Barf out! What's in that pellet..?

Nope, not the feeling that you've eaten too much cake and turkey... while out feeding the birds this morning, I couldn't help but notice what I assumed were pellets from berry-feeding birds (all birds make pellets of undigested stuff, not just owls). OK, so there were bits of seed and berry skin, but also some maggots.... mmm, nice. These were clearly dead, so I had to wonder whether they were egested by the birds (i.e. having been swallowed along with berries) rather than being parasitic. So, one of the little beasts was brought indoors to scrutinse under the microscope.

Fly larva

It was about 8mm long and 1mm wide, whitish and more-or-less cylindrical with a tapering head which included dark mouthparts (fly larvae often have dark chitinous mouthparts).There were no legs, although the underside did have rough pads likely to be used to aid locomotion.

Magnified head showing dark mouthparts.

Closer still to see where the mouthparts protrude.

One of the rough locomotory pads, near the rear end.

Now, the next step is to see if the larva is identifiable. The overall form suggested 'Muscidae' (the houseflies) to me, but to be sure requires a closer look still. So, to the dissecting needles to tease out the mouthparts...

Close-up of the mouthparts while still in the head segment.

Overall shape of mouthparts - note the prongs and notches.

Again, an overall view with attached muscle fibres etc.

Handily I have a copy of Smith (1989) which covers the immature stages of British flies though not always to species level. The prongs of the pharyngeal sclerite (ps), the long, more-or-less parallel structures pointing to the right in the two photos directly above, are about the same length and there are four; these are paired and so only two are seen side-on. In front of (i.e. to the left) of these is the small hypopharyngeal sclerite (hs) and in front of this, a larger structure made of several small sclerites analagous to jaws. In the same two photos you can see the notch between ps and hs, and in the middle photo what appears as a hole is a gap between the parts of the 'jaws'.

So, what is it? Well, the mouthparts and overall body form strongly suggest that it is in the family Muscidae, though I'm can't be sure beyond that as the spiracles were difficult to see. It looks closest to Phaonia sp. though most muscid larvae are carnivorous (e.g. hunting other larvae in damp places or organic matter) and found in various substrates. Therefore, it could easily have been picked up by a foraging bird and then deposited dead but undigested with fruit remains. Any thoughts, including revised ID (e.g. could it be Dolichopodidae instead?) most welcome...

Reference


Smith, K.G.V. (1989). An Introduction to the Immature Stages of British Flies. Diptera Larvae, with Notes on Eggs, Puparia and Pupae. Handbooks for the Identification of British Insects 10(14).

Have a cool Yule...

Hi all,

Time for a few festive days off from ecological and related musings, so season's greetings, and here are some of the favourite pics my camera has kindly provided for me recently :)

Reindeer in Britain: ecology, conservation and welfare outside their native range

Known as caribou in North America, reindeer (Rangifer tarandus) were once widespread in Europe reaching as far south as Spain, but are now mainly found in Norway and parts of Russia, in some cases being found wild alongside domesticated herds. Whilst their bones occur frequently in prehistoric middens, the last reliable record in Britain was approximately 8,300 years ago after which they disappeared (later records are uncertain), probably due to climate change, although hunting pressure may have also been a factor. However, 29 reindeer were reintroduced to Scotland by Swedish Laplander Mikel Utsi in the 1950s. Despite some climate-related difficulties such as troublesome insects, the herd generally thrived, although mortality rates are raised due to dog attacks and eating discarded litter. The herd is now managed at 130-150 animals across two areas - the Cairngorms and the Cromdale Hills – and are the only genuinely wild (if managed and visited) reindeer in Britain. There are other more-or-less free-ranging herds such as at the Trevarno Estate near Helston in Cornwall. These animals were introduced as a Christmas attraction in 2008 and have acclimatised to the warmer-than-Arctic weather, even producing the first calf in England for probably thousands of years in spring 2010.

Reindeer on short montane grassland.

The lack of fecundity is unsurprising given the challenge of the English climate (OK, it’s cold at the moment, but...) especially in the south-west. Reindeer are cold-adapted and fond of their Arctic diet of mushrooms, lichens and other vegetation with their associated minerals. Reindeer’s cold-adaptations include short legs, ears and tail, a hairy muzzle, broad flat hooves for walking on snow (winter) and boggy ground (summer), dense winter coats and particularly rich milk (more than 20% fat while human milk is 3.5% fat) to help the young survive and grow in cold conditions. They are also poorly adapted to the diseases and parasites found in the warmer areas of Britain, with reports of animals dying prematurely having been imported for festive grottos and parades (especially following relaxation of quarantine rules), and subsequently being exposed to diseases from British livestock, along with issues of poor diet and welfare, and the stress of transportation from large semi-wild herds.

Reindeer on grasslands below mountains.

Research by Hughes et al. (2008) on Canadian animals suggests that even in the Arctic, parasites may impact populations by worsening the effects of forage availability (which is seasonal and limited) on individuals’ condition, fecundity and survival. The study showed that, in females over 2 years old, by the end of winter there was a significant decrease in body weight with increased nematode burden, and a decrease in back fat depth with increased warble-fly (Hypoderma tarandi) abundance (which was also associated with reduced chance of being pregnant). Although not directly relevant to the British population, it is possible that muskox (Ovibos moschatus) share some parasite species with reindeer, leading to elevated burdens in the co-host. Thus, parasites may have contributed to a previous shift in winter range by reindeer herds, suggesting in effect a type of competition between the two species. If a similar effect were seen in Britain, reindeer would be unable to shift away from the effects of disease and parasites as most are in captivity (often with relatively inexperienced owners/handlers), while the wild Scottish herd is constrained within a limited area. Thus welfare and animal husbandry standards need to be high (at present, reindeer owners do not have to report unusual deaths to the Veterinary Laboratories Agency, so rigorous research and scrutiny is difficult) and it is important to understand the ecology of such an Arctic-adapted species when introduced into a warming temperate environment.

Lastly, predation; there may be none of the large 'typical' predators such as wolves in Britain (yet), but there is video evidence from Finland of golden eagles (Aquila chrysaetos) hunting reindeer calves - I've not heard of this happening in Britain, but with golden eagle numbers having increased in Scotland, I would be very interested to hear if this behaviour has been witnessed...

For general background information on reindeer, click here.

Bye for now - and season's greetings! Got any lichen...?

Reference

Hughes, J., Albon, S., Irvine, R., & Woodin, S. (2008). Is there a cost of parasites to caribou? Parasitology, 136 (02), 253-265 DOI: 10.1017/S0031182008005246

Picture credit

Thanks to ‘Animal Photos’ for making these images available via the Version 3.0 Attribution-ShareAlike Creative Commons License.

What’s in the box? Diary of a beetle recording scheme

If you are in any way involved in biological recording as a volunteer, you’ll know the process – you see or collect a specimen and if you can identify it (or find someone you know who can), you write up the record in whichever format is appropriate, then send it off to the scheme organiser or records centre. In the UK, this is of huge importance – estimates vary, but the majority of biological records come from volunteers, from relative beginners to highly-experienced amateurs and professionals doing a bit extra in their spare time. If I remember rightly, around 90% of botanical records for the British ‘plant atlas’ were from volunteers with around 70% of records being collected voluntary for all species groups combined. As atlas publications need records, and conservation objectives are often based on biological data, it is clear how vital volunteer recorders are in Britain – some other countries such as France and Germany differ, with recording being undertaken mainly by paid workers, but focusing more on key policy-related species.

However, what happens when you get a specimen, lets say an invertebrate, that you can’t identify? You might know what family it’s in, or even genus, but the species eludes you. You look up the relevant recording scheme and get in touch with the scheme organiser – they may be able to offer advice, and might even be able to identify the beastie from a photo. However, if not (let’s say it needs dissection and more specialist references than you have access to), you might package it up and post it off to them. Well, in my ‘spare time’ I am one such such organiser, so I thought I’d share my view of this end of the process.

Not having had any recent enquiries, when a mystery Jiffy-bag landed on my doormat the other day, I was intrigued to find within a small plastic pot containing a small carded beetle and collection labels, a letter explaining its provenance and attempts to identify it and an address label and stamps to facilitate its return. Apart from not asking first (tut tut, a quick email to check availability is appreciated), this is exactly what I’m after – clear background info, and return postage for specimens.

A couple of days later I had time to look at it – described as having been swept from dune grassland in Cumbria during September, and identified by the sender as probably the genus Longitarsus (a flea beetle within the family Chrysomelidae). My first thought (apart from ‘yes it is Longitarsus’) was how neatly glue-mounted it was – at 2mm or so long, pinning would have been a challenge...

L. suturellus dorsal view - still mounted on its card.

The sender had got stuck at species level, getting contradictory results from use of Joy’s Practical Handbook (one of the beetle books, though many sections are now out of date) – particularly due to results indicating species not found in Cumbria. Now, I have written a key to the Chrysomelidae (though it’s not yet complete and is about to undergo its first major revision having been tested this summer). Working through this, I kept coming to the same result, L. lycopi. Hmmm... that’s not right – not only is it hardly ever found in Cumbria (that doesn’t mean it’s wrong, but warrants closer checking), but despite the key, it didn’t look quite right (shape, colour etc). I had a feeling that the problem was with my key rather than the specimen (especially as I knew which species it looked like, but this was a good excuse to test the key further). So, going back to some other references, I realised which key couplet was the problem – the couplet was correct in itself, but needed further clarification regarding the sometimes fiddly process of looking at the lines and grooves on a tiny beetle’s ‘face’.

L. suturellus - the head in close-up.

A tweak to the wording and the specimen consistently keyed out elsewhere – to L. suturellus. This was much more promising (known from Cumbria), but as the genus is notoriously difficult to key to species using external features alone, the next step was dissection. It was a male, and teasing off the end of the abdomen using pins, the aedeagus could be extracted – it is distinctive in this species (somewhat like an ‘hourglass’ constriction with sturdy edges) and so the identification as L. suturellus is confirmed and can be added to the scheme database. The specimen didn’t survive the dissection, but I did mount the aedeagus on a slide and sent that back to the collector who I hope will find it useful for reference.

Aedeagus of L. suturellus

All fairly straightforward, and maybe an hour or so of effort, but it does highlight some important aspects of recording schemes such as this. Mostly, these are due to the fact that they are run by volunteers. Some organisers may work in closely related areas (e.g. as museum entomologists), but others do not. This isn’t necessarily a problem, but does mean that some aspects may be more difficult. For example, a wide range of sometimes obscure, sometimes expensive books and journal papers are likely to be required. Without ready access to an academic library or endless cash, this means reliance on interlibrary loans and the collections of record centres and museums. Now, I am lucky in that I am quite near Winchester where Hampshire’s excellent biological collection is housed. By appointment, I can use this collection (e.g. to check against known specimens), but (and this can be a large ‘but’), this has to be during ‘office hours’ i.e. when I tend to be at work... Fortunately my working life is quite flexible, but museum visits are still very limited, as is space and equipment for maintaining my own collection. Similarly, I am an inveterate bookworm, and have put a lot of time (and cash) into acquiring specialist papers and books, but still have a wish list of texts I haven’t been able to afford or obtain via inter-library loan (yet). Maybe I need to ‘monetise’ my blog!

Of course, recording schemes develop as does my involvement – I will continue to accumulate key texts, and the chrysomelid scheme should have a new website from spring 2011, hopefully with online recording. I also plan to develop a network of identifiers – at present, the scheme is still small as it was dormant when I took it over, but it will grow and with it the workload and the number of mystery Jiffy-bags. Apart from the nearly-grumble about museum access and book-money, I find it most satisfying – my entomological skills grow, and I know that the scheme will provide invaluable data for conservation and research, as well as (I hope) generating wider interest in the group as well as entomology and biological recording more broadly. For more, have a look at my static page on the shiny, shiny Chrysomelidae, and I hope the boxes keep coming...

NBN distribution map of L. suturellus - widespread!

Coastal invertebrates and climate change: evidence for risks & opportunities

Whichever group of terrestrial invertebrates grabs your attention in Britain, it’s hard not to notice, and read about, changes in species‘ distribution with warming temperatures. Mainstream books (e.g. Smallshire & Walsh 2004) give suggestions for future vagrants and colonists to look out for, while even a cursory look at the topic gives any number of anecdotal references to invertebrates moving further north into or within Britain, including coastal species spreading inland. However, what systematic evidence is there for such range expansions?

With funding limited, many British species are recorded somewhat fragmentarily and although new locations may be noted, it can be difficult to find rigorous monitoring of northward or inland spreads. However, an excellent example is the work undertaken by Musolin (2010), looking at expansion in Japan of the southern green stink bug Nezara viridula (a species which, in 2003, also colonised Britain where it is known as the southern green shieldbug or the green vegetable bug.) Along with Tougou et al. (2009), this showed a clear northward range expansion with warming temperatures, especially along the warmer coasts and via urban areas which form ‘heat islands’. The species is native to Japan which is at the northern edge of its Asian range, but as in Britain, its spread does depend on its ability to overwinter and possibly the need to adapt its diapause period. In Britain, although there have been specimens imported with vegetables or pot-plants prior to 2003, it is only recently that the species has been able to overwinter, and although its status is not entirely clear, it has already spread from its initial locations in north London as well as appearing on the south coast.

NBN distribution map of Nezara viridula (as of 16/12/2010)

Looking at another Hemipteran species reported to be spreading in Britain, the striking red and black rhopalid Corizus hyoscyami, a similar pattern is seen. Generally considered to be a species of sandy coasts in southern Britain, it has recently spread further north (especially the west coast) and has been seen much more often at inland locations, including on mint in my partly-sandy back garden this summer, about 10km inland. I am unaware of any systematic work on this species, but a quick look at the data held by the National Biodiversity Network (NBN) for this species shows that the northernmost records (grid square SH, covering NW Wales) all occur since 1993 with one in each of 1993, 1995, 1997 and 1998, two in 2000, one in 2001 and 3 in 2005. Although this doesn’t form a pattern in itself, it does suggest a northward movement as there are numerous earlier records from previous decades (and indeed centuries), but none so far north, with most along the south coast. Although the NBN database isn’t complete (my record isn’t there yet, but it will be...), the map does show a few inland records including what appears to be spread upstream along the Severn valley.

NBN distribution map of Corizus hyoscyami (as of 16/12/2010)

C. hyoscyami on mint in my garden, summer 2010.

This clearly isn’t rigorous, but does suggest that, like some other species, C. hyoscyami may be benefitting from warming temperatures allowing it to spread both inland and northward. However, this is of course only one aspect of the story: not only does it imply that northern and/or upland specialists may be squeezed with nowhere to go, but also begs the question about what happens in the longer term? Well, for soft cliff habitats, this has been looked at in broad terms by Whitehouse (2007). Here, the conclusion is that, given the expected rise in sea level, changes to precipitation patterns and increased storm frequency and storm ferocity, most impacts on soft cliff invertebrate assemblages will be negative. These effects will increase erosion rates and so may alter the morphology of many important sites, including through damage associated with destabilisation of slopes - changes in precipitation patterns put assemblages associated with hydrological features such as seepages at particular risk. Some warmth-loving species may be able to spread into other habitats, along with colonisation by species from continental Europe, but the responses of individual invertebrate species to climate change are largely unknown and understudied. However, all likely scenarios seem to suggest that although there will be some winners for whom climate change is a genuine opportunity, this may only be in the short- to medium-term, and that most such assemblages, without appropriate conservation measures (e.g. ensuring suitable habitat areas remain even if not in exactly the same location), are at risk from negative impacts. Saying that, I strongly suspect that some species will surprise us with their adaptability, though I would prefer to see carbon emissions falling so as to minimise such impacts and the subsequent need to ‘hope for the best’...

References

Musolin, D.L. (2010). Range expansion of the southern green stink bug Nezara viridula (Heteroptera: Pentatomidae)
in response to the rapid climate change in Japan. Het News, 15, 4-6

Smallshire, D. & Swash, A. (2004). Britain’s Dragonflies. WILDGuides, Old Basing.

Tougou, D., Musolin, D.L., & Fujisaki, K. (2009). Some like it hot! Rapid climate
change promotes shifts in distribution ranges of Nezara viridula
and N. antennata in Japan. Entomologia Experimentalis et Applicata, 130 (3), 249-258 : 10.1111/j.1570-7458.2008.00818.x

Whitehouse, A.T. (2007). Managing Coastal Soft Cliffs for Invertebrates: Summary Report. Buglife - The Invertebrate Conservation Trust, Peterborough.

Awww, ain't it scute... an Isle of Wight crocodile?

As well as yesterday's iridescent limpet, some other items of interest turned up during my visit to the Isle of Wight. Not least of these, found by my wife rather than me, was the series of fossils below, arranged in what appears to be a couple of rows along a large boulder fallen from the cliff...

Overview of boulderful of mystery fossils; each lump several cm across.

The initial cry of 'I've found a dinosaur' was followed by thoughts of 'yeah, right' and then 'er, well, actually...' and so a more careful look was needed. Now, I'm no palaeontologist, but dark pitted lumps in a pale matrix shout 'fossil bone' at me. Or maybe coral... The structure was pitted and compared favourably with a chunk of brontosaurus I've got on the shelf (the small holes and channels were visible, but I wasn't able to get a photo where they showed up clearly), but most interesting were the smaller (a few cm) volcano-like structures protruding from the boulder in a few places among the lumps of maybe-bone.

Above and below, two of the interesting 'volcano' structures (both about 5 x 2.5cm)

 

A bit of research online and even in books started nudging my thoughts away from coral and towards scutes (rectangular-ish armoured skin plates) from a crocodilian of some sort. Many images from these sources appear pitted (not unlike a crumpet in texture) but others are similar to the two photos above. Also, a well-known palaeontologist-blogger suggested the same, so I'm feeling cautiously vindicated at present - and of course, there could be coral, and other things, in the boulder too. However, thoughts on this are most welcome, and there will be an update if anything changes. Until then, my wife's feeling very pleased with herself...

Iridescence in the common limpet (Patella vulgata)

Limpets are familiar seashore animals and school biology (well, mine anyway) tells us about the conical shells that allow them to remain attached and store water in the challengingly energetic and sometimes inconveniently dry conditions of the intertidal zone. However, looking at an empty limpet shell on the Isle of Wight a couple of days ago, I couldn’t help but notice the iridescent colours inside its peak. The white colour is, if I remember rightly, one why of identifying this limpet species, but the iridesence is something generally associated with other molluscs such as ormers, abalones, top shells and of course oysters and their pearls.

Inside an empty limpet shell.

Now, I know that I’ve seen iridescence in all sorts of mollusc species, and am aware that the colours are due to the effect of small-scale structures of a size similar to the wavelengths of light and the resulting interference patterns. What piqued my curiosity was what these structures actually are and why they exist – given that the colours are often hidden away inside shells, it seems that they must be an aesthetically pleasing by-product of something with a function other than the decorative; is it simply the crud-capture associated with pearl formation?

Close-up of limpet iridescence

Nacre or ‘mother-of-pearl’ is a composite material (organic and inorganic) made of thin layers of hexagonal platelets of aragonite (a type of calcium carbonate) separated by sheets of elastic biopolymers such as chitin and silk-like materials. This structure is strong and crack-resistant (more precisely it resists crack propagation) and smooths the inside of the shell. It also helps defend the animal against parasites by encysting them in layers of nacre. So, it is both structural and a capturer of crud, which incidentally  happens to be iridescent due to the size of aragonite platelets. Limpets may not be the most well-known iridescent mollusc, but they deserve their place here (there are other types of layering and shine forms in the molluscs as well); for an electron-microscope close-up, have a look at images from the University of Tokyo’s Kogure Lab here (scroll down to number 6 for limpets).

After the dung-fly: parasite effects on human behaviour

Following my recent post about behavioural modification of insects by Fungi such as Entomophthora, I was sufficiently intrigued to digress from my usual ecological and entomological subject matter and look at work on related processes in humans. Rather than a fungus, the organism I am particularly interested in is the widespread parasitic protozoan Toxoplasma gondii.

Spread to humans (and many, many other species) by various mechanisms including handling and consumption of raw meat, transplacentally, faecal contamination and via members of the Felidae, this organism causes toxoplamosis, the main symptoms of which are widely described (e.g. here). However, less well understood is the possible link between T. gondii infection and changes in human behaviour. Some studies (e.g. Henriquez et al. 2009) have indicated a link (causative or contributory) between infection and several psychiatric disorders such as depression and schizophrenia.

Other work has shown behavioural effects on rodents, and subsequently on humans (Flegr 2007). Along with some quite complex changes in personality traits, the effects of which appear to differ between men and women, some clear practical impacts were seen such as reduced reaction time (i.e. reduced psychomotor function). Now, in insects, behavioural changes by parasites have clearly evolved to improve the reproductive success of the parasite (such as the posture adopted by Entomophthora-infected flies which aids spore dispersal), but what about in vertebrates? Flegr (2007) helps here too. Reduced reaction time in rodents coupled with a felid host makes intuitive sense – slower mice and rats are more likely to be eaten by cats. In humans, the link is less obvious until you consider the ‘point of view’ of the parasite i.e. that it doesn’t know it is in a dead-end host – one that is highly unlikely to be eaten by a cat. So, the behavioural change still takes place, and impacts may be felt, or at least detected by targeted research. This logic holds true for another known effect on rodents – risk-taking behaviour which manifests as reduced fear of cats (and even active seeking of locations with cat urine) – which some studies such as Henriquez et al. (2009) have noted in humans (as increased rule-breaking rather than urine-seeking...). Again, this makes clear sense – unwary rats get eaten by cats.

The precise mechanism causing such changes is still not fully understood, but recent research (Webster & McConkey 2010) at the University of Leeds has found that T. gondii produces an enzyme with tyrosine hydroxylase and phenylalanine hydroxylase activity which may alter dopamine production and so affect mood, sociability, attention, motivation and sleep patterns. Linking back to the psychiatric conditions noted above, schizophrenia has long been linked to dopamine dysregulation. Ongoing research seeks to elucidate the mechanism of T. gondii effects at the molecular level. Personally, I find this fascinating - complex human behaviours being modified by a protozoan we often don't know is there (even if maybe a third of us have it), but back to the ecology...

References

Flegr, J. (2007). Effects of Toxoplasma on human behavior. Schizophrenia Bulletin 33(3): 757-760.

Henriquez, S.A., Brett, R., Alexander, J., Pratt, J., & Roberts, C.W. (2009). Neuropsychiatric disease and Toxoplasma gondii infection. Neuroimmunomodulation, 16 (2), 122-133 PMID: 19212132

Webster, J.P., & McConkey, G.A. (2010). Toxoplasma gondii-altered host behaviour: clues as to mechanism of action. Folia parasitologica, 57 (2), 95-104 PMID: 20608471

As the snow clears...

...well, it's clearing in the south of England at least, and as it does so, I can't help but muse on the rapid and ephemeral change I've seen over the last week or two in the bird life visible from my office window. Now, I've not written much about 'backyard wildlife' so far, though not for any other reason than other topics keep grabbing my attention. However, after last winter's well-documented appearance of the thrush species redwing (Turdus iliacus) and fieldfare (Turdus pilaris) in gardens around Britain during frozen conditions, I was curious to see what would happen this time.

Prior to the wintry conditions, the usual birds were present e.g. house sparrow (Passer domesticus), goldfinch (Carduelis carduelis), blue tit (Parus caeruleus), great tit (Parus major), wood pigeon (Columba palumbus), collared dove (Streptopelia decaocto), jackdaw (Corvus monedula), blackbird (Turdus merula) and starling (Sturnus vulgaris). So, a typical mix of birds using feeders and other food sources in the garden, including seeds dropped from the feeders. However, within a day or so of snow and ice, the species mix had changed. The above were all still present, but starling numbers had risen from 6-10 to around 20 and robin (Erithacus rubecula) and coal tit (Parus ater) were using the garden regularly rather than occasionally. Also, species not seen during warmer weather appeared; one each of pied wagtail (Motacilla alba) and wren (Troglodytes troglodytes), brief swoops to take food by two black-headed gulls (Larus ridibundus), and most unusually a brief visit by a grey heron (Ardea cinerea) - possibly seeking food away from the usual, currently frozen, sources (although the local river is not frozen)?

None of these are at all uncommon, but as well as highlighting the importance of gardens as food sources, they do suggest that such observations can shed light on short-term changes in the behaviour and distribution of familiar species. If there's another 'big freeze' (otherwise known as 'winter'), watch this space for more...

Tree, snow and colour-tweaking.

Local woodland looking darn seasonal.

Chilly tussocks! It's the rare Snowy Land Urchin Echinus nivalis.

Rice Weevil – how far does its polyphagy go?

The adaptable and wide-ranging feeding behaviour of the Rice Weevil Sitophilus oryzae is well documented e.g. by Trivedi et al. (2010) who have analysed a range of metabolites in weevils fed on different diets. Along with its ability to fly to new food sources, this adaptability has led to its status as a ‘post-harvest’ pest of stored produce. Although now cosmopolitan in distribution, confusion between this species and the similar S. zeamais (and likely mixing in collections) means that its exact distribution in Britain is unclear (Morris 2002).

However, on 3^rd Dec 2010, whilst buying bird-food, I did find some Sitophilus weevils under the rim of a tub of dried mealworms being sold in a hardware store. There were four live individuals which could not be collected, but two were dead or moribund and these came home along with the mealworms (which are currently being feasted on by starlings on my bird-table.) The species’ separation is relatively straightforward by dissection as the median lobe of S. oryzae is dorsally smooth without longitudinal sulcae, unlike that of S. zeamais which has two sulci. The specimens turned out to be S. oryzae.

Adult S. oryzae from the hardware store (approx. 2.5mm long)

Underside showing antennal insertions beneath swollen rostral base.

Dorsal view showing punctures, especially of the pronotum.

Although these will form a useful record of the species, I was interested to know how broad their diet is. Adults and larvae feed on whole grains, and as well as rice, can feed on a range of other cereal crops,  dried beans, cashew nuts, wild bird seed, leguminous pods (Pemberton & de Rodriguez 1981), plus cereal products such as macaroni. Females chew a cavity into a seed, laying a single egg and sealing it in using a secretion from her ovipositor. The larva develops within the seed, hollowing it out while feeding. The larvae and pupae complete their development inside a seed kernel or man-made equivalent (such as macaroni with its handy ready-made hollow space within a wheat ‘shell’) and have been known to develop in hard-caked flour. 

So, given that S. oryzae has expanded its range of foods to include not only other cereals, but also legumes and nuts, could it adapt further to include animal material? Well, it is unclear whether it could feed on animal matter to some extent, but previous research (Chippendale 1972) suggests that this is unlikely to form more than a passing nibble. This is because it appears that the branched-chain amylopectins of cereal starches acts as both a feeding stimulant and an essential nutrient – without this, the weevil simply doesn’t feed and starvation is seen. So, although its culinary tastes are wide-ranging it is not omnivorous, and it is likely that the specimens I found were incidental on the mealworm tub having arrived along with more suitable grain and seed-based bird food.

References

Chippendale, G.M. (1972). Dietary carbohydrates: Rôle in survival of the adult rice weevil, Sitophilus oryzae. Journal of Insect Physiology 18(5): 949-957.

Morris, M.G. (2002). RES Handbook Vol.5 Part 17b: True Weevils Part 1. Coleoptera: Curculionidae (Subfamilies Raymondionyminae to Smicronychinae). RES, London.

Pemberton, G.W. & de Rodriguez, A. (1981). The occurrence of a strain of Sitophilus oryzae (L.) (Coleoptera: Curculionidae) breeding in Portuguese kibbled carobs. Journal of Stored Products Research 17(1): 37-38.

Trivedi, A., Kaushik, P., & Pandey, A. (2010). Identification and metabolite profiling of Sitophilus oryzae L. by 1D and 2D NMR spectroscopy. Bulletin of entomological research, 100 (3), 287-296 PMID: 19814847