Little larvae that love leaves

As you may know, I specialise in leaf beetles (Chrysomelidae) and quite often get sent specimens to identify as I run the national recording scheme for this family. These are usually adults, but now and again juvenile stages which are more difficult, but also useful reference material, especially as I (eventually) intend to write a guide to their identification. Some months ago I was sent some larvae preserved in alcohol to see if I could confirm whether they were Chrysolina marginata. It took me a while to find the time for this (it's been a busy year), but here's the process.

Tube of preserved larvae.

Contents of the tube. The larvae are of different stages (instars) and the largest ones are around 7-8mm long. The anal proleg is visible (especially in the specimen top right) and this is a feature of Chrysolina.

Sensory structures on the head. There are no compound eyes, but in Chrysolina there are six ocelli (simple eyes) on each side of the head as indicated by green arrows, four in a rough square and two the other side of the antenna which is circled in blue. The segmentation of the small antenna is clearly visible, including the small segments/structures at its tip.

Side view of one of the larger larvae. The blue lines show the joints between segments. The green lines show sclerites (hardened patches) arranged in irregular rows.

The end of one of the legs, showing the tarsal claw. The inset shows that the outline (solid) has no protrusion at the base. This is a feature of C. marginata with some other species having a protrusion (dotted line).

Close-up of the body surface. Sclerites are shown in green circles. The pale blue arrows show intermediate secondary bristles with small dark patches at the base of each. Between these there are tiny dark dots of microsculpturation as shown within the dark blue outlines. This mixture of features is seen in C. marginata.

So, the combination of features, along with the keys in Marshall (1979) and Zaitsev & Medvedev (2009) confirms that these larvae are C. marginata - easier than larval identification often is, and provides information that is due to be used in a report later this year.

References

Marshall, J.E. (1979). The larvae of the British species of Chrysolina (Chrysomelidae). Systematic Entomology 4: 409-417.
Zaitsev, Y. M. & Medvedev, L.N. (2009). Larvae of Leaf-beetles of Russia. KMK Scientific Press, Moscow. [In Russian]

This is why I geek those beetles

If you are a regular here, you'll know I spend a lot of time peering closely at small invertebrates in order to identify them, like here. For those interested in taxonomy and morphology (like me), that can be an end in itself - I find small creatures fascinating and I like to know what they are. I geek them, and do so proudly - plus I'm a professional entomologist/ecologist so there's the academic-kudos and getting-paid aspects. However, there is more to it than that.

I have been asked more than once why we need to identify species - and it's a fair question; after all, the beetles don't care whether we can name them, and individual ones would probably prefer not to be fatally sampled for the greater good. However, without identification (which often requires a dead specimen), there can be no survey, monitoring or collection of distribution data; and without these, we don't know what needs conservation effort. In an ideal world, their habitats would be fine, biodiversity would not be threatened, and conservation (if needed given the previous points!) would have limitless funding. Sadly these things are very very much not the case. So, samples are taken, species are identified (along with date, location etc) and data sent to recording schemes/centres, or now added to online systems such as iRecord to be validated by hard-working volunteers such as myself...

Once the data has made its way to the recording scheme database, it can be downloaded, interrogated - in short, used. This could be for any number of purposes - planning, research, amatuer interest, and so on. However, during the winter of 2013/14 I was lucky enough to be contracted to use this data to write a status review of the Chrysomelidae (leaf beetles), the group I specialise in. This meant looking at the change in distribution of all the British species and allocating them to categories such as 'Least Concern', 'Endangered' and 'Vulnerable'. Thus, scarce and threatened species could be identified and highlighted with extra information focusing on these, such as summaries of habitats, distribution, threats and conservation measures. This is important as it will inform conservation efforts, survey work, policy decisions and other activities. It's also part of a wider project with different specialists covering their groups of choice such as Carabidae (ground beetles) and is a major update to status review work published in the 1990s (e.g. Hyman & Parsons, 1992) some of which is now considerably out of date.

I won't go into any more detail here, but if you want to look at the report, it's called A review of the scarce and threatened beetles of Great Britain: The leaf beetles and their allies and is free to download here along with data covering the key species.

Reference

Hyman, P.S. & Parsons, M.S. (1992). A review of the scarce and threatened Coleoptera of Great Britain 1. JNCC, Peterborough.

March of the green vomit-grubs

As you may know, I am a stakeholder in a nearby community farm, here in the sometimes-sunny south of England. We grow many different crops and one of these is a small patch of asparagus. So, I was interested to see some beetle larvae eating the leaves and stems. Fortunately they don't seem to be affecting the asparagus growth noticeably so they've been left where they are (we don't use pesticides but could remove them by hand if they become a problem). Handily, I specialise in chrysomelids (leaf beetles) and recognised them as larvae from this family: the small shiny head capsule, and the body widening towards the rear then coming to a blunt point is typical. I've been looking at writing a guide to juvenile chrysomelids so in this case, knew they were larvae of the asparagus beetle Crioceris asparagi, and the presence of the distinctively colourful adults confirmed it.

Larvae of Crioceris asparagi along an asparagus stem. Adults in the background.

Late instar larva of C. asparagi eating an asparagus stem. This mature larva is close to pupating and shows a typical chrysomelid larval shape (though some differ greatly especially the tortoise beetles in the subfamily Cassidinae).

Larvae such as this are clearly potential prey for insectivorous predators that like juicy grubs. However, while some chrysomelid larvae hide and protect themselves with shields of their own faeces and shed skins, this species has a different approach. When threatened, it arches backwards, raises its head and regurgitates a droplet of partly digested food onto its attacker. This might not do much to a human but could be noxious to a smaller organism, causing the larva to be avoided or giving it time to drop off the plant to safety.

C. asparagi larva with a regugitated droplet on its head.

C. asparagi larva having used its droplet against my threatening finger.

In contrast, a chrysomelid larva (unidentified) with a shield of faeces and shed skins.

Assuming the larvae survive to pupate and emerge from their soil cocoons as adults, their defence changes greatly as they are colourful, warning potential predators that they are (or in the case of this species, are pretending to be) toxic - something known as 'aposematic mimicry'.

C. asparagi adult.

C. asparagi adults creating the next generation.

So, for now I'll enjoy these interesting beetles - hopefully they won't become too numerous...

Nest of tiny delights

Wow - a month since my last post - there has been no shortage of wildlife to write about, just no 'spare' time to do the writing. However, the paid stuff is quiet for a few days at least, so I thought I'd share some observations of the small and hidden, to be precise what I found lurking within a used-and-the-young-fledged robin's nest.

The robin's nest before dismantling.

You never know what'll be hiding in a nest (whether bird or mammal) - there's always the possibility of some under-recorded parasites, plus the array of small invertebrates that simply use the structure as their own. So, a white tray, various tweezers and pins and some time later, this is what I found, along with quite a few Collembola (springtails) and Psocoptera (barklice) which I didn't collect on this occasion as I knew I would have time to work through the identification.

One of three similar pupae a few mm long, currently in my hatchery.

Another pupa, also a few mm long.

A very young spiderling, highly active and I think one of the wolf spiders (Lycosidae)

A tiny dead wasp, probably one of the Pteromalidae, possibly predated by a spider.

The exuvia (skin) of, well, I'm not sure...

Alive and active, the larva of what is probably a 'carpet beetle' (Dermestidae).

So, not much in the way of definite identifications - with juvenile stages, that tends to be difficult, though if any are successfully raised to adulthood, I will as ever update the post. Also, no parasites, but there was good evidence of a thriving community of small invertebrates potentially living out their whole life cycle in the structure of the nest with larvae, pupae, evidence of emergence, predators and prey.

Beetles love big butts and they cannot lie

Spring means many things - for many species overwintering adults re-emerge and set about the important business of reproduction. One common species that is often seen doing this is the green dock beetle Gastrophysa viridula. It feeds mainly on broad-leaved dock Rumex obtusifolius and related species and in April/May patches of dock can be seen with large numbers of these beetles. Such groups can be highly localised however - one patch of dock can have hundreds of beetles while a nearby patch on the same site seems to have none, possibly due to adults clustering for mate-finding purposes - it is not due to mobility as they can fly. Mating is a competitive activity though as males may try to dislodge rivals, and have foot-pads. These appear white around the sides of the tarsi (feet) to help them grip the female.

Two male G. viridula compete for one female.

Gastrophysa viridula as they are often found - a mating pair.

A dislodged male G. viridula draws its legs in for protection.

The females are particularly distinctive as they have swollen abdomens which extend beyong the elytra (wing cases). There are two or more generations per year (possibly up to six depending on temperature and other conditions) and the oval yellowish eggs can be seen in small clusters. The first new adults emerge in June and others appear through to September. They then overwinter from October to April.

Eggs of G. viridula.

Female G. viridula showing the swollen black abdomen.

The adults chew roundish holes in dock leaves, but the black larvae can skeletonise whole leaves until just a network of veins is left. For this reason, where certain Rumex species are considered invasive, G. viridula has been suggested as a potential biological control, though as ever introducing non-native species needs to be considered very carefully to avoid unwanted impacts on native species.

G. viridula larvae feeding on dock leaf.

Springtime beetles, legs go spring

Having a garden pond means occasionally finding dead things floating. No, not hedgehogs or other larger fauna - the sides are profiled so that mammals can get out - but sometimes incautious invertebrates drown. Naturally, if they look interesting (and haven't been eaten by pond skaters and other small predators), I fish them out for a closer look. When I saw a flea beetle (in the Chrysomelidae, my specialist group - they are in the tribe Alticini within the subfamily Galerucinae) I identified it easily enough as Longitarsus pellucidus, a common species, though it's always worth checking. It lives on bindweeds (Convolvulaceae) which are growing near the pond so presumably jumped into the water by accident when disturbed by a spider, bird, cat, human or other potential threat. However, it did give me an opportunity to look at why flea beetles are so named.

Longitarsus pellucidus - the swollen himd femora can be seen, as well as the elongate tarsus that gives it its generic name.

The hind femur in flea beetles is swollen to accomodate jumping muscles and the 'metafemoral spring' which is visible through the cuticle as a slightly paler comma-shaped structure taking up much of the inside of the femur.

Hind femur and metafemoral spring of L. pellucidus.

The spring is a long-oval chitinous structure coiled much like a loose fist. Muscles squeeze the spring closed and then a 'catch' is released and the stored energy is released, extending the leg so the beetle can jump.Here you can see a ligament extending from the spring to the tibia so the leg is folded when the spring is compressed. This mechanism differs from that in fleas which have a blob of resilin (a natural rubber) which is compressed instead of a spring. Although fleas may be more familiar for their leaping ability, some alticine beetles are actually able to jump comparatively further, and of course some of these beetles are no bigger than a large flea - smaller beetles jump further relative to their size (Schmitt 2004). Also, the spring may be useful for identification and for grouping species taxonomically by looking at similarities and differences in the form of their springs. However, this is not a mainstream technique, largely because of the difficulty of dissecting out the spring and the lack of readily available published material forming a guide to identification this way, although there is useful information in Furth (1988) along with images and drawings from various species.

References

Furth, D.G. (1988). The jumping apparatus of flea beetles (Alticinae): the metafemoral spring. In: Biology of Chrysomelidae, eds. P. Jolivet, E. Petitpierre & T.H. Hsiao, pp. 285-297. Kluwer, Dordrecht.
Schmitt, M. (2004). Jumping flea beetles: structure and performance (Insecta, Chrysomelidae, Alticinae). In: New developments in the Biology of Chrysomelidae, eds. P. Jolivet, J. Santiago-Blay & M. Schmitt, pp. 161-169. SPB, The Hague.

What's in the box? Beetle-related joy (part 2)

Following on from identifying a couple of specimens of Aphthona pallida, I was left with one small dark beetle, another Aphthona. This was a female but also very well dissected, and keyed out quite easily as A. melancholica - a gloomy name for a dark-coloured insect.

Aphthona melancholica - female with genitalia dissected out.

As you can imagine, as the beetle is only about 2.5mm long, the genitalia you can see in the above photo are not large. They tend not to be as useful for identification as those of males (as the differences between species are so slight), but can be helpful and are included in some keys such as Doguet (1994). The structure visible here is the spermatheca - the structure that receives and stores sperm.

Spermatheca of A. melancholica

Reference

Doguet, S. (1994). Faune de France 80 – Coléoptères Chrysomelidae, Volume 2: Alticinae. Federation Francaise des Sociétes de Science Naturelles, Paris. [in French]

What's in the box? Beetle-related joy (part 1)

Sometimes I get sent emails with photos of beetles, sometimes I get little packets of unsorted beetles with a letter asking for identification, but sometimes I get beautifully, neatly mounted and pinned specimens and that makes my entomological heart happy. In this case some specimens of Aphthona flea-beetles (Chrysomelidae: Alticini) needing to be checked at species level.

Neat arrangement of Aphthona specimens

The two on the left are similar (yellowish with a dark stripe) and are what I'm looking at here (the other darker one will appear in a separate post). They are both possible A. pallida which needs checking as the species was only recognised as being British (Sinclair & Hutchins, 2009) a few years ago, so its abundance and distribution is not well understood. This doesn't mean it's only just arrived, but that it hadn't been noticed before and was probably confused with the similar A. nigriceps (Jobe & Marsh, 2012).

Probably Aphthona pallida - a male with the aedeagus dissected out. Beetle approx 2.5mm long, excluding appendages.

The yellow-brown colour with a darker head and partial dark stripe along the suture (where the wing-cases or 'elytra' meet) is typical. Looking more closely at the aedeagus, the end has a small blunt point which is the final feature needed to confirm that this, and the other specimen, are A. pallida - in this case found in Cumbria.

Aedeagus of A. pallida - note the small blunt point top left.

References

Jobe, J.B. & Marsh, R.J. (2012). The status of Aphthona pallida (Bach) (Chrysomelidae) in Yorkshire. The Coleopterist 21(1): 19-20.
Sinclair, M. & Hutchins, D. (2009). Aphthona pallida (Bach, 1856) (Chrysomelidae) is a British species. The Coleopterist 18(3): 155-157.

The beetle is dead, long live the beetle

The decline of the leaf beetle (Chrysomelidae) Chrysomela tremula is well known (e.g. Cox, 2007; Hubble, 2012), even though the causes of its probable extinction in the UK are not understood - possibly the decline of coppicing and/or a side-effect of insecticidal spraying. The last known record was from Warwickshire in 1958, so when its rediscovery was reported relatively recently from purple willow Salix purpurea in Cambridgeshire (Mendel & Hatton, 2012), there was much rejoicing. Then, shortly afterwards, the authors realised that this had been a misidentification and they had actually found C. saliceti, a species never before found in Britain (Mendel & Hatton, 2013). So, C. tremula remains probably extinct but we do have a new species. This doesn't mean C. saliceti is non-native - it is very similar to C. tremula and may simply have been overlooked - after all, their separation was tricky enough to briefly trick some very experienced entomologists until another one noticed and the error was rectified - which is how science works...

Then after a discussion at the recent Coleopterists' Day in Oxford, Howard Mendel was kind enough to post me a couple of specimens of the new species as I had never seen one.

Chrysomela saliceti approx 9.5mm long.

Chrysomela saliceti under different lighting to more clearly show the punctures on the pronotum and elytra.

The trick is to separate the two species - especially in case C. tremula is still hiding somewhere (or re-appears from the Continent). A paper about this is planned, but until then, there are two key features:

• The claw-bearing tarsal segment (two apical teeth on the underside in tremula, absent in saliceti).
• Dissection of males to check the tip of the aedeagus (equivalent of a penis).

Tarsus ('foot') of C. saliceti - the claws are visible but no teeth on the underside.

The aedeagi of the two species for comparison.

References

Cox, M.L. (2007). Atlas of the Seed and Leaf Beetles of Britain and Ireland. Pisces, Newbury.
Hubble, D. (2012). Keys to the Adults of Seed and Leaf Beetles of Britain and Ireland. FSC, Telford.
Mendel, H. & Hatton, J. (2012). Chrysomela tremula Fabricius (Chrysomelidae) rediscovered in Britain. The Coleopterist 21(3): 132-135.
Mendel, H. & Hatton, J. (2013). Correction: Chrysomela saliceti Suffrian (new to Britain) not Chrysomela tremula Fabricius (Chrysomelidae) in the cambridgeshire fens. The Coleopterist 22(1): 19.
Warchałowski, A. (2003). The Leaf-beetles (Chrysomelidae) of Europe and the Mediterranean Area. Natura Optima Dux Foundation, Warsaw.

Jolly writing news

No close-ups of invertebrates today - just a quick post to say a big 'yay' 'cos I've just agreed with Pelagic Publishing that I'm writing a book on Leaf Beetles as part of their Naturalists Handbooks series. Woot! I've got a year to write it, then it's due out mid-to-late 2015... Let the typing commence!

What's in the box? Two of one, one of another (part 2)

Yesterday, the answer was Oulema melanopus - today I'm tackling the other two, much tinier beetles. They both look like the one below and were tentatively identified from dissection as male Aphthona euphorbiae. Why tentatively? Well, they can only be separated from closely related species (not to mention some taxonomic confusion with these which I might write about if it's ever resolved) by looking at the aedeagus - the male genitalia - and in these specimens they don't look quite like the standard images in books or on websites like this which are useful for comparison.

A specimen of Aphthona, possibly A. euphorbiae - it is around 2mm long, not including legs and antennae.

Looking at specimen #1, here's the aedeagus:

Aedeagus of A. euphorbiae.

This one's straightforward - it's fairly stubby and although it doesn't widen towards the end (the top), it has got the small, broad blunt tip on the otherwise more-or-less semicircular end. Definitely A. euphorbiae, so onto specimen #2:

Aedeagus of A. euphorbiae.

This one's similar, but under the microscope looked more elongate although the tip is correct. It's probably A. euphorbiae but with the possibility for confusion with A. atrovirens or A. ?atratula (the '?' indicates uncertainty about it's identity/taxonomy), it can be worth checking even common species as this can sometimes help unravel such difficulties, though in most cases it is simply the usual range of variation between individuals even in diagnostic features such as the aedeagus. Anyhow, time for a side view:

Aedeagus of A. euphorbiae.

The curved (but not too curved) form confirms it is A. euphorbiae - a common species but good practice in investigating features that can be tricky in specimens showing a little variation from the norm.

That's enough beetle-nerding from me. Back soon with... hmmm, haven't decided yet...

What's in the box? Two of one, one of another (part 1)

While at the annual Coleopterists' Day at the Oxford Uni Museum of Natural History last weekend, I was handed a small wooden box with three pinned beetles in it. If you are an entomologist, this will be familiar as specimen-swapping is an important way of seeing varied specimens and passing on tricky beasties to specialists for identification. Not that getting a box of beetles was the real reason I was there - there's a really good entomology library to rummage through plus I gave this talk to my fellow beetle-nerds, now published in a slightly more formal version as Hubble (2013).

Box of beetles - two Aphthona on the left, and a larger Oulema.

So, to the beetles - they'd all been tentatively identified, but were passed to me for confirmation. I started with the larger one, 'a female, probably Oulema melanopus'.

Pinned female Oulema - note the blue-black head and elytra and red pronotum.

The female genitalia had been dissected and preserved in a drop of clear mountant. The important part is the little knot bottom-right where 'sd' = spermathecal duct.

An extract from Cox (1995) comparing the female genitalia of O. melanopus and O. rufocyanea, two very closely related species.

Looking at the images in Cox (1995), and the equivalent in Hubble (2012), it is clear that Figure 6 is close to the specimen here, including the short spermathecal duct and arrangement of other tubules. So, this is O. melanopus - good practice at a sometimes-tricky species group aided by some excellent dissection (not mine!). This may be even more useful given that unpublished and ongoing Swiss work on specimens of O. melanopus has shown that a small number of them turn out to actually be O. duftschmidi. There's no indication that this latter species exists in the UK, but it has a Western Palaearctic distribution so it's not impossible and I'll be keeping an eye out...


References

Cox, M.L. (1995). Identification of the Oulema 'melanopus' species group (Chrysomelidae). The Coleopterist 4(2): 33-36.
Hubble, D. (2012). Keys to the adults of seed and leaf beetles of Britain and Ireland. FSC, Telford.
Hubble, D. (2013). Progress report on the Chrysomelidae recording scheme. The Coleopterist 22(3): 103-109.

The Great Juvenile Chrysomelidae Project

You know I like invertebrates, especially insects, in particular beetles, and that I have an inordinate fondness for the Chrysomelidae (leaf beetles). You may even know that I published an identification key to the adults of British species. However, I have (foolishly?) decided that this isn't enough and am therefore embarking on a project to (eventually) produce some sort of identification guide to juvenile chrysomelids - eggs, larvae and pupae.

Why? Well, for many of the species, the ecology and life histories are poorly understood, and many juvenile stages are undescribed. So, it's first of all, an opportunity to summarise where more research/beetle-hunting is required. If the larva of species X has never been described, then there's an opportunity to try to find it. This allows the biology of the group to be better understood and in turn, conservation measures to be more appropriately designed and applied. The better we know them, the better we can protect them.

This is why the first step is the creation of a spreadsheet covering what is known/published for each species on the British list so that I can see where the genuine gaps in our knowledge lie. I have a draft of this spreadsheet and what I'm after is feedback to see what I've missed - presumably some stages/species are covered in publications, grey literature, theses etc that I've not managed to find, as well as observations that have not been written up in keys or formal descriptions. Some blanks could be filled in with a fair level of confidence e.g. more 'earthen cells' for pupal location, but I've erred on the side of caution and left blanks where there's no published (or directly observed) confirmation I know of. There's also a list of all the references I've found so far.

Interested? want to help?

If you'd like to check the spreadsheet and see if there's anything you could add to it, please get in touch so I can email it to you (if there was a wiki function here, I'd use that, but there isn't...). Then simply send any additions to me citing the cell number in the spreadsheet where it should go (either by email or a comment here).

I hope that all makes sense and look forward to seeing what I've missed - I suspect this is going to be a long project...

A chrysomelid larva, but which one?

The ladybird and the cocoon of doom

About 10 days ago, while cleaning one of my stick-insect cages, I noticed an adult 7-spot ladybird Coccinella 7-punctata with a silky cocoon stuck between its legs. Ladybirds don't make cocoons like that - what could it be? Some small invertebrates can be truly difficult to identify, but this one was, for once, straightforward as it is a common parasite of several ladybird species, Perilitus coccinellae, a wasp in the family Braconidae. But, to be sure I put the cocoon in a hatchery and waited...

Perilitus coccinellae cocoon, approx 6mm long

An adult P. coccinellae (a female - males are unknown) did indeed emerge and provides a good opportunity to look at a common, but often overlooked parasite.

 

Adult P. coccinellae - note the wing venation and the needle-like ovipositor with the abdomen curled under the body

Adult P. coccinellae - a closer look at the ovipositor

Adult P. coccinellae - see how the abdomen is curled under the body

The wasp has an interesting life history (as parasites often do). Although ladybird pupae are sometimes targeted, adults are usually parasitised. The wasp taps the ladybird with her antennae then curls the ovipositor forward and begins to tap and probe for weak points, laying a single egg into the ladybird along with trophic ('nutritional') cells which absorb food from the host so the wasp larva can feed on them once it hatches. It does not feed on the ladybird directly, although the diversion of nutrients to the parasite ipacts on the host's reproductive development and fat storage. After reaching its 4th instar, the larva chews its way out from the underside of the ladybird's abdomen, having immobilised it, possibly by affecting the host's motor neurones. It then forms the cocoon which is attached to the ladybird's legs. The ladybird is alive at this point which means that the wasp is protected by its warning colouration and reflex bleeding defence. The wasp then pupates, emerges as an adult and seeks a new host as soon as its wings are dry. The ladybird usually dies within about a week, either of starvation or fungal disease. Some host ladybirds do regain the use of their limbs although most are greatly weakened and die soon after. In winter the cycle stops for a while as the wasp larva hibernates within a host ladybird.

So, a bad end for the ladybird, but an interesting tale - if you'd like to read it in more detail, try Majerus (1994) which contains plenty more interesting ladybird info.

Reference

Majerus, M.E.N. (1994). Ladybirds. HarperCollins, London. [New Naturalist series]