Aspidapion Schilsky, 1901
This small genus of very distinctive weevils includes 6 species from the Palaearctic region and 13 from the Oriental region, a further 13 species from Madagascar, Comoros, Reunion and Pamanzi are also included according to various similarities in morphology, which are also present in other African genera, and are likely to be split in the future. The European fauna includes 6 species classified among 2 subgenera. Subgenus Koestlinia Alonso-Zarazaga, 1990 includes only a single species; A. (K.) aeneum (Fabricius, 1775), which is widespread and generally common throughout the Palaearctic region including the Near East and North Africa. Subgenus Aspidapion s.str. includes 5 European species; two of which, A. soror (Rey, 1859) and A. radiolus (Marsham, 1802) are widespread and extend north to the UK, and of the others A. validum (Germar, 1817) is generally distributed across the Palaearctic region while A. acerifoliae Suppantschitsch, 1996 is endemic to the canary Islands and A. caprai Giusto, 1993 is endemic to Italy. All species are oligophagous on various Malvaceae, more especially on Alcea L., Althaea L., Lavatera L. and Malva L. Adults are active through the summer and the new generation overwinters, mating and oviposition occur in spring and summer and larvae develop in fruits, stems and roots, they pupate in situ or in the ground and all species are thought to be univoltine. They generally occur in numbers and individual plants may host hundreds of adults; they are among the few dark bodied brentids to occur on mallows and should therefore be easily sampled and identified, even in the field.
The species are small, 2-4 mm, narrow and convex, very finely pubescent and entirely black (some foreign species have reddish legs and some specimens of the common A. radiolus have paler basal antennomeres) with a metallic blue or greenish lustre. Head concave or convex and either punctured or foveate between convex and moderately prominent eyes, rostrum narrow and weakly curved, much longer in females and sometimes slightly dilated in males. Antennae inserted towards the rostral base, scape short and gradually thickened from the middle, funicular segments mostly long and narrow, club
Aspidapion aeneum 1
Aspidapion radiolus 1
Aspidapion soror 1
Aspidapion aeneum 2
Aspidapion radiolus 2
Aspidapion aeneum 3
long and pointed. Pronotum broadest near the base and narrowed to a subapical constriction and curved apical margin, base bisinuate or produced back medially, surface punctured and with a variable basal fovea. Scutellum elongate and triangular, at least 2X longer than wide, with or without basal keels (present in all UK species) and raised above the elytral surface at the apex. Elytra elongate, convex and smoothly curved laterally, widest at or slightly behind the middle and with rounded (aeneum) or sloping shoulders, striae punctured and impressed to the apex and interstices wide and flat or weakly convex. Claws toothed at the base. In males the front tibiae are curved and produced into an internal tooth at the apex, in females they are normal. Among our UK species they may be distinguished by the long scutellum which has small keels at the base, in A. aeneum these are often very weak but this species may be recognized by the deep longitudinal pit on the head between the eyes. Our species of Diplapion also have longitudinal impressions on the head, but here they are doubled and united at the base in the form of a U or V.
Our UK species can be distinguished as follows:
Head with a deep longitudinal impression between the eyes. Scutellum with at most small and weakly developed basal keels. Elytral interstices smooth appearing almost glabrous, and usually strongly metallic. 2.9-3.6 mm.
Head not longitudinally impressed between the eyes. Scutellum with two small but obvious basal keels, Elytral interstices rough, with distinct rows of pale pubescence and usually only weakly metallic.
Front tibiae produced and sharp internally at the apex.
Front tibiae normally developed
Rostrum about as long as the pronotum.
Rostrum distinctly (about 1.5X) longer than the pronotum.
Rostrum slightly narrowed in front of the antennal insertions (more strongly so in females), and shorter than the head and pronotum combined.
Rostrum distinctly narrowed in front of the antennal insertions and as long as the head and pronotum combined.
Aspidapion aeneum (Fabricius, 1775)
A widely distributed weevil occurring throughout the Palaearctic region north to southern Scandinavia. The U.K. distribution includes the southeast north to the Humber, there are very few west country records and in Wales it is coastal. This seems a little surprising as the species is generally common within its range while the host plant is common throughout the U.K. The typical habitat is disturbed ground where the foodplant grows; roadsides, field and agricultural margins and parkland etc. and it is common in urban situations. Foodplants include a range of Malvaceae; Malva alcea L. (greater musk-mallow), Malva sylvestris L. (mallow) and Alcea rosea L. (hollyhock). In the U.K. it occurs on M. sylvestris. Adults overwinter among vegetation and soil near the host and become active on the plants in April or early May depending upon the season. They may be found through the season until the autumn. During the summer a single plant may host many adults which will quickly become obvious when beaten over a tray. Larvae feed in the lower parts of the stems and the roots; they excavate long chambers in the stems where they feed and will ultimately pupate. Adults eclose in late summer and remain on the host into the autumn before overwintering.
2.9-3.6mm. Readily identified in the field, especially when found on the foodplant, by the convex-oval form and smooth, bright metallic elytra. With a lens the deep furrow on the frons and very long scutellum are obvious.
The head is convex with a broad and deep longitudinal furrow on the frons; the male rostrum is as long as the pronotum while that of the female is longer. Antennae inserted on the basal third of the rostrum; pale with a dark club. Pronotum slightly transverse; sides more or less straight and constricted behind the front angles and in front of the hind angles. Basal impression short and deep. Scutellum twice as long as wide and convex in cross section. Elytra oblong and convex; metallic green, sometimes blue or bronze. Striae well impressed and almost impunctate, the base of the first stria does not extend as far as the scutellum. Interstices much broader than the striae and flat or only weakly convex; very finely punctured and sometimes finely pubescent at the base, otherwise glabrous. Legs black to very dark brown. Male tibiae with an internal spine at the apex. Claws curved and strongly toothed at the base.
Aspidapion radiolus (Marsham, 1802)
Widespread and generally common throughout the Palaearctic region and adventive in North America (although apparently without published records), this species occurs throughout Europe from lowlands to alpine areas from the Mediterranean north to the UK, Denmark and into southern Fennoscandia, it is absent from North Africa but is represented on Madeira and the Canary Islands by ssp. chalybeipenne (Wollaston, 1854). In the UK it is generally common across southeast and central England, more local and mostly coastal in the west and Wales, including Anglesey, and very local and scarce further north to Southern Scotland. Host plants include a range of Malvaceae; in the UK mostly Common Mallow (Malva sylvestris L.) and Hollyhock (Alcea rosea L.), but more generally from other species of Malva L., including M. acerifolia (Cav.) (endemic to the Canary Islands), Tree Mallow (M. arborea (L.), Cornish Mallow (M. multiflora (Cav.), Dwarf Mallow (M. neglecta Wallr.), Least Mallow (M. parviflora L.), Small Mallow (M. pusilla Sm.) and Garden Tree-Mallow (M. thuringiaca (L.)) as well as Marsh Mallow (Althaea officinalis L.) (But apparently not in the UK). As in much of Europe this is the most common brentid on these hosts. Adults are present year-round, they overwinter among soil or litter near to host plants and are active from March or April until October, peaking in abundance during June and July. Mating has been observed over a long season from early spring and females oviposit in host stems. Larvae develop within stems and even in the thinnest of branches, they are often quoted as feeding within ovaries among developing fruits as adults have been reared from flowerheads, but these probably represent larvae that have entered the receptacle from the stem through the peduncle. Pupation occurs within stems, often towards the tips, and new-generation adults eclose during August and September; these may remain within the stems but (presumably) at least a proportion will become active as they are sometimes common on certain plants at this time. Adults are easily sampled by sweeping or beating host foliage and they often occur in large numbers.
2.7-3.1 mm. Elongate and very convex, with pale grey recumbent pubescence, shiny black and usually with a weak metallic blue or green reflection. Head strongly and closely punctured, flat or slightly concave between the eyes and without impressions although the punctures may be longitudinally confluent. Eyes large, moderately strongly convex and fringed with long grey setae. Rostrum cylindrical; slightly thickened about the antennal insertions and narrowed medially in both sexes; in females as long as the head and pronotum combined, more strongly curved and finely punctured, in males shorter, less strongly curved and more strongly punctured. Pronotum quadrate, broadest about the middle and constricted before a curved apical margin, parallel-sided or slightly broadened to acute and often produced posterior angles and straight across the base, surface strongly and shallowly punctured, distinctly microsculptured and with a variable, but usually short, longitudinal impression near the base. Scutellum elongate and pointed apically, with two prominent ridges near the base and weakly raised towards the apex. Elytra broadest about the middle and smoothly curved from rounded shoulders to a continuous apical margin with broad, well-impressed and punctured striae, the lateral striae reflexed and not visible from above, interstices wide and convex; each with two rows of very fine punctures. Middle and hind tibiae produced into a sharp external tooth, front tibiae in males curved and toothed apically, front tibiae in females slightly widened apically but not curved or toothed. Claws appendiculate.
Aspidapion soror (Rey, 1895)
Predominantly a Mediterranean species, known from France to Albania, Greece and Turkey and with scattered records from Western France into Central Europe, with the exception of the UK it is absent from the north although it was only recently recognised from the region (Morris & Péricart, 1988) and the wider distribution remains unknown. In the UK it is a very local and rare species of Southeast England and South Wales; most records are near-coastal or estuarine but, given the widespread nature of the records and the general, albeit local, distribution of the host plant, it is likely to occur more generally and almost certainly to have been confused with the very similar and generally common A. radiolus (Marsham, 1802). The host plant is Marsh Mallow (Althaea officinalis L.) and, so far as is known, the species is monophagous. This is a good guide to the present species as A. radiolus is not known to occur on Marsh Mallow (although it does on the continent). Little is known of the life-history but adults are present year-round, peaking in abundance during August and September and again, though less so, in May, and larvae are known to develop in host stems.
2.5-2.9 mm. Elongate, narrowly oval and very convex, entirely shiny black but usually with a weak metallic blue or greenish reflection, especially to the elytra, dorsal surface with very fine grey pubescence. Recognised among our fauna by the combination of distinct longitudinal keels on the base of the scutellum and appendiculate claws. General description much as A. radiolus but differing on subtle (and not always decisive) external characters. The sex will need to be determined but males are readily identified by a distinct tooth on the inner margin of the front tibial apex. In radiolus males the rostrum is about 3.2X longer than wide and distinctly longer than the pronotum; in the present species it is about 2,8X longer than wide and about as long as the pronotum. In radiolus females the rostrum is about 4.3X longer than wide and as long as the head and pronotum combined; in the present species it is about 3.7X longer than wide and usually distinctly shorter than the head and pronotum combined. These features are usually distinctive and will certainly become obvious when examining a series of each, but specimens, and especially females, can be problematic. More generally the body is a little less shiny, the rostrum tends to be more strongly curved and the pronotal punctation denser (on the disc each separated by less than a puncture width) in soror. Males can always be identified by the form of the aedeagus; in soror it is curved much more strongly before the apex (lateral view) whereas in radiolus the inner margin is smoothly curved from base to apex.