PHALACRIDAE | uk beetles

POLYPHAGA Emery, 1886

CUCUJOIDEA Latreille, 1802

1.5-3.5mm

PHALACRIDAE Leach, 1815

Shining Flower Beetles

These convex and tiny beetles will soon be found by observing a variety of flowers, and with experience will become familiar and distinctive.

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Around the World

This is a large family of more than 650 described species included in 2 subfamilies and about 50 genera. Many more specimens await description and this makes identification of species outside of Europe and North America very difficult. The greatest diversity is in the Old World tropical regions; 122 species in 12 genera occur in North America, 8 in Canada and about 60 in Europe. They appear to be absent from many of the Pacific islands as well as Chile. Only a single species, the invasive Phalacrus uniformis (Blackburn, 1980), is known from New Zealand. The species are morphologically well-defined and, despite their small size, soon become very distinctive. The vast majority are <4mm in length while a few tropical species just exceed 5mm. Most are rather drab coloured although there are exceptions e.g. members of the Nearctic genus Acylomus Sharp, 1888 have a pattern of pale macula and resemble certain Coccinellids. Many species are metallic. The subfamily Phaenocephalinae Matthews, 1899, originally classed as a separate family, contains only two species of Phaenocephalus Wollaston, 1873 occurring in Japan and Vietnam. In appearance they are typical of the family but here the tarsi are four segmented. The remaining species of the family are included within the Phalacrinae Leach, 1815.

Description

They are convex and oval or broadly elongate with the pronotum and elytra broadest at the base and the underside flat. The front coxae are large and round or oval, the middle coxae separated by a broad and rounded mesosternal process and the hind coxae transverse and almost continuous. The front coxal cavities are open at the base. Most are glabrous and shiny with the upper surface variously punctured and microsculptured although this tends to be weak or only poorly developed. The head is usually transverse and retracted into the thorax at least to

some degree, with eyes that are weakly convex and usually follow the outline, the temples generally well-developed but usually mostly hidden. The antennae are usually long with the two basal segments enlarged and the three terminal segments form an elongate and flattened club, the morphology of which is often useful in identification. They are inserted into cavities in front of the eyes. In outline the pronotum and elytra usually form a continuous curve, both are very convex and lack any explanate margins. The elytra bear various incomplete striae, generally only one or two near the suture towards the apex, and there may be traces of others. It seems that most species are fully winged. The legs are short and robust with the tibiae generally bearing many small spines. Tarsi usually 5-5-5; segments two and three lobed, four tiny and the terminal segment long. Claws smooth but toothed at the base.

Both adults and larvae of many species feed on fungal spores and hyphae including Ascomycetes, ergot and smut or rust fungi. The adults of some feed on pollen while the larvae consume fluids within flower heads.

Olibrus Erichson, 1845

This is the largest genus of the phalacridae with about 130 described species but the group is in need of revision and many Oriental members may eventually be transferred. With the exception of the New World Tropics the genus has a worldwide distribution; about 30 species occur in the Nearctic region and more than 30 in Europe. Unlike most phalacrids the larvae develop within the flower heads of various asteraceae and many species are thought to be host specific. Larvae feed upon liquids while the adults consume pollen. They are small beetles, 1-4mm, oval or elongate-oval and convex with the ventral surface flat. The upper surface is smooth and shiny, generally drab-coloured and lighter towards the apex, or sometimes entirely pale. Many species are to some degree metallic. The antennae are 11-segmented with a 3-segmented club, the terminal segment is sinuate laterally and this is diagnostic for the genus. The maxillary palpi are much shorter than the antennae. Pronotum widest at the base and evenly curved to the anterior margin, the basal margin is sinuate. The scutellum is triangular and large, always obvious from above. The prosternum is glabrous centrally or with very fine setae; the process lacks projections or terminal setae and the lateral margins are smoothly convex or weakly angled. The meso-ventral plates completely divide the mesosternum. In the male the third abdominal ventrite lacks a central tubercle and the terminal ventrite is not depressed. The elytra bear 1-3 variously impressed striae adjacent to the suture and the surface is sometimes very finely punctured and/or microsculptured but never with transverse impressions. Tarsi 5-5-5 except that in some foreign species the males are 5-5-4. The pro-tibiae have small apical spurs.

Phalacrus Paykull, 1800

A large genus of more than 100 species and with an almost worldwide distribution; in the New World from Alaska to Argentina, and first recorded from New Zealand in 1980. The appropriately named P. darwini Waterhouse, 1877 occurs in the Galapagos Islands. All are associated with smut fungi (Ustilaginales) or rust fungi (Pocciniales) upon which they have become specialist feeders. Many are known to overwinter as adults, generally among grass tussocks etc. They are small beetles, 1.4-4.5mm in length, entirely black or dark brown in colour and convex-oval in form. The head is transverse and widest across the eyes with the clypeus rounded, truncate or emarginate. The maxillary palps are much shorter than the antennae. The eyes are only weakly, or not at all, emarginate above the antennal insertions. Antennae vary from rather weakly clubbed to having all the segments gradually and weakly expanded towards the apex, in some exotic species the antennae are very long with each segment being long and gradually expanded apically. The terminal segment is often longer than the others. In outline the pronotum and elytra are continuous; the pronotum being transverse, widest at the base and evenly rounded. The Prosternal process lacks any terminal projection or setae. Some species are densely pubescent beneath. Scutellum large and conspicuous. Each elytron has only a single sutural stria which is usually more developed towards the apex; in some exotic species it is missing. The legs are short with the femora hidden from above, the tibiae are broad and have small apical spines; the pro-tibiae are often furnished with a series of short setae laterally towards the apex which can be useful in identification. Tarsi 5-5-5; segments 2 and 3 bilobed, at least to some extent, and often strongly so on the pro-tarsi. In the male the last abdominal ventrite lacks any median depression.

Stilbus Seidlitz, 1872

A large genus of more than 70 species with a worldwide distribution: more than half occur in the Nearctic region with about 30 in North America. Members tend to be distinctively bicoloured with a dark body and paler apical region. Adults generally inhabit grassland or flowers in a wide variety of habitats. All are small, 1.0-2.5mm, convex and oval or elongate oval with relatively long appendages. The head is generally mostly hidden within the thorax; broadest across the eyes and smooth, any punctures or microsculpture only visible at high power. The eyes are emarginate above the antennal insertion and, at most, only weakly sinuate posteriorly, they lack any posterior extension. The clypeus is (usually) arcuate but sometimes truncate. The mandibles are bidentate at the apex. The antennae are 11-segmented with a usually well-defined 3-segmented club; the terminal segment is smoothly rounded and lacking any lateral sinuation. Maxillary palps much shorter than the antennae. The pronotum is broadest at the base and smoothly rounded to the often weakly projecting front angles. The Prosternal process has a pair of stiff setae at the apex but lacks any apical projection; when viewed laterally it is right angled or narrowed beyond the procoxae. Mesosternal plate complete, dividing the mesosternum which is depressed or absent posteriorly. Scutellum equilateral and relatively small. Elytra with a single sutural stria which is usually deepened and broadened towards the apex. There are often traces of other striae, faint longitudinal depressions or rows of fine punctures which are only a little larger than the very fine and random background punctation. The surface is variously punctured and microsculptured but never transversely striate or rugose. Legs relatively long, at least within the family. Femora generally hidden by the pronotum and elytra, tibiae moderately broad, weakly sinuate and only slightly widened towards the apex, each with 2 small terminal spurs. Tarsi 5-5-5; first segment small, second elongate on the meso-and metatarsi and bilobed on the protarsi, third bilobed; broadly so on the protarsi, deeply but narrowly on the meso- and metatarsi, fourth tiny and often difficult to see within the lobes of the third, fifth elongate. Claws smooth and strongly toothed at the base.

UK Species

In the U.K. the family is represented by three genera and 16 species although the list includes Stilbus atomarius (Linnaeus, 1767), last recorded in 1946 and possibly now extinct, and Olibrus norvegicus Munster, 1901 recorded for the first time from Kent in 2012. The following description applies to our U.K. fauna. Elytra variously striate but always with one or two well impressed and incomplete sutural striae which are deepened towards the apex. Interstices microscopically punctured in most species. All our species are macropterous and at least some fly readily. Legs short; femora usually not visible in set specimens, protibiae with distinct terminal spines, the number and arrangement of which is sometimes diagnostic. Tarsi 5-5-5, segments two and three bilobed, and four very small so that they appear four segmented. Most species are black or brown although some species of Stilbus Seidlitz, 1872 are lighter red, brown or yellow towards the apex. Some specimens of Olibrus Erichson, 1845 are distinctly metallic. Identification to the generic level is straightforward but, because of the sometimes wide morphological variation, identification at the specific level may rely on an examination of the genitalia. Distinguishing the sexes on external morphology is often not possible but in some species the male may possess a more dilated second pro-tarsal segment, a distinctive terminal antennal segment or an emarginate anterior clypeal margin. Microsculpture will sometimes need to be examined but a magnification of at least X100 and excellent lighting will be needed.

Many of our species are widespread and common across the south of England and may be found by general sweeping. Examining flowers, especially yellow flowers, from late May or June onwards may produce them, often in numbers and generally among other beetles e.g. Meligethes sp. Many specimens will turn up by shaking flowers into bags or over a tray, the beetles often lay buried deep within the inflorescence and so flowers that seem devoid of specimens may give good results. After a while they become instantly recognisable, even in the field. Specimens occasionally come to u.v. light.