Perapion hydrolapathi (Marsham, 1802)

Perapion violaceum (Kirby, 1808)








POLYPHAGA Emery, 1886

CURCULIONOIDEA Latreille, 1802

BRENTIDAE Billberg, 1820

APIONINAE Schönherr, 1823

APIONINI Schönherr, 1823

APLEMONINA Kissinger, 1968

Perapion Wagner, 1907

These two small, metallic brentids are common and widespread and both may occur in numbers on the same plant. They are very similar in appearance, differing very subtly in the shape and relative proportions of the head, pronotum and rostrum but they may be distinguished by the form of the metasternum; in violaceum it is strongly and rather densely punctured while in hydrolapathi the punctation is sparse and very fine, this character is readily appreciated with a little practice even in the field (see below). Adults are common over a long season from early spring and are easy to find on the underside of leaves and low down on stems while larvae mine within stems, leaves and roots and occasionally induce gall formation.

Perapion hydrolapathi (Marsham, 1802)

Common and often abundant, this species has a similar UK distribution to P. violaceum although it does not extend as far north into Scotland and is very seldom recorded in Northern Ireland, further afield things are very different as the present species is restricted to the western Palaearctic and occurs mostly across western and central Europe, it is present in North Africa but to the north reaches only as far as the southernmost parts of Fennoscandia where it is much less common than violaceum. Here it is generally common across Wales and England north to Nottingham and more local further north, it occurs on various species of Rumex, often in wet or permanently damp habitats, and the usual host seems to be Broad-leaved Dock (Rumex obtusifolius L.) but adults often occur on other large docks as well as hybrids and they often occur in company with the previous species. The biology is similar to that of violaceum with overwintering adults and larvae developing through the spring and summer in stem or petiole mines, pupation occurs within a chamber in the stem and new-generation adults emerge from June or July into late summer. Large populations occasionally occur and here dock stems may be found to be crammed with mines over the entire length, and the plants discoloured and wilting.

Substantially similar to the below species but on average a little smaller, 2.5-3.2mm, the head is slightly broader compared with the (narrower) pronotum and the pronotum is less strongly punctured and distinctly less curved laterally. The species are most easily distinguished by the punctation on the metasternum and the basal abdominal sternites; in the present species it is very fine and so they appear much further apart whereas in violaceum they are much stronger (wider) and so appear closer together. The sexes differ as those of violaceum; compared with the female the male has a shorter and straighter rostrum which is more densely punctured in front of the antennal insertions and there is a small internal tooth on the basal meta-tarsomere.

Perapion violaceum (Kirby, 1808)

This species is generally common across the entire Palaearctic region, extending south into North Africa and Asia Minor and north to the UK and the far north of Scandinavia, it is abundant throughout Wales and southeast and central England, more local and scattered in the West Country and the north of England, and sporadic and rare further north to Orkney and across Northern Ireland. Typical habitats include anywhere the host plants are common, parks, gardens, woodland, agricultural land and coastal dunes etc and they are often abundant on disturbed ground, they are associated with a range of Polygonaceae but in the UK the usual hosts are the larger docks, especially Broad-leaved Dock (Rumex obtusifolius L.) but occasionally Curly Dock  (R. crispus L.) and the various hybrids, adults overwinter among tussocks or under matted leaves around host plants but they are active on the underside of old leaves during mild spells and so may be recorded throughout the winter, they become active from the first warm days of spring and remain so late into the autumn. Mating occurs in spring and early summer following a period of feeding on host foliage and females lay eggs into small cavities they chew into stems. Larvae feed entirely within the stems, roots or at the base of large petioles leaving discoloured brown mines or sometimes causing galls as they go, they pass through three instars and are fully developed within six to eight weeks. Pupation occurs within a chamber excavated by the larvae in the stems etc. and adults emerge within a week or two, new generation adults appear over a long season from late spring but there is thought to be only a single generation each year. Adults are easily sampled at any time of year by searching foliage or taking litter samples from around the host plants but they are very similar to the following species and will need to be examined very carefully in the field with a good lens, see below.

2.5-3.5mm. Very distinctive due to the large size, broad and rather flat rostrum, bicoloured body and elongate-oval elytra. Forebody black or with a weak metallic blue lustre, elytra bright metallic blue or sometimes greenish, violate or coppery, and legs black or weakly metallic blue. Head with weakly convex eyes and long diverging temples, strongly and densely punctured and with a variable impression between the eyes. Rostrum finely punctured throughout, more densely so in front of the antennae insertions, in the male weakly curved and as long as the pronotum, in the female more strongly curved and a little longer than the pronotum. Antennae inserted about the middle of the rostrum, two basal segments long and broad, the second distinctly wider than the third, funicular segments progressively shorter and broader to a compact and pointed 3-segmented club. Pronotum slightly elongate and distinctly and evenly curved laterally, surface convex or slightly flattened across the disc and with a variable median longitudinal impression in the basal third, the punctures wide, shallow and well-separated. Metasternum and basal abdominal sternites strongly and quite densely punctured. Elytra slightly wider across the base than the base of the pronotum, with rounded shoulders and evenly curved laterally to a continuously-rounded apical margin, surface with well-impressed and punctured striae; the sutural stria usually abbreviated about the apex of the scutellum, interstices much broader than the striae, each with two or three rows of very fine hairs. Legs long and robust, the middle and hind tibiae produced apically into an external tooth, the front tibiae simply rounded or nearly so. Basal segment of male hind tarsi with a small internal tooth, corresponding segment in the female simple.

Metasternum structure
Perapion violaceum (Kirby, 1808)

Stronger, dense punctation.

Perapion hydrolapathi (Marsham, 1802)

Sparse, very fine punctation.

© Dave Hodges

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