Magnificent Eurhins

Eurhinus festivus(?), copyright Andreas Kay.

Weevils are one of the most incredibly diverse of beetle groups, coming in an incredible array of shapes and structures, but they are not usually renowned for their bright colours. Nevertheless, in a group of this size, there is always scope for surprise: witness the image above. Eurhinus is a genus of absolutely stunning metallic-coloured weevils native to Central and South America; one species, E. magnificus, was first recorded in Florida in 2002 and has since become established there. The photo above was identified on Flickr as E. magnificus but looking over the descriptions in Casey (1922) I suspect it is more likely to be the closely related E. festivus. Eurhinus magnificus differs in having patches of red on the pronotum and elytral humeri (the 'shoulders'); see photos here, for instance.

Eurhinus species feed on vines of the Vitaceae, the grape family. Eggs are inserted into young stems where the larvae cause distinct galls as they develop. It does not look like they are known to cause significant damage to economically important species though studies on whether it can successfully attack grapes are inconclusive.

REFERENCE

Casey, T. L. 1922. Studies in the rhynchophorous subfamily Barinae of the Brazilian fauna. Memoirs on the Coleoptera 10: 1-520.

To Make a Willow Weep

Pair of spotted willow leaf beetles Chrysomela vigintipunctata, copyright P. V. Romantsov.

As noted in an earlier post, the leaf beetles of the Chrysomelidae include some very attractive representatives. The two individuals in the photo above belong to the widespread genus Chrysomela, many species of which feed on leaves of members of the tree genera Salix, the willows, and Populus, the poplars. Some species can become numerous enough on their hosts to cause extensive defoliation, and the cottonwood leaf beetle Chrysomela scripta is regarded as a serious pest of trees such as the cottonwood Populus deltoides.

Mating pair of Chrysomela populi, copyright Beentree.

Chrysomela beetles that feed on willows are able to sequester salicin from the willow's leave and use it to secrete a defensive compound of their own, salicylaldehyde. In one European species, Chrysomela lapponica, distinct populations have been identified that feed respectively on willow or birch leaves. Experimental studies have shown that the birch- and willow-feeding populations are largely reproductively isolated from each other: either their inter-fertility is reduced, or hybrid larvae that differ in feeding preference from their mother will be laid on the wrong host tree and be unable to survive. As such, the populations can be recognised as either in the process of diverging into separate species, or as already distinct cryptic species. As birch does not contain salicin, birch-feeding C. lapponica do not produce the salicylaldehyde found in willow-feeding populations, and birch-feeders fed on willow leaves are unable to utilise salicin (Kirsch et al. 2011).

Female Chrysomela lapponica ovipositing on birch leaf, copyright Juergen Gross. As well as the variation in host plant described above, members of this species also vary widely in coloration, from red and black as in the photo to entirely black in some individuals.

As willow is most likely the ancestral food type for C. lapponica, how did some populations make the change to feeding on birch despite losing a significant factor in their own defenses by doing so? One possibility that has been suggested is that the change happened not despite the loss of salicylaldehyde, but because of it (Gross et al. 2004). While the salicylaldehyde acts as an effective defense against generalist predators, some specialist predators and parasitoids of the beetles seem to be directly attracted to it, using it as a marker to track down their target. Pressure from this angle might favour the spread of a population that does not produce the alluring salicylaldehyde.

REFERENCES

Gross, J., N. E. Fatouros, S. Neuvonen & M. Hilker. 2004. The importance of specialist natural enemies for Chrysomela lapponica in pioneering a new host plant. Ecological Entomology 29: 584-593.

Kirsch, R., H. Vogel, A. Muck, K. Reichwald, J. M. Pasteels & W. Boland. 2011. Host plant shifts affect a major defense enzyme in Chrysomela lapponica. Proceedings of the National Academy of Sciences of the USA 108 (12): 4897-4901.

Bark Beetles and their Hidden Harems

Galleries dug in a grand fir Abies grandis by fir bark beetles Pityophthorus pityographus, photographed by Louis-Michel Nageleisen.

For producers of commercial timber, the above picture would not be a pretty sight. Bark beetles are named after what they feed on: they chew galleries under the bark of trees. In some species that attack otherwise healthy trees, these borings may result in stunted growth or death. The beetles may spread fungal diseases as they move from one tree to another (Dutch elm disease is one example of a well-known disease spread by bark beetles). But on the other hand, many bark beetles play a vital row in nutrient recycling, feeding on already dead and dying trees and breaking down the wood.

The fir bark beetle Pityophthorus pityographus itself, from PaDIL.

The bark beetles belong to a group called the Scolytinae. The scolytines include over 6000 species worldwide (only a relatively small percentage of which, it should be noted, are recognised as significant pests). Oddly enough, they are actually a kind of weevil. The most characteristic feature of most weevils is their elongate snouts, but in scolytines these snouts have been lost (they would probably not be ideal for burrowing through wood). The fir bark beetle belongs to a subgroup of the scolytines called the Corthylini, distinguished from other scolytines by their elytra, which lock down so that a panel on the side of the body called the metepisternum is hidden when the elytra is closed (in other scolytines, it remains at least partially visible), and by the flattened round clubs on their antennae (Wood 1986). The Corthylini are themselves divided into two subgroups, the Corthylina and the Pityophthorina. The two groups are not that easily separated by their morphological appearance, but they are very different in their ecology. The Corthylina don't live directly under the bark, but deeper in the tree amongst the xylem (the central water-conducting tissue). Corthylinans and ecologically similar beetles, known as ambrosia beetles, live in association with a fungus that grows on the xylem. The beetles, which cannot directly digest the xylem themselves, feed instead on the fungus.

The Pityophthorina, on the other hand, are true bark beetles, with most species feeding directly on the tree's phloem (the sugar-conducting tissue around the outer part of the tree). Other species in this group burrow in the tree's seeds, or feed on the pith inside slender stems. The main diversity of Pityophthorina (and of Corthylini in general) is in the Americas, particularly in cooler temperate or tropical highland environments, with over 500 known species in North and South America. Two species, Pityodendron madagascarensis and Sauroptilius sauropterus, are found in Madagascar, while the genus Mimiocurus includes ten species found in Africa and Asia. The largest genus in the Pityophthorina, Pityophthorus, includes about sixty species in Africa and Eurasia in addition to over 300 in the Americas. Wood (1986) suggested that the Eurasian species of Pityopthorus were probably descended from relatively recent migrations from North America, but African and Madagascan species of Pityophthorina may represent more basal lineages.

Female Dendroterus decipiens, photographed by T. H. Atkinson.

As well as their economic and ecological significance, scolytines have attracted attention for the range of breeding behaviours they exhibit (Kirkendall 1983). Bark beetle galleries are not just feeding structures, they are also breeding structures. Females mate and lay their eggs within the galleries, and their larvae hatch and continue to feed there. The Pityophthorina are described as including both monogynous and polygynous species, but these terms refer to the number of females in a gallery, not necessarily the mating habits of the males. In monogynous species, a gallery will be home to only a single female. Construction of this gallery may have been started by the female herself, or it may have been started by a male who was then joined by the female. In most monogynous Pityophthorina, the latter is the case (and the mating system is monogamous as well as monogynous), but the female is the one to start the gallery in the genus Conophthorus (Conophthorus species feed in pine cones, and may be restricted to monogyny by the small spaces available for gallery construction). Conopthorus males that mate with the female may not remain in the gallery, but may leave directly after mating. Males that don't stay in the gallery can mate with more females, of course, but males who do stay will be able to prevent their mate from mating with another male herself before laying her eggs. Also, by helping to maintain the gallery (or by constructing the gallery himself to begin with), the male may encourage the female to oviposit faster, or improve conditions for the larvae when they hatch.

In polygynous species, such as most Pityophthorus species, a single gallery will be home to multiple females. In most polygynous Pityophthorina, a single male will co-habit with a harem of females. A few pityophthorinans of the genus Araptus are inbreeding polygynes: males do not leave their parent gallery, but instead mate with their sisters before the latter leave the gallery. Inbreeding species seem to show remarkable control over sex ratios in the population, with many more female larvae produced than males. Interestingly, monogynous and polygynous galleries tend to differ in physical structure: monogynous galleries tend to be simple and direct, with only one or two arms extending along or across the host plant from the central nuptial chamber. Polygynous galleries, on the other hand, may have several arms radiating from the nuptial chamber, with each arm probably being built by a separate female.

REFERENCES

Kirkendall, L. R. 1983. The evolution of mating systems in bark and ambrosia beetles (Coleoptera: Scolytidae and Platypodidae). Zoological Journal of the Linnean Society 77: 293-352.

Wood, S. L. 1986. A reclassification of the genera of Scolytidae (Coleoptera). Great Basin Naturalist Memoirs 10: 1-126.

The Burlinius Head-hiders

Cryptocephalus (Burlinius) bilineatus, photographed by Josef Dvořák.

I may have to confess that, in direct opposition to the Deity, I am not overly fond of beetles. There are, quite simply, far too many of them, and even beetle families can be inordinately difficult to distinguish unless one is an expert (particularly the endless array of minute brown ones). Nevertheless, everything in beetles comes with an exception, and there are some groups that stand out: one of these is the leaf beetles of the Chrysomelidae. Chrysomelids are a highly diverse group, comparable to (though perhaps getting less press than) their close relatives the weevils and longicorns. They come in an enormous array of shapes and colours, and yet almost all (emphasis on almost) seem to carry an unmistakeable stamp saying, "I am a chrysomelid".

Cryptocephalus (Burlinius) pusillus, photographed by Amy.

The chrysomelid subgenus Burlinius of the genus Cryptocephalus includes over 120 species found across the Palaearctic region, with a single species known from the Simien Mountains of Ethiopia (Schöller 2002). The name Cryptocephalus means 'hidden head', and refers to how, when the beetle is viewed from above, the head is usually hidden underneath the pronotum. Species of Burlinius are relatively small with regular lines of punctures on the elytra, but are primarily distinguished from other Cryptocephalus species by the morphology of the male genitalia. The aedeagus (the intromittent organ) bears a dorsodistal appendage covering the dorsal opening, and two symmetrical ventral processes (Erber & Schöller 2006). The external appearance of many Burlinius species is known to be quite variable, and genital morphology is also the best way of distinguishing many species (Warchałowski 1999).

Figures from Warchałowski (1999) showing variation in elytral patterning between individuals of Cryptocephalus jocularius.

As you might have guessed from the vernacular name 'leaf beetles', chrysomelids are generally herbivorous. Host plant records for Burlinius species indicate that they are often polyphagous, feeding on a wide variety of hosts. Burlinius species have been recorded from legumes, composite-flowered plants, spurges, even pines (Erber & Schöller 2006). Cryptocephalus and related taxa belong to a subgroup of the chrysomelids called the Camptostomata, in which the females have an array of chitinous pads called the kotpresse in the rectum (Schöller 2008). The kotpresse is used to encase the eggs when they are laid in a covering made from faeces and other secretions; when the larvae hatches, it uses this covering for protection and adds to it itself as it grows.

Hazel pot beetle Cryptocephalus coryli larva in its protective case, photographed by Roger Key.

REFERENCES

Erber, D., & M. Schöller. 2006. Revision of the Cryptocephalus-species of the Canary Islands and Madeira (Insecta, Coleoptera, Chrysomelidae, Cryptocephalinae). Senckenbergiana Biologica 86 (1): 85-107.

Schöller, M. 2002. The first representative of Cryptocephalus subgen. Burlinius Lopatin from tropical Africa (Chrysomelidae: Cryptocephalinae). Genus 13 (1): 33-37.

Schöller, M. 2008. Comparative morphology of sclerites used by camptosomatan leaf beetles for formation of the extrachorion (Chrysomelidae: Cryptocephalinae, Lamprosomatinae). In: Jolivet, P., J. Santiago-Blay & M. Schmitt. Research on Chrysomelidae vol. 1, pp. 87-120. Brill: Leiden.

Warchałowski, A. 1999. Übersicht der westpaläarktischen Arten der Untergattung Burlinius Lopatin, 1965 (Coleoptera: Chrysomelidae: Cryptocephalus). Genus 10 (4): 529-627.

Weevil Ball (Taxon of the Week: Diorymerina)

Diorymerus lancifer, from Davis (2009).

The Diorymerina are a South American subtribe of the weevil subfamily Baridinae. Alonso-Zarazaga & Lyal (1999) include ten genera in the Diorymerina according to the International Weevil Community Website* (though this listing differs slightly from that given by Casey, 1922) but available info on members of the group appears to be rather sparse to almost non-existent. Which is a pity because they are certainly eye-catching animals.

*I do think it rather neat that there's an "International Weevil Community".

Baridinae as a whole are characterised by a rounded body shape but in the Diorymerina this is taken to an extreme. The dorsal profile of diorymerins is highly arched, almost circular, and at least some diorymerins have bodies nearly as deep as they are long (Casey, 1922; Davis, 2009). All members of the Diorymerina are glossy in appearance and usually such colours as black or mahogany brown though Bonomius aeneoviridis is a bright metallic green. The beak of diorymerins is usually relatively short and stout compared to other weevils.


Hiotus inflatus, from Davis (2009) again.

Lima (1956) recorded species of Diorymerina feeding on shoots and seeds of Malpighiaceae trees but other than that most species seem not to have been touched on since their original morphological descriptions, and even those are scattered and difficult to locate. Significant landmarks appear to be Casey (1922) and Hustache (1950), the latter being the first part of the rather unpleasant 'Nouveaux Barinae Sud Américains'. Most of this publication's eccentricities may perhaps be excused by its unusual publication history (Kuschel, 1983): while the original manuscript was prepared in 1929, it languished for twenty years due to lack of funding and was not published until after the author's death. Nevertheless, the four parts together add up to over three hundred pages of bare species descriptions with absolutely no illustrations, usually no explicit comparisons with previously described taxa and a whole universe of typological errors.

REFERENCES

Alonso-Zarazaga, M. A., & C. H. C. Lyal. 1999. A world catalogue of families and genera of Curculionoidea (Insecta: Coleoptera) (excepting Scolytidae and Platypodidae). Barcelona.

Casey, T. L. 1922. Studies in the rhyncophorous subfamily Barinae of the Brazilian fauna. Memoirs on the Coleoptera 10: 1-520.

Davis, S. R. 2009. Morphology of Baridinae and related groups (Coleoptera, Curculionidae). ZooKeys 10: 1-136.

Kuschel, G. 1983. New synonymies and combinations of Baridinae from the Neotropic and Nearctic regions (Coleoptera: Curculionidae). Coleopterists Bulletin 37 (1): 34-44.

Lima, A. M. da C. 1956. Insetos do Brasil vol. 10. Coleópteros. Esc. Nac. Agronomia: Rio de Janeiro.

There's Something on Your Back (Taxon of the Week: Prioninae)

The Palo Verde borer, Derobrachus hovorei, a member of the Prioninae from North America. Photo by Alex Wild.

A brief respite from Amoebozoa to present the new Taxon of the Week, the beetle subfamily Prioninae.

The Prioninae are a subgroup of the Cerambycidae, the longicorn beetles. The common name refers to the elongate, back-swept antennae that are a feature of most members of this family. Cerambycidae are a simply huge family - over 20,000 species have been described, of which about 700 belong to the Prioninae (Bílý & Mehl, 1989). The most familiar longicorns are large beetles, but longicorns come in all sizes from the very large to the very small. Larvae of most longicorns live in and feed on dead wood (females may oviposit in live wood; the process of oviposition kills off the oviposition site and rot spreads through the tree allowing the larva to feed, making some of these species serious horticultural pests), and can take as long as two years to develop. Adults, in contrast, are relatively short-lived.

The most obvious feature distinguishing Prioninae from other longicorns is the presence of a sharp lateral keel on either side of the pronotum (the anterior shield of the thorax). Prioninae are large longicorns, dark in colour and crepuscular or nocturnal in habits. Adult Prioninae probably don't feed (Willemstein, 1987), but they nevertheless possess impressive jaws with which the males engage in vicious battles to win females. The larvae are generally polyphagous (that is, they're not particularly picky over exactly what type of wood they're eating), though some exceptions occur, and oviposition by the females is usually little more complicated than pushing the eggs into already rotting wood (Bílý & Mehl, 1989).


Witchety grubs, dressed for the table. Photo by David Hancock.

Among the better-known members of the Prioninae are the witchety grubs of the genus Cnemoplites which were eaten by Australian Aborigines (Lawrence & Britton, 1991) - still are, in fact, by those who have the nous to know where to find them (I've tried them on one occasion, cooked in wood ash. To be honest, I thought they tasted a bit like snot, but the woman who had brought them assured us that they were wonderful when spread across bread in lieu of butter). The most notorious of all Prioninae, however, is probably the rather self-explanatorily named Titanus giganteus, the Titan beetle of northern Amazonia. At twenty centimetres in length, Titanus is one of the largest of all insects - technically, the Goliath beetles of the scarabaeid genus Goliathus are larger, but for some reason - probably their more compact build and less prominent mandibles - Goliath beetles don't seem quite so bowel-openingly intimidating as Titanus. Titan beetles are a rare sight even within their native range (outside Amazonia, they have only ever been recorded as specialised parasites on time-travelling comediennes) which may just be all for the best; I suspect that even an avid entomophile like myself would be hard-pressed not to go into a blind panic and start screaming like a little girl if one of those suckers started crawling up my arm.


Titanus giganteus, the largest of the Prioninae. Photo by Bruno Ramos.

David Attenborough, who is seemingly a braver man than I, did handle a specimen of Titanus giganteus on an episode of Life in the Undergrowth. In that episode, Attenborough commented on the point that the larval stage of Titanus has not yet been conclusively identified. It might seem unusual that something as doubtlessly impressive as a Titanus grub would be should go unnoticed, but when you consider the concealed habitat of the larvae, the short lives of the adults, and the extreme difficulty of identifying a holometabolous larva with its corresponding adult, this situation becomes much less surprising. The words of Francis Pascoe, commenting in 1866 on a collection of longicorns from Penang in Malaysia, are just as appropriate today as they were 140 years ago:

If we consider that the Longicorns in their perfect [i.e. adult] state are generally short-lived, and that a great majority of the species frequent particular plants or families of plants, so that only where these plants occur can we expect to find the insects, it will be readily understood how this limited range and brief existence make it almost impossible for any collector to obtain more than a portion of those that inhabit even a moderately extensive district. And thus it is that sometimes perhaps half the species of a large collection are represented each by one or two individuals only. The number of species, therefore, and the many superb novelties which Mr. Lamb has had the good fortune to capture, whilst it excites our imagination, shows us how much more might be expected if all those rich tropical lands were as thoroughly worked by entomologists as Europe has been.

REFERENCES

Bílý, S., & O. Mehl. 1989. Longhorn beetles (Coleoptera, Cerambycidae) of Fennoscandia and Denmark. Fauna Entomologica Scandinavica 22. E. J. Brill.

Lawrence, J. F., & E. B. Britton. 1991. Coleoptera. In The Insects of Australia vol. II (CSIRO, ed.) pp. 543-683. Melbourne University Press.

Pascoe, F. P. 1866. Catalogue of longicorn Coleoptera collected in the island of Penang by James Lamb, Esq. Part I. Proceedings of the Zoological Society of London 1866: 222-267.

Willemstein, S. C. 1987. An Ecological Basis for Pollination Ecology. E. J. Brill.