Of Lions and Lace

The "non-green, green lacewing" (Catanach, 2007) Abachrysa eureka. Photo by M. C. Thomas.

There is a term that bird-spotters use to describe the ability to recognise what species a bird belongs to even if one cannot see the details of its features - they refer to the "jizz" of a bird, derived from the acronym GIS for "general impression and shape". The jizz of a bird species is not something that can be described easily, if at all - it is something that can really only be appreciated with experience. It should hardly come as a surprise that the same concept applies with identifying other organisms just as much as birds. Lacewings (Neuroptera) are a smallish order of insects (only about 5000 species) that include a diversity of forms, but many look at first glance not unlike small dragonflies. Still, a closer look will reveal significant differences to a dragonfly. For a start, lacewings have longer antennae and are able to fold their wings back over their abdomen in a way that no dragonfly can. There is also the feature that gives them their name - the wings of lacewings are particularly densely covered with veins, the little criss-crossing fluid-carrying lines that you can see on any insect wing. While you might need to look very closely indeed to see the individual veins, the cumulative effect of the dense veins is to give lacewing wings a distinctive shimmer, like light off satin, or the glimmer of colour across oil. This week's highlight taxon is a specific group of lacewings - the tribe Belonopterygini.

Lacewings have a complete metamorphosis, meaning they have a distinct larval stage separated by a dormant pupal stage from a very different-looking adult. Most lacewings start out life as formidable predators, and are quite recognisable by their large, protruding jaws. The most famous are the antlions of the family Myrmeleontidae, which dig themselves conical pits at the bottom of which they lie dug into the soil, waiting for any small insects unlucky enough to fall into the pit. While the large jaws are used for capturing and macerating prey, lacewing larvae are actually liquid feeders, injecting digestive saliva into their prey then sucking out the dissolved juices (Canard, 2007). One intriguing (yet kind of disgusting) feature of the order is that the midgut is not actually connected to the hindgut until pupation, meaning that the larva is not capable of defecation. Any indigestible waste products are stored in the gut until the lacewing reaches adulthood and passed after emerging from the pupa. Can you imagine the relief?


The belonopterygin Italochrysa insignis. This photo illustrates very well the distinctive shimmer that neuropteran wings possess in the right light and which I've found is actually one of the quickest ways to recognise an adult lacewing. Photo by Sheila.

Belonopterygini are a cosmopolitan tribe of a different family, the Chrysopidae (green lacewings), whose larvae are active hunters, many of them of economic significance as predators of plant pests such as aphids and thrips. Belonopterygin larvae are specialist associates of ant nests (Freitas & Penny, 2001), feeding on the ants therein. Unfortunately, such specialist habits make Belonopterygini one of the less-studied chrysopid groups, and I have been unable to find how the larvae evade detection by the ants. Like other chrysopids, belonopterygin larvae use small bits of soil and debris to disguise themselves, starting with the shell of the egg they hatched from (Catanach, 2007). Larvae of other chrysopids have been observed to incorporate the husks of drained prey into their trashy disguises so I would be interested to know if belonopterygins do the same, as has been described recently for assassin bugs.

Adult chrysopids may be predacious like the larvae, or they may feed on non-live food such as honeydew. Honeydew-feeding species possess diverticula in the gut that house symbiotic yeasts aiding the lacewing in digestion. Sounds produced by tapping the abdomen on the substrate are used by chrysopids in courtship, and the pattern of sounds produced may differ significantly between closely related species (New, 1991). Eggs are laid perched on the end of long silk threads.

REFERENCES

Canard, M. 2007. Natural food and feeding habits of lacewings. In Lacewings in the Crop Environment (P. McEwen, T. R. New & A. Whittington, eds.) pp. 116-129. Cambridge University Press.

Catanach, T. A. 2007. Abachrysa eureka (Banks) (Neuroptera: Chrysopidae): egg, first instar larva and biological notes. Unpublished thesis, Texas A & M University.

Freitas, S. de, & N. D. Penny. 2001. The green lacewings (Neuroptera: Chrysopidae) of Brazilian agro-ecosystems. Proceedings of the California Academy of Sciences 52: 245-395.

New, T. R. 1991. Neuroptera. In The Insects of Australia (CSIRO, ed.) pp. 525-542. Melbourne University Press.

Soft Waxy Scales

Nettle ensign scale (Orthezia urticae). Photo by Pavel Krásenský.

The Hemiptera (true bugs) are one of the definite contenders for the insect order containing the most oddballs (Coleoptera and Hymenoptera are probably their competitors). Hemiptera are well marked as a group by their specialised sucking mouthparts, but within the Hemiptera a wide range of body plans have arisen. The scale insects (Coccinea) are perhaps one of the oddest groups of all, and it is one of the scale families, the Ortheziidae, that is our current Taxon of the Week.

Scale insects get their name from the adult females, which have completely abandoned the joys of mobility and live their lives on a single spot, sucking the sap from a host plant. To protect themselves they secrete a covering of sticky wax or a hardened scale. Because of their sedentary lifestyle, indulgences such as legs or eyes are unnecessary, and have become reduced or lost. Only close inspection of the adult, or of the males or nymphs, would identify these creatures as even being insects. Those scales that are significant to humans are mostly plant pests, though some species are used to produce lacquer or the red dye known as cochineal (yep, gramophone records were once made from crushed insects).


Orthezia insignis female with crawlers emerging from the ovisac. Photo from here.

Scales of both sexes first hatch out of their eggs as highly mobile nymphs called 'crawlers', with fully developed legs and antennae (Williams, 1991). This is the dispersal phase of their life cycle - not only can they crawl around, but they are also small enough to be easily blown by the wind. Once they find a suitable host plant and moult to the next instar, scale nymphs become pretty much immobile, and lose all the paraphernalia of their youth. While females pretty much remain in this state for the rest of their life, males do things quite differently. They feed for the second and third instars, then enter a non-feeding pupal stage before emerging as the winged adult (the adult males of a few species lack wings). Adult male scales also don't feed and lack mouthparts - they will only live for a short time while they find a mate. Male scales are also one of the few groups of winged insects, in addition to Diptera (flies) and Strepsiptera, to have lost one of the pairs of wings (the first time I ever saw one, I was not yet aware of this and it confused me immensely). Because of their brief lifespan, male scales are relatively rare overall, though I get the impression that they can appear in large numbers in the right season. However, they are also of microscopic size, so are not likely to be noticed.


Male Orthezia insignis. Photo from here.

Scale insects are divided between a number of families. They are often divided into two superfamilies, the Orthezioidea (archaeococcids) and Coccoidea (neococcids) (Koteja, 2000), though other authors combine them all into the Coccoidea. However, the archaeococcids are united only by primitive characters and are assumed to be paraphyletic and ancestral to neococcids. The Ortheziidae (ensign scales) is one of the most basal of the families of Coccinea, and one of the earliest families known from the fossil record, in the Lower Cretaceous (Koteja, 2000) - however, the Coccinea fossil record is extremely poor and should be treated with caution (most female scales are distinguished by microscopic characters not usually preserved in fossils, and the great difference between males and females makes them impossible to identify with each other unless specimens are preserved in the process of mating). Characters giving away the basal position of ortheziids include the presence of abdominal spiracles in the female (lost in neococcids), and compound eyes in the male (in neococcids the compound eye has disintegrated into a row of separate simple eyes). Nymphs and adult females secrete symmetrical plates of wax on their backs, while the female also secretes a wax ovisac at the end of the abdomen in which she incubates her eggs. This is the 'ensign' referred to in the common name.

The Ortheziidae are not a particularly large family by insect standards - about 200 species are known. As with other scales, a number of species have been spread around the world along with infected host plants, and some can cause trouble as pest species.

REFERENCES

Koteja, J. 2000. Advances in the study of fossil coccids (Hemiptera: Coccinea). Polskie Pismo Entomologiczne 69: 187-218.

Williams, D. J. 1991. Superfamily Coccoidea. In The Insects of Australia, 2nd ed. vol. I pp. 457-464. Melbourne University Press.

Barklice and Booklice and Such

Psocoptera is arguably the least deservedly obscure of the obscure insect orders. They're not uncommon - there's a reasonable chance that you'll have seen one in your life. You probably squashed it without giving much thought to what it was. And yet, so obscure is this order of insects that there isn't even a good vernacular name for the group. Psocoptera are minute insects (usually only a couple of millimetres long) that generally live among bark and litter, feeding on fungi. Some wingless species can be found in houses (where you might have seen one) and feed on such delicacies as dust or the glue used in book bindings, leading to their being known as booklice. The tree-living forms are sometimes referred to as barklice in comparison to booklice. Most entomologists that I know simply refer to the group as psocids, and that's exactly what I'm going to do.

Technically speaking, 'Psocoptera' is a paraphyletic group. The Phthiraptera, the true lice*, are derived from within the psocids. At the moment, things seem to be going through a transitional phase, with many authors dropping the paraphyletic 'Psocoptera' for the name Psocodea, which refers to the total group of psocids and lice. The 'Psocoptera' are divided into three suborders, the Trogiomorpha, Psocomorpha and Troctomorpha, the Phthiraptera being properly speaking a subgroup of the last. A representative of the second group, the psocomorph Blaste (photo from TOLWeb), can be seen at the top of this post, and it's the Psocomorpha that I'm looking at today.

*And holders of what is probably the worst insect order name of all to pronounce.



With over 3500 species, the Psocomorpha are generally regarded as the largest of the psocid suborders, though the Troctomorpha could give them a run for their money once the Phthiraptera are taken into account. We should probably be careful about making definite statements about this - because of their neglected nature, new species and sometimes even families of psocids continue to appear in the literature at a respectable rate. At the moment, though, it is a psocomorph that holds the honour of being probably the only invertebrate to get its picture plastered over Tetrapod Zoology, due to the nomenclatural issues that have arisen from the similarity in names of the psocid Caecilius and the amphibian Caecilia. The photo above is the one featured in Tet Zoo, and shows an identified member of the Caeciliusidae.



Most Psocomorpha are dwellers on bark or rocks. One group, the Caeciliusoidea, inhabits living foliage. Adults may be winged or wingless - many species have both forms. Many psocids cluster as nymphs - the photo above (from here*) shows one such congregation - and spin protective webs, but this is taken to the extreme in the genus Archipsocus. Archipsocus species form large colonies, and may build webs large enough to obscure tree-trunks, as can be seen in the picture below (from here). As with Embioptera, these colonies appear to be conglomerations of convenience, and there is no real social behaviour. Like aphids, Archipsocus may go through multiple generations in a summer, and the colony will contain individuals at all stages of development, both winged and wingless forms (Mockford, 1957). Once winter arrives, the colony breaks down and disperses, the survivors diapausing until the spring when they will start new colonies.

*This page also records a fantastic common name for psocids - "bark cattle", apparently because the nymphs move like a herd when disturbed.



Molecular and morphological data are mostly in agreement that the Psocomorpha can mostly be divided between four infraorders, the Psocetae, Homilopsocidea, Epipsocetae and Caeciliusetae (Johnson & Mockford, 2003; Yoshizawa, 2002). Both studies also agreed in placing Archipsocus outside these groups, as the basalmost member of the Psocomorpha. Unfortunately, beyond the bare morphology, information about most psocid groups seems to be few and far between, and there is a great deal about the order that we have yet to know.

REFERENCES

Johnson, K. P., & E. L. Mockford. 2003. Molecular systematics of Psocomorpha (Psocoptera). Systematic Entomology 28: 409-416.

Mockford, E. L. 1957. Life history studies on some Florida insects of the genus Archipsocus (Psocoptera). Bulletin of the Florida State Museum - Biological Sciences 1 (5): 254-274.

Yoshizawa, K. 2002. Phylogeny and higher classification of suborder Psocomorpha (Insecta: Psocodea: ‘Psocoptera’). Zoological Journal of the Linnean Society 136: 371-400.

What is the Sound of One Mayfly Fossilising?

Actually, two mayflies. That is, unless they're not mayflies.

Krzeminski, W. & C. Lombardo. 2001. New fossil Ephemeroptera and Coleoptera from the Ladinian (Middle Triassic) of Canton Ticino (Switzerland). Rivista Italiana de Paleontologia e Stratigrafia 107 (1): 69-78.

The Triassic is apparently not a fantastic time, insect-wise. Fossil insects from the Triassic are fairly few and far between. Needless to say, this is really annoying, because it was probably a fairly significant time in insect evolution. The giant insects of the Palaeozoic were no more - instead, it was about this time that many of the modern insect orders stepped in to take their place (Grimaldi & Engel, 2005). This unfortunately brief paper by Krzeminski & Lombardo (2001) gives us just a couple of pieces of the puzzle, but it's debatable just what we can do with them.

First, the maybe-mayfly. Krzeminski & Lombardo described Tintorina from two specimens (unfortunately, while the name Tintorina triassica appears in the abstract, the name used in the body of the article is Tintorina meridensis - I'm not sure, but I think the latter would be the correct name). The holotype retains most of the body (the head is missing), two of the wings and a few bits of leg. The paratype is just a pair of wings and a fragment of body. Though fragmentary, this collection does not put us too badly off. A large percentage of insect fossil species are only known from the wings, and the pattern of venation therein is hence the most commonly used suite of characters for distinguishing taxa. Krzeminski & Lombardo assign Tintorina to a new family of Ephemeroptera. They cite the wing venation and the general body shape as their reason for doing so, but unfortunately do not note exactly which features of the venation they refer to. Features such as the absence of a humeral vein (a small vein near the base of the wing) indicate that, if Tintorina is related to Ephemeroptera, it must lie outside the crown group. The only author to specifically comment on Tintorina since seems to be Kluge (2004), who concurred in the overall similarity of venation with Ephemeroptera, but also noted a couple of significant differences. As a result, Kluge moved Tintorina to Pterygota incertae sedis.

Next, the beetle. Coleoptera fossils are known since the Lower Permian, but carry problems all of their own. Almost the entire early fossil record of beetles is composed of isolated elytra, which offer few diagnostic characters and which may be suspected of rampant homoplasy (Ponomarenko, 2002). While representatives of recent families or their close relatives have been described from early on, a lot of doubt must hang over the accuracy of these identifications. A classic example is the Triassic family Obrieniidae, originally identified as the earliest representatives of the weevils (Curculionoidea), but now regarded as merely convergent (Kuschel, 2003). In the case of Krzeminski & Lombardo (2001), they assign a single elytron to the genus Notocupes in the family Cupedidae. The Cupedidae survive to this day - an example of a living species (Tenomerga mucida) is shown at the top of the post in a photo from Wikipedia. Generally found in rotten wood, the are one of the few survivors of the basal (paraphyletic?) beetle suborder Archostemata, making them very interesting in understanding beetle evolution. The genus Notocupes (recently regarded as a synonym of Zygadenia by Ponomarenko, 2006) is a fossil genus known from Triassic to the Palaeocene - a really quite spectacular length of time, and, in light of the problems I've just mentioned, really worth a further look.

REFERENCES

Kluge, N. 2004. The Phylogenetic System of Ephemeroptera. Springer.

Kuschel, G. 2003. Nemonychidae, Belidae, Brentidae (Insecta: Coleoptera: Curculionoidea). Fauna of New Zealand 45.

Ponomarenko, A. G. 2002. Superorder Scarabaeidea Laicharting, 1781. Order Coleoptera Linné, 1758. The beetles. In History of Insects (A. P. Rasnitsyn & D. L. J. Quicke, eds.) pp. 164-176. Kluwer Academic Publishers: Dordrecht.

Ponomarenko, A. G. 2006. [On the types of Mesozoic archostematan beetles (Insecta, Coleoptera, Archostemata) in the Natural History Museum, London]. Paleontologicheskii Zhurnal 2006 (1): 86-94 (transl. Paleontological Journal 40 (1): 90-99).

Drosophila forever?

As I've commented before on this blog, taxonomy holds an unusual position in the biological sciences in that it fills two equally significant roles. On the one hand, it is a science in its own right, investigating the best way to describe and express the relationships between organisms. On the other hand, it supplies the means for communication between biologists in all fields. For the most part, these two aims compliment each other, but sometimes they can clash. The first aim implies continual change, as our understanding of the relationships between organisms changes and (hopefully) improves. Wheeler (2007) commented in a recent editorial that "Doing taxonomy as an independent science advances simultaneously both the aims
of taxonomy and its users", a sentiment that I agree with fully (be warned, though, that the general tone of Wheeler's editorial is fairly incendiary). To fulfil the second aim, however, a certain amount of stability is usually desired, as researchers who are not working in taxonomy may have trouble keeping up with the changes (or, for that matter, appreciating their necessity).

All of the codes of nomenclature have a central commission to regulate taxonomy - zoology has the International Commission on Zoological Nomenclature, botany has the International Association for Plant Taxonomy. One of the main roles of these commissions is to allow suspension of the usual rules in cases where their strict application would cause more trouble for communication than otherwise. In the case of zoology, applications for rulings on such cases that are submitted to the ICZN are published in the journal Bulletin on Zoological Nomenclature, allowing researchers the opportunity to comment on submissions before the Commission decides on them. One submission that appeared in the December 2007 issue of the BZN involves a case that could affect a large number of researchers in many fields - the impending revision of the fly genus Drosophila.

Drosophila is a very large genus, containing about 1500 species. However, phylogenetic studies (e. g. Robe et al., 2005) have found that Drosophila as currently defined is significantly paraphyletic with regard to a number of other genera in the family Drosophilidae. There are two options to resolve this situation. One is to sink all the smaller genera arising from Drosophila into the larger genus. However, this is not regarded as a suitable solution - not only would it leave Drosophila with over 2000 species, but it would result in over a hundred secondary homonyms (two or more species ending up with the same name as a result of change in genus assignment) that would require correction. The other option, that seems much more likely to be used, is to divide Drosophila into a number of smaller genera. The name Drosophila would then be restricted to a smaller group of species closely related to the type species.

All this would be fairly routine, except that one of the species affected happens to be one of the most widely used model organisms in genetics - the "fruit fly" Drosophila melanogaster (the inverted commas are because Drosophila isn't really a fruit fly proper, but a vinegar fly). So familiar is this species that many people simply refer to it as Drosophila without invoking the species name. One might be forgiven for expecting D. melanogaster to be the type species of Drosophila, but it's not. That honour goes to Drosophila funebris (shown at the top of the post in a photo from here). And as it happens, the two species are not that closely related. If Drosophila is divided up, the Drosophila melanogaster everyone knows and loves becomes a far less familiar Sophophora melanogaster. How will geneticists respond to the loss of their favourite organism?

To avert an apocalypse in evolutionary biology, van der Linde et al. (2007) have made a submission to the ICZN to redefine the type species of Drosophila. They suggest that that honour be given to D. melanogaster rather than D. funebris, meaning that D. melanogaster would remain forever more Drosophila. But if this is accepted, what will become of D. funebris and its close friends and relatives? Will the ICZN exalt D. melanogaster to the position of type species? Or will the geneticists just have to learn to refer to Sophophora, and like it?

REFERENCES

Linde, K. van der, G. Bächli, M. J. Toda, W.-X. Zhang, Y.-G. Hu & G. S. Spicer. 2007. Case 3407: Drosophila Fallén, 1832 (Insecta, Diptera): proposed conservation of usage. Bulletin of Zoological Nomenclature 64 (4).

Robe, L. J., V. L. S. Valente, M. Budnik & E. L. S. Loreto. 2005. Molecular phylogeny of the subgenus Drosophila (Diptera, Drosophilidae) with an emphasis on Neotropical species and groups: a nuclear versus mitochondrial gene approach. Molecular Phylogenetics and Evolution 36: 623-640.

Wheeler, Q. D. 2007. Invertebrate systematics or spineless taxonomy? Zootaxa 1668: 11-18.

A Choir of Zoraptera

I may as well wrap up this series on obscure insect orders I seem to have been doing with one of the most obscure of all - the Zoraptera (for earlier installments on obscure hexapods, see here, here, here and here). Zoraptera are inhabitants of rotting logs in tropical forests (shown above in a photo from The Papua Insects Foundation). A few species range north of the tropics in North America and Asia. Until recently, they were regarded as quite rare, but apparently they have turned out to be not uncommon in suitable habitat. Zoraptera are semi-social, living in colonies of up to a hundred or so individuals.

The name "Zoraptera" means "purely wingless" (the reason for the name should be obvious), and an alternative translation of "zoros" (the same element as in the beginning of "Zoroaster", I believe) explains the occassionally used common name for Zoraptera of "angel insects". There is absolutely no rational justification for calling Zoraptera angels, but the name is just poetic enough that I hope it catches on. It is now known that winged Zoraptera do exist, just not very often. Because rotting logs at just the right stage of decomposition are a temporary resource, zorapterans have an aphid-like life cycle, with blind, wingless individuals breeding and multiplying in their log until resources start running out, at which time winged individuals with eyes start to emerge. These winged individuals are able to leave the doomed colony and seek out a new piece of suitable habitat elsewhere. Notably, the majority of winged dispersers are female - males are quite rare. Female dispersers probably mate with males of their parent colony before dispersing.

Most authors include living species in a single genus, Zorotypus. Kukalová-Peck & Peck (1993) did establish a number of new genera, but as their classification was based on wing characters and could only be applied to a selection of recent taxa (leaving those species for which winged individuals were unknown in a Zorotypus of convenience) it has not been widely accepted. A species from Cretaceous amber has been placed in a distinct genus, Xenozorotypus, with species of the modern genus Zorotypus also known from the same time period (Engel & Grimaldi, 2002).

As I alluded to previously, the phylogenetic relationships of Zoraptera are rather obscure, to say the least. To quote Engel & Grimaldi (2002): "At one time or another Zoraptera has been considered sister to Isoptera (Boudreaux, 1979; Caudell, 1918; Crampton, 1920; Weidner, 1969, 1970), Isoptera + Blattaria (Silvestri, 1913), Paraneoptera (Hennig, 1953, 1969, 1981; Kristensen, 1975), Embiidina (Minet and Bourgoin, 1986; Engel and Grimaldi, 2000; Grimaldi, 2001), Holometabola (Rasnitsyn, 1998), Dermaptera (Carpenter and Wheeler, 1999), Dermaptera + Dictyoptera (Kukalová-Peck and Peck, 1993); basal within Thysanoptera (Karny, 1922) or Psocoptera (Karny, 1932); or unresolved within either basal Neoptera (Kristensen, 1991) or Orthoptera, Phasmida, and Embiidina (Kukalová-Peck, 1991)." At present it is pretty well-accepted that Zoraptera are somewhere within the Polyneoptera, the clade or grade including the cockroaches, crickets, etc., but getting more resolution than this is still difficult. Engel & Grimaldi (2002) favour a relationship to Embioptera, while Terry & Whiting (2005) link them to Dermaptera (earwigs). Rasnitsyn (2002) points out that the characters Engel & Grimaldi used to link Zoraptera to Embioptera are prone to homoplasy, but his own suggestion of a sister-relationship to Holometabola is poorly supported.

REFERENCES

Engel, M. S., & D. A. Grimaldi. 2002. The first Mesozoic Zoraptera (Insecta). American Museum Novitates 3362: 1-20.

Kukalová-Peck, J., & S. B. Peck. 1993. Zoraptera wing structures: Evidence for new genera and relationship with the blattoid orders (Insecta: Blattoneoptera). Systematic Entomology 18: 333–350.

Rasnitsyn, A. P. 2002. Cohors Cimiciformes Laicharting, 1781. In History of Insects (A. P. Rasnitsyn & D. L. J. Quicke, eds.) pp. 104-115. Kluwer Academic Publishers: Dordrecht.

Terry, M. D., & M. F. Whiting. 2005. Mantophasmatodea and phylogeny of the lower neopterous insects. Cladistics 21: 240-257.

A Queenage of Strepsiptera

Those of you wondering about the significance of the title to this post might want to check out the comments for last week's post on Embioptera. I noted there that a collective noun for Strepsiptera would arguably be one of the most useless concepts in the English language. In making that comment, I was referring to the fact that Strepsiptera, to the best of my knowledge, pretty never occur in noticeable groups. In fact, Strepsiptera are one of the rarest of all insect orders - so rare as to be almost mythical*. As such, their existence is not widely known by non-entomologists, and the discovery of a strepsipteran specimen is usually heralded by an unsuspecting research assistant looking down a microscope at a dish of unsorted survey specimens suddenly exclaiming, "What the f*** is that?"

*If you want a more concrete example, an ecological survey being conducted by colleagues of mine has so far collected tens of thousands of specimens - including about three strepsipterans.

Strepsiptera are endoparasites of other insects. The name means 'twisted wing', and you may also find them being called stylops*. Both sexes are parasitic as larvae, and after pupating the winged males leave the host in search of females (the picture above, from Tree of Life, shows a male Pseudoxenos leaving its wasp host. Ick). Mature males never feed, and may only survive for a few hours. The females, except for one primitive family, never leave the host, but remain in a larva-like form.

*By the way, 'stylops' is both the singular and the plural.



In the extremely unlikely event of ever seeing a strepsipteran, you can rest assured that they cannot be easily mistaken for anything else. The picture above comes from here, and shows a generalised strepsipteran male. Strepsiptera have only one pair of functional wings, with the front pair reduced to balancing organs called halteres. The only other insect order to possess halteres are Diptera (flies), but in Diptera it is the hind pair that has been altered (more on that later). The antennae are branched and antler-like. The so-called 'raspberry eye' of Strepsiptera is actually unique in the insect world, with many disjoint ocelli. It can be seen better in the photo below of Caenocholax fenyesi (by Steve Taylor, from here).



The larvae are produced viviparously by the female, and emerge from the host in large numbers (so maybe there is a use for the collective noun, after all). The first instar larvae (known as triungulins) are surprisingly advanced, with well-developed eyes and legs in order to seek out a new host. Once they have found a host and burrowed in, however, all these mod-cons are jettisoned, leaving the larva legless and grub-like. The presence of such distinct larval stages is referred to as hypermetamorphosis. At least one strepsipteran family, the Myrmecolacidae, has particularly unusual host preferences - the males are parasites of ants, while the females favour grasshopppers and crickets (Kathrithamby et al., 2003). I have not been able to find whether the sex of the larva determines the host, or whether the host determines the sex.

Phylogenetically, the Strepsiptera are arguably the second most difficult insect order - probably, only the Zoraptera can claim to have caused more problems. Still, there are two main competitors for the position of nearest strepsipteran relative. For a long time, the Strepsiptera were associated with the beetles, to the extent that some authors even suggested reducing them to a subgroup of the Coleoptera. This was mainly predicated on similarities between the triungulin larvae of Strepsiptera and certain Coleoptera families, some of which shared the Strepsiptera's branched antennae and hypermetamorphosis. However, these features are also found in other unrelated insect groups, and the chance of convergence cannot be dismissed. Molecular analyses, on the other hand, suggested a relationship between Strepsiptera and Diptera, leading to the radical suggestion by Whiting & Wheeler (1994) that the strepsipteran halteres might actually be homologous to those of Diptera, and their difference in position might be due to a homoeotic reversal switching the identities of the wing pairs! At present, it is difficult to imagine how such a thing could have happened without fatally scrambling the rest of the insect's anatomy in that area, and even if they are sister groups, the Strepsiptera and Diptera may have still evolved their respective halteres independently.

Male Stylops pacificus mating with female parasitic on bee. Photo by Edward Ross, from Tree of Life.

And why should a collection of Strepsiptera be called a 'queenage'? It should be noted that parasitism by Strepsiptera (known as stylopisation), despite the inherent ickiness of having a grub-like parasite protruding from your abdomen, is rarely fatal, and males and larvae can emerge without harming the host. Indeed, stylopised hosts may live longer than they would normally. However, stylopisation can have other significant consequences. Gonad development is reduced, and stylopised hosts may often be sterile. Stylopisation may also have a dramatic effect on secondary sexual characteristics of the host - stylopised individuals may lose their expected secondary sexual features and develop features characteristic of the other sex (Salt, 1927). Hughes et al. (2004) discovered that stylopised individuals of one species of wasp did not work in the colony as normal, but abandoned the colony and formed loose aggregations elsewhere.

Parasite-induced castration is not uncommon in invertebrates, and it is believed that it is advantageous for the parasite to sterilise its host because then time and energy that the host would otherwise waste on finding and winning a mate and producing offspring can instead be focused on feeding the host and hence the parasite (think about the behavioural differences between a neutered and entire cat). Colony desertion by stylopised wasps is probably also induced by the parasite (stylopised individuals were not driven away from the colony by uninfected individuals) as the chance of successful male emergence and mating was greater in the aggregations than within the nest, where healthy wasps would destroy any male strepsipterans they spotted.

REFERENCES

Hughes, D. P., J. Kathirithamby, S. Turillazzi & L Beani. 2004. Social wasps desert the colony and aggregate outside if parasitized: parasite manipulation? Behavioral Ecology 15 (6): 1037-1043.

Kathirithamby, J., L. D. Ross & J. C. Johnston. 2003. Masquerading as self? Endoparasitic Strepsiptera (Insecta) enclose themselves in host-derived epidermal bag. Proceedings of the National Academy of Sciences of the USA 100 (13): 7655-7659.

Salt, G. 1927. The effects of stylopization on aculeate Hymenoptera. Journal of Experimental Zoology 48: 223-331.

Whiting, M. F., & W. C. Wheeler. 1994. Insect homeotic transformation. Nature 368: 696.

A Seclusion of Embioptera

A work colleague and I got into a conversation a while ago about collective nouns, and of course that eventually got onto the question of making up appropriate terms for groups of animals that currently lack collective nouns. One suggestion that I came up with that I still rather like the sound of was a "seclusion of embiopterans". From now on, I urge you to use the term when discussing embiopterans.

If through some bizarre oversight you haven't regularly found yourself discussing embiopterans, then you really should be. Also known as webspinners or embiids, embiopterans are one of the definite contenders for the total of world's coolest insects. I have personally come across a specimen in the wild just once that I found clinging to a piece of bark I pulled off its tree - unfortunately, I have to admit, no-one around me quite got what I was getting so excited about.

Webspinners are small insects that live in silken galleries they build in secluded areas such as under bark or rocks (the picture above from the homepage of Janice Edgerly-Rooks shows a female webspinner peeping out of its home). There is something of an esoteric contention about what exactly the correct name for the webspinner order should be - Embioptera, Embiidina or Embiodea all can be found. I'm going to stick with Embioptera for no good reason. The name means "lively wings" and is wildly inappropriate - webspinners are not noticeably lively, and more often than not lack wings (females are invariably wingless, males can sometimes be). It has been suggested that the name refers to the flicking movement of the male wings. The wings of male webspinners have large blood sinuses developed from the veins that are pumped full of haemolymph to make the wings rigid when they fly. When the haemolymph is drained from the sinuses, the wings become limp and floppy, able to move in whatever direction is required to let the male crawl through a female's silk nest, even bending forward over the head if the male goes into reverse.

Webspinners are often referred to as semi-social and females may share inter-connected galleries. Females also show a high level of parental care. However, females will not show any care for the young of others, and social interactions between females should probably be regarded as opportunistic rather than required (Grimaldi & Engel, 2005). The female and juvenile webspinners emerge from their silken palaces at night to feed on vegetation and detritus. Adult males, on the other hand, do not feed.



The webspinner's silk glands are located along the edge of the third segment of the forelimb tarsus, which is noticeable broadened as shown in the diagram above from BugNetMAP. The German name for embiopterans, "tarsenspinner", is therefore entirely apropos. The stunning "Life in the Undergrowth" series that I've had cause to mention before included spectacular footage of a webspinner constructing its silken fortress, waving its forelimbs in front of itself in a motion that can only be described as "wax on, wax off". So impermeable is the resulting wall that the spinner must actually cut through it with its mandibles in order to drink from water drops lying on the surface if it is not to dry up completely.

Taxon of the Week: To Give Lovecraft Nightmares

After last week's fairly nominal effort at Taxon of the Week, I'm happy to report that the ecology labs are over and done with*, and I can present you with something a little more this week. Many of you will probably be aware of the existence of parasitoid** wasps - Hymenoptera that lay their eggs inside insects and other animals so that when the larvae hatch out they can devour the unfortunate host from the inside out (in some situations, you can't help but say "devour"). The most well-known examples of parasitoid wasps are the large ichneumons***, but I'll be dealing today with a different group - the micro-wasps of the Proctotrupomorpha.

*So I can stop explaining to students that their chances of having actually found a dragonfly in a pitfall trap are fairly minimal.

**Not a typo. Technically speaking, "parasitism" implies that the parasite feeds off the host without (ideally) actually killing it. "Parasitoid" Hymenoptera are referred to as such because the growth of the larva almost invariably results in the death of the host. As such, they are better described as internal predators rather than parasites. All the same, I apologise in advance for when I'm going to inevitably slip back into referring to them as parasites later on.

***Not to be confused with the mongooses also known as ichneumons. The two are easily distinguished - mongooses are much harder to fit into a collection vial.



Proctotrupomorphs are a spectacularly diverse group. The image at the top of the post from Natural History Museum shows an array of examples from only one of the component superfamilies, the Chalcidoidea. Proctotrupomorphs also include the Proctotrupoidea, Platygastroidea and Cynipoidea. Most are exceedingly small - according to the website just linked, the smallest chalcidoid (also the world's smallest insect) reaches a maximum adult size of 0.11mm. There are proctotrupomorphs with wings, there are ones without. There are species with relatively enormous 'horns' arising from the front of the abdomen that allow space for ovipositors considerably longer than the remainder of the insect (as shown above in an image from here). Most emerge from eggs or juveniles of other arthropods, but some have taken to living in galls or pollinating figs. Some are even parasitoids of other parasitic wasps. And a few are even aquatic.



A number of proctotrupomorphs exhibit what is called polyembryony. A single egg is laid within a host which then divides into a number of larvae - up to two thousand in Copidosoma floridanum. The latter species also has a remarkable characteristic in that some of the polyembryonically produced individuals, the precocious larvae, develop enlarged mandibles and seek out and destroy other larvae of the same species but from different eggs (Zhurov et al., 2004). These precocious larvae never mature and die along with the host, leaving their identical siblings (the reproductives) to emerge as adults. In another species, Encarsia formosa (shown above in a picture from Cornell University), the gift from one larva to another is even more significant, though perhaps less willing. Most E. formosa larvae are female, and develop within greenhouse white-flies. Males are much rarer, and actually have a different host - they develop as hyperparasites of the female larvae! (Askew, 1971) As with the marine fly Pontomyia, this demonstrates the dangers potentially inherent in reading morals of human society into the biology of other organisms.



In many cases, however (particularly with egg parasites), there is often no room at the inn for more than one larva - if two larvae attempt to grow within the one host, food supplies would be exhausted before either could complete development. Therefore, most parasitic wasps have measures to prevent competition within the host. As already mentioned for Copidosoma, larvae may kill each other off within the host. There are a number of cases where development of supernumerary larvae halts terminally once one has hatched out or pupated (Askew, 1971), though the mechanisms of this termination may be unclear. Some species act to prevent supernumerary oviposition from happening at all. Trissolcus basalis (image above from SARE) is a parasite of shield bug eggs. After the female has laid within an egg, she scratches the ovipositor over the cap of the egg in a figure-eight movement to leave a mark indicating that the egg has already been parasitised. As a contrast to all this, though, Tetrastichus giffardianus is an obligate superparasite of the fruit fly Dacus cucurbitae. Larvae of T. giffardianus can only avoid encapsulation* by the host if said host has already been parasitised by another wasp, the braconid Opius fletcheri.

*Encapsulation is the formation of a hard capsule around the parasite larva by the host's natural defenses, which isolates and kills the parasite.

Finally, a number of proctotrupomorphs have abandoned parasitism to become herbivores. Fig wasps are a number of families of chalcidoids that lay their eggs within fig flowers. Fig flowers are produced entirely enclosed within an immature fig, and can only be accessed by a single small hole in the fig. The female wasp crawls within the fig and lays her eggs in the flowers. The hatching larvae feed on the inside of the fig (though ovules are deep enough to escape the depredations of the larvae) before maturing. Once mature, they mate within the fig, and the males chew an exit path for the females before expiring without dispersing. The females become covered in pollen as they escape the fig (some species apparently actively collect pollen into special pockets), which they carry to the fig they will lay in. Figweb is a website with all the information on the fig-wasp interaction you could possibly want, as well as some pretty good images.

REFERENCES

Askew, R. R. 1971. Parasitic Insects. Heinemann Educational Books: London.

Zhurov, V., T. Terzin & M. Grbić. 2004. Early blastomere determines embryo proliferation and caste fate in a polyembryonic wasp. Nature 432: 764-769.

Taxon of the Week: Butterflies on Parasites

This week I've got something a little more recognisable to go on, at least in general - butterflies! I've referred to butterflies in the past as "honorary vertebrates", as they seem to be about the only group of invertebrates that receive as much attention and recognition as vertebrate groups seem to. What those of us in the know can tell you, though, is that really butterflies are just a flashy kind of moth. Specifically, today I'll be looking at butterflies of the genus Delias.

Delias, commonly known for no particular reason as 'jezebels', are found from southern and south-east Asia to the northern tip of Australia (the image above is of Delias aglaia and is from Answers.com). The bright colouration in the photo above is usually restricted to the underside of the wings, while the upper side is far plainer - most often white with black edging, as shown in the illustration below (from Wikipedia) of Delias aganippe (a notable exception in Australia is Delias aruna, which has the upper surface of the wings bright orange-yellow). Nevertheless, they appear to be among the more colourful members of the generally modest family Pieridae, which may be best known to many of you by the cabbage whites of the genus Pieris.


There are a large number of species of Delias (I couldn't be bothered actually counting them up) placed in 23 species groups. If you want to know exactly what they all are, I'd recommend looking at Les Day's exceedingly thorough site dedicated to Delias at http://www.delias-butterflies.co.uk/. The caterpillars feed on mistletoes (hence the title of this post), which makes them notable from a conservation point of view - many mistletoes are rare and/or endangered (their thick, fleshy leaves make them very attractive to browsers), and if a species of mistletoe goes extinct then its specialist herbivores go extinct as well. While most members of Pieridae lay eggs singly, Delias lay their eggs in large clusters. The caterpillars come in a range of colours, and have long white hairs - the photo here from Wikipedia of Delia eucharis caterpillars shows both the hairs and their gregarious habits. The chrysalis is brightly-coloured, usually bright yellow or orange.

Many species of Delias have seasonal varieties, with the dry-season or winter variety being darker above, or having the underside more cryptically coloured. Studies in other Pieridae have shown that rather than being genetically determined, these variations appear to be determined by the photoperiod the larva is exposed to during development, specifically during the third and fourth instars (Hoffmann, 1973). Experimental manipulation of photoperiod exposure has even been able to induce 'seasonal variation' in species that are univoltine (only one generation per year) instead of multivoltine (multiple generations per year - Shapiro, 1977).

REFERENCES

Braby, M. F. 2004. The Complete Field Guide to Butterflies of Australia. CSIRO Publishing: Collingwood (Australia).

Hoffmann, R. J. 1973. Environmental control of seasonal variation in the butterfly Colias eurytheme. I. Adaptive aspects of a photoperiodic response. Evolution 27 (3): 387-397.

Shapiro, A. M. 1977. Evidence for obligate monophenism in Reliquia santamarta, a Neotropical-alpine pierine butterfly (Lepidoptera: Pieridae). Psyche 84: 183-190.

Diversity and Distribution of Tropical Lepidoptera: a bit of cross-purposes

This is the first of the commentaries I promised yesterday. While the rest of the world seems to have become bizarrely fixated on some fossil find from some minor mammalian clade, yesterday's Nature also included two far more interesting papers on the distribution of herbivorous insects in tropical rainforests.

"Short-range endemics" is a bit of a buzzword here in Australia at the moment, referring to the pattern in a number of taxa, especially invertebrates, of large numbers of closely-related species of exceedingly restricted distributions (a study one of my supervisors recently conducted of subterranean arachnids called schizomids found that almost each individual mesa that housed schizomids housed its own individual species). The current papers could be very interesting in light of short-range endemism. They are also very interesting in light of the overall question of why the tropics are so hyperdiverse compared to higher latitudes.

As I said yesterday, the two papers differed somewhat in their conclusions (but more on that later). First off, the paper by Novotny et al. looked at diversity within a 75,000 square kilometre area of lowland rainforest in Papua New Guinea. While the area of rainforest was continuous, the Sepik River does cut through it, and some of the plant species compared had quite restricted distributions. Novotny et al. looked at Lepidoptera (caterpillars), ambrosia beetles (Scolytinae and Platypodinae) and Tephritidae (fruitflies) and compared the species found on each host plant genus investigated between eight sites. They found that there did not appear to be a significant change in species composition from one area to another - the species that were found on Ficus at one site were pretty much the same as those found on Ficus at another, over the entire area investigated. The Sepik River did not appear to be a major barrier to dispersal.

At the same time, Dyer et al. looked at average host specificity of herbivorous caterpillars at different latitudes in the Americas. They found that tropical species tend to have much higher host specificity than temperate species. This is in direct contrast to a paper Novotny et al. published last year, that found no significant difference in host specificity between taxa in Papua New Guinea and Europe. Instead, Novotny et al. attributed the increase in insect diversity in the tropics to the shear increase in number of potential host plant species.

So on the one hand we have a paper that seems to argue for wide distributions of tropical taxa, on the other we have one that argues for high host specificity (and hence, one suspects by implication, more restricted distributions). After reading through the papers, I don't think the conflict is actually that strong, as I'll explain in a moment.

Dyer et al. do offer some suggestions for why their results were different to Novotny et al.'s last year. One is that there may be actual difference between the Old World and the Americas. I just can't see that being significant - while there are some differences in which families are dominant in each hemisphere, there are many families that are present in both, and the latitudinal influences are still similar in each - far north it's still colder. The other factor that I think is far more likely to be significant is that Dyer et al. looked at a far greater range of host species than Novotny et al - the latter looked at 18 species in each area, while Dyer et al. looked at up to a maximum of 281 species in Costa Rica. Most significant of all, though, is that Dyer et al. looked at only one potential host species per genus per area. This would tend to bias their results towards higher measurements of host specificity, but is arguably more informative. If you compare a tropical species that feeds on three species of Ficus to a temperate species that is recorded feeding on one species each of Euphorbia, Quercus and Fagus, the temperate species should obviously be regarded as far less host-specific in light of the far greater phylogenetic distance separating its hosts. Unfortunately, a solely numerical metric will not distinguish the two.

Which brings us back to my point that the two Nature papers are not as contradictory as they first appear. The paper from Papua New Guinea compared species from different areas of the same genus. It looked at a different level of resolution than the Dyer et al. paper. As for the implications of the Novotny et al. paper for short-range endemism, the obvious point seems to be that most short-range endemics appear in taxa such as arachnids, myriapods and troglobites - taxa with relatively low dispersal capabilities. In contrast, Novotny et al. looked at insects - winged, and therefore one would expect able to disperse over greater distances more easily, so long as a suitable host plant was present when it got there. In support of this, spiders that disperse by a 'ballooning' stage when young (such as Nephila, the golden orb weaver) tend to be far less diverse with individual species found over much greater areas.

Of course, the number of potential host species in the tropics is still doubtlessly a factor. But this just begs a further question. If insects are so much more diverse because the plants are so much more diverse - then why are the plants more diverse?

PS. I really feel that I should mention that the study by Novotny et al. had a large proportion of the fieldwork conducted by locally trained staff, a number of whom are in the author list below. With the low levels of scientific education available in third world countries, the organisers of this study are to be commended on this front.

REFERENCES

Dyer, L. A., M. S. Singer, J. T. Lill, J. O. Stireman, G. L. Gentry, R. J. Marquis, R. E. Ricklefs, H. F. Greeney, D. L. Wagner, H. C. Morais, I. R. Diniz, T. A. Kursar & P. D. Coley. 2007. Host specificity of Lepidoptera in tropical and temperate forests. Nature 448: 696-699.

Novotny, V., P. Drozd, S. E. Miller, M. Kulfan, M. Janda, Y. Basset & G. D. Weiblen. 2006. Why are there so many species of herbivorous insects in tropical rainforests? Science 313: 1115-1118.

Novotny, V., S. E. Miller, J. Hulcr, R. A. I. Drew, Y. Basset, M. Janda, G. P. Setliff, K. Darrow, A. J. A. Stewart, J. Auga, B. Isua, K. Molem, M. Manumbor, E. Tamtiai, M. Mogia & G. D. Weiblen. 2007. Low beta diversity of herbivorous insects in tropical forests. Nature 448: 692-695.

Because It's Friday....

...and nothing much seems to be working as it should. Here are a couple of photos to while away the time that were taken last year up at Lorna Glen, a station-turned-into-a-reserve in central Western Australia. The creature above is an absolutely massive mantis that we came across - I can't give you a more specific ID, I'm afraid. Hopefully the hand gives you some idea of the scale of the thing - it was at least four inches in length, possibly longer. And if you look really closely, you may be able to make some of the relatively minute ants that were making its life difficult when we found it - they were busily attacking the sensitive joints between leg segments.

Moloch horridus, the spiny devil or moloch, is arguably the strangest-looking of all reptiles, and I can assure you that they look even stranger in the flesh. They have an odd jerky way of moving, the closest thing to it in appearance being old stop-motion model animation. And they are perhaps the most docile animals in all existence - an attempt to pick one up will spark an instant outburst of absolutely nothing. The picture below, I think, gives an idea of how energetic and fractious molochs aren't.


Perhaps the most abundantly obvious group of animals in the area were grasshoppers. One of the common species was a spotted, brachypterous form (Greyacris picta or something similar*) that I thought was a nymph until one day we found this mating pair (the little guy on top is the male).

*I originally IDed them on this post as Monistria pustulifera. A comparison of the excellent photos in Rentz et al. (2003) (a generally excellent book) set me right.

Update: A reader has suggested that the mantis may be a species of Archimantis. He also confirmed my ID of the grasshopper as probably Greyacris, though not necessarily G. picta itself.

REFERENCES

Rentz, D. C. F., R. C. Lewis, Y. N. Su & M. S. Upton. 2003. A Guide to Australian Grasshoppers and Locusts. Natural History Publications (Borneo): Kota Kinabalu.

What is a Daddy-Longlegs?

"Daddy-longlegs" is one of the worst animal names there is. The name is widely used and generally recognised, but causes endless confusion because it is applied to no less than three very different animals. In a brief attempt at disambiguation, these are the animals involved:

First are harvestmen of the order Opiliones (picture from UMMZ). Harvestmen are often confused with spiders, but the body is not divided into a cephalothorax and abdomen, the opisthosoma (the posterior part of the body corresponding to the abdomen) is externally segmented, the chelicerae (mouthparts) are pincers rather than fangs, and harvestmen do not produce silk. The name "daddy-longlegs" as applied to harvestmen usually refers to the group known as "long-legged harvestmen" (Palpatores). There is some uncertainty about whether Palpatores are a monophyletic group, but that's a subject for another time.

Second are spiders of the family Pholcidae (picture is from Iziko Museums of Cape Town - the object the spider is holding is the egg-sac, which is carried by the female until the eggs hatch). Pholcids are true spiders, and so have a divided body, an unsegmented abdomen, fangs, and produce silk. Here in Australia and New Zealand, the 'daddy-longlegs' that are almost ubiquitously found in houses (particularly bathrooms) are pholcids, most often the introduced Pholcus phalangioides. Offhand, there is a common belief that daddy-longlegs (either pholcids or Opiliones) are "the most poisonous spiders in existence, but their fangs are too small to pierce human skin". I have come across this story many times, and have even been assured of it by people who really should know better. This story is absolute bunkum. The University of California, Riverside site has more info.

Finally, the third group accused of being 'daddy-longlegs' are crane flies of the family Tipulidae (picture from Wikipedia). Crane flies look a bit like giant mosquitoes, but they are not blood-suckers. They are a large family - the adults are nectarivores or do not feed, while the larvae, commonly called leatherjackets, feed on vegetation. Crane flies are easily distinguished from the other 'daddy-longlegs' - the wings are a bit of a give-away.

(Possibly) The World's Smallest Tetrapods

The subject of today's post are proturans. Proturans are rather unique little hexapods (though not, by the currently used definition, insects) that are apparently widespread despite being rarely seen (Imadaté, 1991). I have to confess that I've never seen one yet in my time in entomology - I was reminded of them because one of my co-workers briefly thought he might have found one (but alas, not to be - it was probably some form of beetle larva). The title for the post derives from the fact that, despite being hexapods, proturans are functionally quadrapedal. They lack antennae, and instead the first pair of legs is held up and in front of the body as sensory organs. Christopher Tipping has a page with some neat pictures - in particular, check out the 1907 drawing at the top of the page like something on the cover of an Edgar Rice Burroughs book.

Protura show a number of other unique features as well. They are the only insects to increase the number of abdominal segments over their life. And perhaps most notable of all, their spermatozoa are completely unlike any other hexapod (Baccetti et al., 1973). The proturan spermatozoon is non-motile, varying from a complicated twisted helical structure (Acerentulus traegardhi and Acerentomon majus) to a simple mammalian-blood-cell-like torus (Eosentemon transitorium). In those species that retain an axoneme (the flagellar 'skeleton') it shows an abnormal arrangement of microtubules. In the vast majority of eukaryotes, the axoneme has a '9 + 2' arrangement - nine pairs of microtubules around the outside and two single microtubules in the centre (this is also the same arrangement as in spirochaetes, a clade of spiral bacteria, which has lead to rather controversial suggestions that the eukaryote flagellum may be derived from symbiotic spirochaetes - a suggestion I happen to be rather skeptical of). In contrast, proturan axonemes show a whole range of arrangements - 12 + 0, 13 + 0, 14 + 0 or even 9 + 9 + 2. Such unique features have lead to suggestions that proturans may not even be related to insects (there was an article in Simonetta & Conway Morris, 1991, that I recall, but i haven't been able to find the specific reference), but as they are undoubtedly unique derived features of proturans they are completely uniformative as to outside relationships.

In terms of actual phylogenetic relationships, proturans are entognathous (that is, the mouthparts are recessed into a capsule under the head). Most authors have united them with the Collembola (springtails) in a clade called Ellipura, but most of the supposed characters of this clade reflect character losses, which are generally regarded as less trustworthy due to the higher chance of homoplasy. A couple of recent papers did not support the Ellipura grouping (Giribet et al., 2004; Luan et al., 2005), instead placing Protura with Diplura, but the former paper also found an unexpected polyphyletic arrangement of hexapods relative to crustaceans which requires further investigation.

REFERENCES

Baccetti, B., R. Dallai & B. Fratello. 1973. The spermatozoon of Arthropoda. XXII. The '12+0', '14+0' or aflagellate sperm of Protura. J. Cell Sci. 13: 321-335.

Giribet, G., G. D. Edgecombe, J. M. Carpenter, C. A. D’Haese & W. C. Wheeler. 2004. Is Ellipura monophyletic? A combined analysis of basal hexapod relationships with emphasis on the origin of insects. Organisms, Diversity and Evolution 4: 319-340.

Imadaté, G. 1991. Protura. In The Insects of Australia (CSIRO) pp. 265-268. Melbourne University Press.

Luan, Y.-X., J. M. Mallatt, R. D. Xie, Y.-M. Yang & W.-Y. Yin. 2005. The phylogenetic positions of three basal-hexapod groups (Protura, Diplura, and Collembola) based on ribosomal RNA gene sequences. Molecular Biology and Evolution 22: 1579-1592.