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Thylodrias contractus Motschulsky, 1839






POLYPHAGA Emery, 1886

BOSTRICHOIDEA Latreille, 1802

DERMESTIDAE Latreille, 1804

TRINODINAE Casey, 1900

Thylodrias Motschulsky, 1839

Originating in temperate Asia this pest species has been widely transported across the world, it is present throughout the Holarctic region and widespread, though seldom recorded, in the Neotropical, Oriental and Australasian regions and is present sporadically throughout Africa. It was probably associated with animal nests or communities as the female is wingless and depends on others for dispersal and a constant source of food and so an association with humans is probably solely responsible for its spread. It has been recorded throughout Europe, including the UK, but only infrequently so and always under artificial conditions, it is often referred to in the literature as the tissue beetle from its habit of chewing through tissue and other packaging to access stored products and this is an indication of how cryptic the species is and how difficult it is to find among host material. The natural host material is dry animal products and fibres such as hair, silk, wool and cotton but they have been recorded from a wide range of stored products such as skins, fur, feathers and all types of natural fabrics, they have also been observed burrowing into bones to feed on dry tissue and marrow, they have developed on cooked beef liver under artificial conditions and have been associated with a range of dry museum specimens, and as with many dermestids the first sign of their presence is damaged specimens, cast skins and frass. All females are apterous and only a small proportion of males are fully winged and so females need to be introduced into collections with new material to start an infestation and for this reason they are seldom a nuisance. The duration of the life cycle varies but is usually protracted; it can last between six months and four years depending on the rate of larval development but generally lasts about a year. Eggs are laid among host material and hatch within three or four weeks, the resulting larvae develop slowly and are usually fully-grown between 242 and 388 days, they pupate in crevices near to the host material and this phase is short; adults emerging within a week or two. Larvae may roll up and display thanatosis when alarmed and have been observed to display retrogressive moulting under stressful conditions, growing smaller with each moult, they do not display sexual dimorphism and are atypical of the family in lacking long setae and an apical tuft of hairs, but the adults are very different; the male superficially resembles a small cantharid while the female resembles the larva. Females feed after emerging and when mature they emit a pheromone to attract males, this stops after mating and so each female probably mates only once. Both sexes live up to fifty days, they spend most of their time among host material or in nearby crevices, those males that can fly rarely seem to do so, and as both sexes are small and inconspicuous they are rarely encountered but they may be sampled by leaving sticky traps in secluded places.

Thylodrias contractus 1

Thylodrias contractus 1

© U.Schmidt

Thylodrias contractus 2

Thylodrias contractus 2

© U.Schmidt

Females are larger than males, between 2 and 5mm, they are entirely brown with fine pale pubescence and lack elytra but among our larviform beetles they may be distinguished by the presence of a single ocellus on the vertex of the head and by the form of the last three antennal segments which are very elongate, the pronotum is transverse, widest near rounded posterior angles and narrowed to a straight anterior margin and the legs are long and slender with long 5-segmented Tarsi. Males are 2-3 mm, elongate and soft-bodied, and pale brown with the forebody darker than the elytra. Head and pronotum densely and finely punctured, tuberculate and pubescent, the head with a prominent dorsal ocellus, antennae 10-segmented with segments 3-6 small and narrow and 7-10 very long. Pronotum broadest near the base and narrowed to a straight anterior margin, surface sculptured as the head but more strongly tuberculate towards the base, this being obvious along the lateral margin. Elytra with rounded shoulders and sinuate laterally before rounded apical margins, sutural margins diverging from the basal third to the apex, surface without striae; roughly sculptured, finely punctured and with long pale pubescence. Legs slender and very long, pubescent throughout and lacking femoral or tibial teeth or apical spurs, tarsi with five long and narrow segments. Claws smooth and without a basal tooth.

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