PLATYPODINAE Shuckard, 1839
Ambrosia Weevils
This unusual mammal inhabitats most water sources in Eastern Australia, where it is widespread and common, although elusive. UK distribution is decidedly limited.
Introduction
In 1799 George Shaw described and named a bizarre primitive mammal from the west coast of Australia. He named it Platypus anatinus (Platypus-Flat-footed, anatinus-Duck-like). It was quite quickly realized that the generic name was already used for some ambrosia beetles and so, as Johann Blumenbach had independently described the animal-from a specimen given to him by Sir Joseph Banks-and named it Ornithorhynchus paradoxus, it was reassigned to that genus and the name by which we now know it is Ornithorhynchus anatinus (Shaw, 1799). Unfortunately the original name of Platypus stuck but it should be immediately obvious to the coleopterist which of these two remarkable species is the most fascinating.
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Along with the curculionid subfamily Scolytinae these are generally known as Bark Beetles or Ambrosia Beetles. In 1836 Schmidberger observed that the larvae were not feeding on wood but on a sticky lining in the tunnels. He likened this to ‘Ambrosia’ or ‘food of the Gods.’ Hartig in 1844 recognized this to be fungal growth. A few dozen species of ambrosia fungi have been described and there are probably many more. They are thought to be dependent on transport and inoculation provided by their bark beetle symbionts as they have not been found in any other situation. Little is known about their specificity to ambrosia beetle species.
Around the World
The Platypodinae is a large subfamily of more than 1000 species, most of which occur in the tropics. Most species breed in larger diameter host materials; posts etc. and standing or felled timber. It seems likely that all species live in nutritional symbiosis with fungi and probably also bacteria. Tunnels are usually bored straight down into exposed heartwood; they are started by males which are soon joined by a single female. Pheromones produced during this activity will attract large numbers of beetles and so an attack can be severe. In general damaged wood or that devoid of bark is attacked. Mated pairs boring into the xylem introduce ectosymbiotic fungi into the tunnels upon which the adults and larvae will feed, consuming exposed mycelia and sporochidia (spore clusters). Apart from
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POLYPHAGA Emery, 1886
CURCULIONOIDEA Latreille, 1802
Platypus Herbst, 1793
P. cylindrus (Fabricius, 1792)
5-7mm
some small quantity during tunnelling, the wood is not consumed but ejected from the borings and trails of this on the wood surface soon become obvious. Larvae move freely along the adult tunnels feeding on the fungus. When fully grown each larva excavates a pupal cell off the main tunnel and the resulting adults will emerge through the original entry hole. After eclosion but before they leave the host to disperse, adults collect masses of fungal spores into specialized body surface structures called Mycangia (Greek; myco ‘fungus, angeion ‘vessel) and use these to inoculate further host material. Some species are known to steal inoculums from the fungi in other beetles’ galleries. Regarding the species of trees attacked, some species are monophagus, some are oligophagus and some are widely polyphagus. One species of Austoplatypus exhibits eusociability, one of the few non-hymenopterous insects to do so. Some species are considered as secondary pests, affecting the value of felled timber, this may become more important if tree mortality increases through climate change.
Description
Platypodinae are closely related to the Scolytinae and in general appearance are suggestive of that group but are distinguished by the elongate body form, shorter abdomen; in lateral view this is seen to be shorter than the metathorax, and first tarsal segment which is usually longer than the rest of the tarsus. The base of the pronotum is not, or only just, narrower than the base of the elytra. There is no obvious neck and the body is not waisted. Eyes finely faceted and not, or only weakly, protruding. Antennae short and apparently 6 segmented, with a conspicuous scape and 3 or 4 segmented (usually fused) club. Antennal insertions usually visible from above. Tarsi 5,5,5, and without bilobed segments. Females of all species in this family have larger maxillary palps and the gular area extends further back under the head compared to the males. Several Platypus occur in Europe but with only a single species in the U.K. it is straightforward to identify.
Platypus cylindricus (Fabricius, 1792)
This is our only U.K. member of the subfamily. It occurs throughout southern England and Wales north to the Wash and Snowdonia although it appears to be absent from Cornwall, the Isle of Wight and Man. It is of only minor importance as a forest pest; attacks usually take place in stumps but also in freshly felled trunks or logs stored in timber yards. The species is widespread across Europe and in Greece is thought to be responsible for the rapid spread of canker stain in forested areas. The usual host is oak but it has also been recorded on beech, ash, elm and sweet chestnut. They are strong fliers and are attracted to the smell of fermenting sap. Adults fly directly to cut timber without any circling or searching behaviour. Males bore into the wood and remain there until a female enters the tunnel, after which both emerge and mate on the surface. Females can be observed nocturnally on the surface of appropriate timber moving around and searching for the trails of wood dust ejected from the male burrowings. The ejected dust is white and splintery and has not passed through the beetle’s gut. After mating the female enters the tunnel first, followed by the male, and from this time it is the female who continues boring, the male moves and ejects the excavated dust. Glistening white eggs are laid in small batches of 3 or 4 in the main tunnel, starting in early autumn and continuing into winter. Larvae move along the tunnels feeding on the fungi, development may be complete in a single year or it may take two. The tunnels vary greatly; from small unbranched borings only around 8 cm in length to complex branched structures more than 2 metres long. The more developed larvae do bore to some extent, the wood dust produced being removed by the adults. Adults emerge from the wood in the summer after a short pupal stage. Ceratostomella, a species of Ascomycetes, is thought to be the main, or perhaps only, fungal symbiont.
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5-7mm. Dark to light brown but the head is usually darker. Entire upper surface with sparse yellow pubescence, this is dense around and within the elytral declivity. Head broad and steeply declined in front of a convex vertex. Vertex with a raised, longitudinal central ridge and several shallow furrows either side. Densely punctured; those toward the front longitudinally confluent, declivity with a central round or weakly longitudinal impression. Mandibles, palps and antennae pale brown or yellow. Antennal scape broad and curved on the inner side, segment 2 broad, 3-5 very small. Club single segmented and rounded. Eyes almost circular, and weakly protruding. Pronotum slightly elongate and more or less parallel, the lateral margin weakly edged, and recessed near centre. Front margin slightly sinuate, hind margin sharply produced at centre. Surface microsculptured and punctured and with a longitudinal impression toward base. Elytra parallel in the female, slightly dilated towards apex in male. Base margined and weakly raised. All striae strongly impressed and punctured, in the male they extend over the declivity, in the female the end above it. Male with a long, rounded tooth on apical curve, in the female there is, at most, only a very small tooth. Front coxae massive, prosternal process flat and sharply pointed. All femora broad and excavate on lower surface to receive the tibiae, both edges produced laterally towards apex. Tibiae short and widened towards apex. Front tibiae with 4 or 5 sharp, oblique ridges and a sharp, curved apical tooth. First tarsal segment very long and curved, 2 and 3 normal, 4 small and 5 long and curved, a little shorter than first. Claws long and weakly curved towards apex, smooth and without a basal tooth.