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Dinoderus minutus (Fabricius, 1775)






POLYPHAGA Emery, 1886

BOSTRICHOIDEA Latreille, 1802

BOSTRICHIDAE Latreille, 1802

DINODERINAE Thomson, C.G., 1863

Dinoderus Stephens, 1830

Native to eastern parts of Asia and the Oriental region, this species is now more-or-less cosmopolitan in distribution although in temperate regions it is synanthropic and does not survive outside. It is almost always associated with bamboo (Bambusoideae) and a wide range of species have been recorded hosting the beetle, but there are also instances of various dried products such as rice, cassava and sugarcane being attacked and ruined by the species, and in China adults have been recorded from pine bark. In tropical countries it is sometimes a serious pest of commercially grown bamboo but in temperate regions it is more notorious for attacking bamboo furniture etc. indoors. There are occasional records from Europe, including the UK, but these tend to be widely dispersed and it is unlikely the species will survive except under good conditions where suitable host material is available. The biology has been fairly well studied, at least in the wild, and most of what follows is from observations made in several regions of China but probably applies equally to tropical and subtropical regions generally. The species is polyvoltine with both adults and larvae occurring year round. There are three or four generations each year with peaks in adults abundance in February, June and October although breeding otherwise occurs continuously and the generations overlap. Adults emerge from host stems during warmer spells and they tend to be mostly nocturnal, mating on the stems and dispersing by flight over long distances if necessary to find suitable host material. They are generally inactive during mild spells and oviposition may last up to four months, occurring when suitable conditions are present. The peak period is during May and June; females bore into stems and insert single eggs, they may continue ovipositing on a single plant of move between plants to do so, and some stems become very heavily infested while others may be largely ignored. Each female produces about 20 eggs and larvae emerge after about a week and so oviposition may continue on a stem while early larvae are already feeding. Larvae bore longitudinal galleries up to 20 mm long through the ground tissue and pupation occurs in situ, under good conditions they are fully grown within six weeks and the pupal stage takes about a week. Fresh adults bore out through the stems, leaving trails of dust as they go, and begin to feed and disperse. Large local populations may damage small areas in plantations but widespread damage does not occur, plant volatiles seem to direct dispersal and attacks seem to be correlated to the nutritional condition of the hosts. Certain species of bamboo are more susceptible than others and ecological factors seem to be important; plants in lowland regions are far more likely to be attacked and young plants growing in shaded damp or wet sites as well as recently-felled stems seem to be the most attractive. For these reasons it is unlikely that populations can survive indoors in temperate regions; adults may be stimulated to emerge from processed bamboo but it is unlikely that either the conditions for feeding and mating or that suitable host material will be present; heating reduces the moisture content drastically and bamboo with less than 18% moisture is usually ignored. Nonetheless the species may cause alarm indoors because adults may suddenly emerge in large numbers in response to increased temperature or humidity, they can remain in processed stems for many months without food and while they are not photophobic, they are not attracted to light and without the presence of suitable volatiles they are unlikely to disperse away from their emergence sites.

Dinoderus minutus

Dinoderus minutus

2.5-3.0 mm long, 0.9-1.5 mm wide. Elongate and more-or-less cylindrical in form, finely and randomly punctured and with fine creamy pubescence, head and pronotum shiny dark brown to black, elytra dark reddish-brown, often paler in part, appendages paler brown. Very similar to various scolytids (especially in the form of the pronotum) but readily distinguished by the form of the terminal antennal segments. Head deflexed and not visible from above, evenly convex and with a transverse furrow behind round and weakly convex eyes, mandibles sharp and produced forward. Terminal maxillary palpomere long and pointed. Antennae inserted laterally in front of the eyes, basal segment weakly enlarged, 2-8 small and transverse, 9-11 widely dilated internally, forming a loose elongate club. Pronotum from above broadest across obtuse posterior angles and narrowed to a rounded apical margin, in side view the anterior and basal margins are closely approximated, forming an obtuse angle. In lateral view the basal third or so is flat and the disc is domed. Dorsal sculpture consists of several concentric arcs of strong teeth from the anterior margin into the disc, and a finely and regularly tuberculate basal half which has a raised median line between two oblique depressions towards the basal margin. Scutellum short and widely transverse.  Elytra short and broad, about 3.5:2.5, in side view flat above with a smoothly curved declivity that is slightly reflexed towards the apex, finely and densely punctured throughout, without striae although the punctures tend to form longitudinal lines in some specimens. Legs short but robust. Tibiae long and gradually broadened from the base to a truncate apex bearing a distinct internal apical spur, outer margins with toothed throughout; these vary in size, especially on the front tibiae. Tarsi distinctly shorter than the tibiae, 5-segmented with the basal segments short and the terminal segment long and curved, all segments simple.

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