Alphitobius Stephens, 1829
Alphitobius is an Old World genus of about 20 species, the majority occur in tropical Africa and of the three Palaearctic species only two are known from Europe, both are stored-product pests which have been widely transported and are now more or less cosmopolitan in distribution. In their native ranges they occur among fungi or detritus under bark or in tree hollows or are associated with decaying organic matter such as guano in caves etc., they do not consume this material directly but rather feed on associated fungi and predate other insects and their early stages. The two species known from Europe are superficially similar but easily separated using the following key:
5.5-6.0mm. Pronotum broadest towards the base and evenly curved laterally. Anterior tibiae more strongly widened apically and with a series of distinct teeth along the outer margin. Antennomeres 6-10 transverse, the loose and elongate club consisting of 6 segments. Eyes less strongly emarginate, at the narrowest at least four facets across. Prosternal process flat.
4.5-5.5mm. Pronotum broadest about the middle and sinuate before the posterior angles. Anterior tibiae narrower apically and with tiny, indistinct denticles along the outer margins. Antennomeres 7-10 transverse, the loose and elongate club consisting of 5 segments. Eyes more strongly divided, at the narrowest point only one or two facets across. Prosternal process convex.
Alphitobius diaperinus 1
Alphitobius laevigatus 1
Alphitobius diaperinus (Panzer, 1797)
Lesser Mealworm Beetle
Known mostly as a pest of a wide range of stored products and as food for exotic pets, this species is thought to be native to tropical Africa and to have moved into Europe long ago with the trade in foods etc., and from there more recently transported worldwide e.g. it has been known from North America since before 1910. It is widespread in Europe, including the UK, and occurs mostly under artificial conditions but despite its tropical origin it also survives outside and is regularly recorded from old decaying trees in open situations. Wild specimens have been recorded through the summer as far north as southern Fennoscandia and central England although it is unlikely they will become established in the long term as larvae do not develop beyond the first instar at 10°C, but under artificial conditions the species may occur anywhere and at any time. Both adults and larvae feed on a wide range of stored products that have become damp and infested with fungi, and it may be that fungi are essential for larval development as there is a positive correlation between the presence of Aspergillus and larval development, among the usual hosts are stored grains and flours, oatmeal, wheat, barley, rice, soybeans and peanuts and they have also been recorded from linseed and oilseed products, tobacco, stored drugs and skins etc. They will consume carrion and the larvae will become cannibalistic in the absence of food, they are found in huge populations among guano and detritus in caves worldwide and because they are adapted to warm and humid conditions they often become super-abundant in poultry houses where they feed directly on droppings but also consume feathers and will attack dead and dying birds, and because they will consume any kind of soft tissue they are also used to clean skeletal matter for museum displays. Adults live between three months and two years, they sometimes swarm and will sometimes be found on walls indoors but in general they are photophobic. Mating occurs after a period of feeding and females oviposit soon afterwards, they are very fecund and each may produce up to 2000 eggs although around 300 is more usual, they continue to produce eggs and oviposit over most of their life and may disperse widely while doing so. Larvae emerge after a week or so and begin to feed immediately, the development period varies between 40 and 100 days and they pass through 6 to 11 instars, depending on temperature and humidity etc, they mostly remain within the host material but are often active on the surface at night; they can run rapidly and they bore very quickly into the host material when disturbed. Mature larvae disperse, sometimes over long distances when large populations build up, to find pupation sites among packing material or in crevices in floors and walls, they construct cocoons inside pupal cells and adults may emerge within a week under good conditions. Their effect on poultry breeders is complex; they are known to introduce and spread a range of bacterial diseases and they may be very resistant to predation as they produce highly reactive benzoquinone defence chemicals, the residues of which can cause health problems in humans, but they also control a range of other pest species, more especially various diptera which also introduce and spread diseases, and when host material becomes aerated and dry through insect activity, both adults and larvae may become facultative predators. Because this is a major pest of poultry production worldwide there have been many measures, artificial and natural, implemented for their control, conversely they are bred in huge numbers for the exotic pet industry and so are readily available from pet stores or to order on line as larvae. Adults are only very rarely encountered among mould or fungi under bark in the wild but are easily reared from larvae if they are kept in small numbers with sufficient food.
5.5-6.0mm. Elongate-oval and continuous in outline, entirely black to dark brown when mature and usually rather shiny, appendages paler brown throughout. Dorsal surface punctured and microgranulate throughout. Head transverse, distinctly emarginate anteriorly and with a more or less distinct fronto-clypeal impression, eyes convex and emarginate and antennae inserted laterally under a lateral clypeal expansion. Antennae short, much shorter than the width of the pronotum, segments 6-10 widely expanded internally so that there appears to be a loose 6-segmented club. Pronotum transverse, broadest towards the base and curved to projecting anterior angles and perpendicular posterior angles, anterior margin straight, posterior margin widely and strongly bisinuate. Scutellum triangular and punctured as the pronotum. Elytra with punctured striae complete to the apex and weakly convex interstices. Legs short and robust. Femora broad and smooth. All tibiae gradually widened from a narrow base to a truncate apex, external margin with fine setae, middle and hind tibiae with short apical spurs, front tibiae produced into a sharp internal apical tooth. Tarsi 5-5-4, without bilobed segments, claws smooth, separate and without a basal tooth.
Alphitobius laevigatus (Fabricius, 1781)
Black Fungus Beetle
Like the preceding species the Black fungus-Beetle is thought to originate in tropical Africa and to have spread worldwide via Europe in historical times, it now occurs throughout the Palaearctic region though less frequently than A. diaperinus and almost always among stored products but specimens do occasionally occur among fungi and decaying detritus under bark or among garden compost etc. It is generally only rarely recorded in Europe, although outbreaks sometimes occur in food processing plants, and there are only a very few records from the wild in the UK, all from central England. The lifestyle is also similar but it seems to be far less catholic in the range of products attacked, being mostly a pest of maize, dried products, flour infested with mould and bread in processing factories, it rarely occurs in poultry processing plants but is among the beetles regularly recorded breeding among detritus in bee hives in south east Asia. Both adults and larvae thrive in damp mouldy environments, they do not feed directly on host material but rather consume mould and scavenge among detritus, they are also very active predators and will hunt for eggs and larvae of other species among stored products. The species is bred in large quantities for the exotic pet trade, the larvae usually called ‘Buffalo worms’, and it is thought to be ideal for birds and terrarium animals as full-grown larvae are larger than those of A. diaperinus, up to 15mm fully grown, and under good conditions the life cycle is short, around 45 days.
4.5-5.0mm. Elongate-oval with the pronotum and elytra separately curved laterally, entirely black to dark brown with paler brown appendages, dorsal surface moderately shiny and quite densely punctured throughout. Head broadest across large and very deeply incised eyes; these at the narrowest point only one or two facets across, anterior margin emarginate and fronto-clypeal impression well-developed, antennae inserted under a lateral expansion of the clypeus. Antennae short, about as long as the anterior pronotal margin, segments 7-10 distinctly widened so that there appears to be a gradual 5-segmented club. Pronotum transverse, broadest about the middle and curved to obtuse anterior angles and a distinctly sinuate margin in front of perpendicular posterior angles, surface depressed either side of the base and basal margin widely and strongly bisinuate. Elytra broadest behind the middle, with obtusely-angled shoulders and curved laterally to an almost continuously curved apical margin, striae impressed and punctured to the apex. Legs robust, femora smooth, tibiae gradually broadened from the base to truncate apices; middle tibiae with fine spines externally, front and hind tibiae almost smooth or with only tiny denticles externally. Tarsi 5-5-4, without dilated segments, claws smooth, free and without a basal tooth.