Aulonium trisulcus (Geoffroy in Fourcroy, 1785)      Notable A

A local southern English species; widespread in the southeast west to Dorset and North to Leicestershire (Alexander), also with records from Gloucester and Worcester (Marshall, 1978). First recorded from Enfield in Middlesex in 1904 by Pool (1904), probably from specimens introduced with elm logs imported from the continent, it then appears to have spread quickly into the home counties and north to East Anglia and Northampton. By 1937 it was recorded from Worcester, presumably from spreading through the Thames and Severn valleys or from further imported populations entering through the Bristol area. By the 1940's it may have reached the limit of its range as further records are much less frequent, and between 1964 and 1971 there were no further records so leading to speculation about its continued presence (Elton, 1971). From 1972 onwards came an abundance of records and since the 1970's it has been widespread in the south. These historical fluctuations in occurrence parallelthe incidence of Dutch Elm disease and the abundance of Scolytus beetles associated with elm; firstly from around 1921 and again from 1968.

According to several authorities A.trisulcus is a specialist predator of elm bark beetles, but it is much more likely to be saprophagous or a scavenger attracted to conditions created by Scolytus damage eg loose bark or the presence of collembola, mites or subcortical fungal growth. They may well take scolytid larvae by chance encounters but they are not obligate predators (Marshall ibid). Larvae have been found in the softer parts of the bark as well as in scolytid galleries.

Adults are active nocturnally, they fly readily and run quickly after alighting, they are well known to be attracted to MV., a factor that might further elucidate its modern distribution. They occur between May and September and have been recorded with both Scolytus scolytus and S.multistriatus. In Britain found on both common elm (Ulmus prcera and Wych elm (U.glabra), on the continent also recorded from ash (Fraxinus) with the scolytid Leperesinus fraxini (Panzer). Typical habitat is broad-leaved woodland and pasture woodland (Hyman and Parsons). Larvae have been recorded from January to July and also September, and pupae from April, June and July so it is possibly bivoltine (Marshall). The larvae is illustrated by Mrshal (Including SEMs) and by Buck (1957)

Although we include A.trisulcus only on the basis of specimens at MV in a Watford town centre garden (May and August 2007), it may well be widespread in our area as elm occurs throughout, as do several species of Scolytus including S.multistriatus.

Once familiar the adults will not be mistaken for any other species, for those unfamiliar with the species all elongate brown beetles should be examined when working bark as they might be casually overlooked for Rhizophagus spp.

4.5-7mm. Elongate and parallel sided, dull testaceous with head darker. Head densely punctured and finely reticulate, narrowed in front of eyes and with clypeal margin strongly emarginate. Widely depressed in front of eyes. Clypeus densely pubescent. Antennae inserted under side margin of head; 11 segmented with 3 segmented club. Pronotum quadrate, very finely punctate, much finer and sparser than head. Front angles weakly prodruced and lateral margins very finely bordered. With longitudinal furrows; one narrow and sharply defined close to and parallel with lateral margin, a wider and deeper pair in line with the fourth elytral striae which are joined by transverse furrows close to front and basal margin, and a pair either side medially which diverge towards base and are often incomplete. Scutellum transverse. Elytra darkened along suture, more extensively so apically, with nine complete striae and scutellary stria composed of large punctures and a deeply impressed impunctate stria from humerous to near apex outside ninth stria. Interstices flat and very finely punctate. Apices rounded. Front tibiae dilated. Mid and hind tibiae curved on inner side in male, straight in female. Tarsi 4-4-4, last segment as long as, or nearly so, the first three. Claws large and smooth, weakly toothed at base.

Two species of Aulonium are given in the Andrew Duff's checklist, A.ruficorne(Olivier, 1790) is included as a doubtfully established introduction. This species was introduced by Beare and Donisthorpe (1922) from specimens found under the bark of imported pine destined for use as pit props in the Forest of Dean. it has not been recorded since. Both specimens are keyed in Joy; ruficorne Ol. resembles trisulcus in pronotal structure and general habitus but is smaller, 3.5-4.5mm and differently coloured; black with sides of head and basal half of elytra red. Joy quotes the species associated with Ips laricis.

Description from three Watford specimens at X40

References
Buck, F.D. 1957 Mycetophagidae and Colydiidae. Proc.S.Lond.Ent.Nat.Hist.Soc. 1955:53-66
Elton, C.S. 1971. Aulonium trisulcum in Wytham woods, Berks; with remarks on its status an invader. Ent.Mon.Mag 106:190-192
Marshall, J.E. 1978. The larva of Aulonium trisulcum and its association with elm bark beetles. Ent.Gaz. 29:59-69
Pool, C.J.C. 1904. Aulonium sulcatum (trisulcus), a species of Colydiid coleoptera new to Great Britain. Ent.Rec.J.Var. 16:310




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