated cruciferous plants and might be expected to occur wherever these are common e.g. arable land, wasteland, woodland borders and road verges etc. Mating occurs in the spring and females lay small batches of eggs on host foliage; often on Garlic Mustard (Alliaria petiolata (M. Bieb.)), Winter Cress (Barbarea vulgaris W.T. Aiton), Bitter Cress (Cardamine L.), Sea-Kale (Crambe maritima L.) and Watercress (Nasturtium officinale W. T. Aiton) and rocket (Sisymbrium L.) as well as a wide range of crop cultivars. Larvae emerge within two weeks and mine leaves and stems, they develop rapidly and are fully-grown after about three weeks at which time they enter the soil and pupate in an earthen cell. New generation adults emerge from June and feed on foliage through the summer before overwintering. There is a single generation each year and overwintered adults breed after a period of feeding in early spring. Sampling is easiest by sweeping suitable host material and adults usually occur in numbers, sometimes being locally very abundant in late spring and early summer, they have also been recorded from flight-interception traps in the spring and autumn.
Psylliodes napi 1
Psylliodes napi 2
Psylliodes napi 3
Psylliodes napi 4
2.2-3.3 mm. Body usually dark metallic blue, rarely with a greenish or bronze overtone, legs yellow but for the black or dark blue hind femora, antennae pale from the base and gradually darkened towards the apex. Head smoothly convex and finely punctured, with large convex eyes and variously-developed but usually weakly-defined impressed lines above the anterior tubercles. Antennae 10-segmented. Pronotum transverse, broadest across the base and narrowed to a curved (from above) anterior margin, anterior calli weak and only very slightly angled posteriorly with the lateral margin, surface with moderately strong but not dense punctures and granular microsculpture which appears to form wavy lines towards the base (X50). Elytra elongate, broadest in front of the middle, with sloping shoulders and a continuously curved apical margin, with strongly punctured striae which fade towards the apex, interstices finely punctured and with very fine granular microsculpture, epipleura almost glabrous; with only scattered fine hairs towards the base. Front and middle tibiae only weakly broadened from the base, each with a short and very fine apical spur. Hind femora massively enlarged, hind tibiae almost straight externally, the hind tarsi inserted dorsally, the insertions visible in a depression with finely toothed margins. Third segment of all tarsi strongly bilobed, in males the basal segment of the front tarsi enlarged, claws toothed at the base.