Bark at the Moon - small invertebrates of timber (Part 1)

OK, it's Halloween and I seriously thought about posting something truly ghoulish, but in the end only came up with a slightly cheesy title... mainly because I spent part of the day identifying some small (2-3mm) specimens that I collected from our firewood store. There were some smaller specimens but I have yet to work through them (they may appear here soon); however, I thought it might be interesting to have a look at some of the invertebrates associated with stored timber, especially as they can be brought to our homes by hiding under bark and in crevices when forewood is brought in from elsewhere. Our firewood is all fairly local, so there is unlikely to be abything exotic, but given their small size, it is possible than some of the organisms found might represent under-recorded taxa.

The first of these is a barklouse which as its name suggests is associated with bark. These were numerous and as far as I can tell all those I collected were female and at least some were gravid (contained eggs).

Side view of the barklouse.

Dorsal view of the head showing features including the yellow patches at the inner rear edges of the eyes.

The 'laciniae', end segments of the maxillae (mouthparts) which have a distinctive shape (a 'pie-crust' edge) and are hardened for curtting and manipulating food.

 

The forewing showing hairs, vein/cell pattern and pale larks on an otherwise brownish wing (the other colours are interference patterns and reflections).

These features combine to provide an identification as Epicaecilius pilipennis. This species was first recorded in Britain in the late 1990s but has since been shown to be widespread (whether or not it is common) with specimens from Scotland to the south coast and various locations in between. It is in the family Caeciliusidae within which it is unusual in being associated with tree trunks rather than foliage (New, 2005).

It certainly seems locally abundant, but this is a species with a British distribution which is not well understood. This shows the value of looking in places such as household timber stores and sheds where overlooked taxa may well be found. More about our firewood inhabitants soon...

Reference


New, T.R. (2005). Psocids. Psocoptera (Booklice and Barklice). RES Handbooks for the Identification of British Insects 1(7): 1-146.

Rollin' rollin rollin' - the diverse inhabitants of a willow leaf

Over the last year or so (yup,  the 'Ecology Spot' is nearing its first birthday!) I've posting several musings on the inhabitants of galls - not only the gall causers but also other species that can make galls their home. However, there is something conceptually similar, and closely related biologically, that I haven't looked at yet, and that is leaf-rollers.

Leaf-rollers, as the term suggests, are organisms that roll leaves to form shelters - unlike galls, the plant doesn't grow new structures, although there is some overlap (excuse the pun) with some leaf-rolls including further distortions such as thickening and increases in cell number, and hence being considered galls (Redfern & Shirley, 2011). In this case, the roll in a willow (Salix) leaf (found at Winnall Moors on the edge of Winchester, southern England) involves twisting and thickening of the plant tissues and so is classed as a gall (only just - sometimes the thickening is very slight).

Willow leaf roll showing twisting and thickening (increased cell size is visible in places)

 The downwards roll affects both sides of the leaf and most of the blade which indicates that it was caused by one of the Phyllocolpa species, a genus of sawflies in the family Tenthredinidae. Indeed, there were small dark sawflies with yellowish legs in the area which may well have been Phyllocolpa, although I did not manage to catch a specimen (either physically or photographically). As the larvae of these sawflies drop to the ground to pupate in the soil, it is not uncommon for galls to be empty, but the only way to find out is to look...

The roll unrolled - at first glance there is nothing but frass (invertebrate faeces)

Looking more closely, a few pale creamy-white rounded-oval eggs can be seen, each no more than 0.5mm in diameter. Whatever they are, an adult invertebrate was here recently. We'll return to these later...

A small cocoon of tangled silk. The lid (top right) is detached showing that whatever developed here has now left.

The bottom of the cocoon showing attachment threads plus a dark patch that may be frass.

So, we have eggs and an empty cocoon - is there anything more immediately identifiable? Well, fortunately yes. Whether or not they are in any way related to the cocoon I don't know, but two exuviae ('skins') were also present.

An unidentified exuvium - probably one of the Hemiptera (true bugs) with clearly defined wing buds and abdominal segments.

That's more like it - something recognisable, an exuvium of a small spider; even the leg hairs are clearly visible.

Although the 'bug' had long gone, the spider (or at least a spider) remained.

Dorsal view of the tiny spider (a few mm long) found in the leaf roll.

A close-up showing various appendages and some of the eyes.

Although the abdominal pattern seems quite clear, this is probably a juvenile. From the general form, I suspect it is one of the orb-weavers (Araneidae) though I would be more than happy if an arachnologist could clarify! If it is this family, it may be using the leaf roll for shelter as hunting takes place on an orb-web (a small one may have been present but un-noticed of course). Along with the spider I also found the following insect already dead (the abdomen was dry and wrinkled) - I wonder if it had become spider-food?

Ventral view of the insect showing the pointed 'snout', long antennae and spotted wings held in a tent-like position.

Dorsal view of the head showing protuberant compound eyes and orange simple eyes (ocelli). Note the patterning on the head and the bristly antennae.

This is a psocid or barklouse - the tented wings with spots at the tips of the wing veins, plus the habitat (on  foliage of trees and shrubs) make this a straightforward identification as the genus Ectopsocus. It is probably the common E. briggsi, but dissection is needed to separate it from E. petersi and E. meridionalis with ceryinaty, and the taxonomy of these closely related species remains uncertain (New, 2005). The protuberant, almost stalked, eyes mean it is probably a male.

And so, that brings us to the end of the specimens that could be identified (to some extent at least) at the time of collection about two weeks ago. However, I did mention that we would return to the eggs. Once found, I put them on their section of leaf in a small container to see if they would hatch, and they did...

Tiny larva about 1mm long - dorsal view

Ventral view showing segmented legs.

Ventral close-up of the head and thorax.

The dorsal view looks superficially somewhat like a woodlouse (i.e. it is 'onisciform'), but the darkened and hardened ('sclerotised') head with small pointed mandibles, plus the legs, show that it is actually a tiny beetle larva, one of two that hatched. It may not be immediately obvious, but this is actually a larva of a 'flea beetle', one of the small species of jumping beetles, the tribe Alticini within the family Chrysomelidae, although it might be within the wider subfamily Galerucinae within which the Alticini are included. The legs are short and have 4 segments (with a claw) and the mandibles are simple and sickle-shaped without a grinding surface ('mola'). There are thin bristles around the body (e.g. just visible top left in the 3rd photo) but no long cerci (tail-like appendages), the antennae are tiny and conical, and willows are a favourite host plant (Cooter & Barclay, 2006). Having just hatched, this is a first-stage larva and hence difficult to identify further, though van Emden (1942) is a standard work that is often useful for larval identification to family. However, the Macro-invertebrate Lab at the City Valley State University have kindly produced a Digital Key to the Aquatic Insects of North Dakota. They have good clear images of a more fully developed larva of this type, and also images of larva at genus level for Pyrrhalta - very similar to what was found here.

So, at present, I have identified all the organisms within this single leaf roll as far as I can. I hope it shows the importance of such small-scale habitats and the diversity they support, as well as highlighting some groups that are likely to be under-recorded due to their small size and tendency to hide. These under-recorded groups and habitats are worth taking the time to investigate as there are discoveries to be made that might be in your local patch of habitat or even your garden or back yard. Happy bug-hunting!


References

Cooter, J. & Barclay, M.V.L. (eds.) (2006). A Coleopterist's Handbook (4th ed.). AES, Orpington.
New, T.R. (2005). Psocids. Psocoptera (Booklice and Barklice) (2nd ed.). RES Handbooks for the Identification of British Insects 1(7): 1-145.
Redfern, M. & Shirley, P. (2011). British Plant Galls (2nd ed.). FSC, Shrewsbury.
van Emden, F.I. (1942). Larvae of British Beetles. III. Keys to the families. Entomologists' Monthly Magazine 78: 206-272.

What's in the box? No.5 - a shiny jewel and some uninvited guests.

My wife is beginning to recognise the signs. A jiffy-bag lands on the doormat and there's a small box or tube inside it - yup, a specimen has arrived in the post. This time it was expected as the collector had emailed in advance to ask if I wanted a specimen or two of the colourful Rosemary Beetle Chrysolina americana (Chrysomelidae) which he had found on Hydrangea plants in a garden centre in Gloucestershire. Hydrangea is not the usual host plant - it is generally found on rosemary, lavender, sage or thyme. Of the two specimens sent, one was still alive before being sent and arrived here still very active - it is now in a pot with some sage leaves while the other has been investigated for your reading pleasure...

Dorsal view of C. americana showing the colourful stripes and double rows of punctures. Length approx 7.5mm.

The area around the suture (where the wing-cases meet) showing punctures plus some fine sculpturing.

Ventral view.

The dorsal views show what a pretty beast this is - metallic stripes on a blue background. However, the ventral view shows something less welcome in the form of numerous white tufts.

Threads of mould, plus some larger lumps, growing on the underside of the beetle.

Mould growing underneath the wing-cases which have been spread apart. The triangular structure at the top is the scutellum.

This highlights a major problem with maintaining an insect collection - the avoidance of pests which can damage specimens. With a relatively large 'meaty' beetle like this, it is important to prepare specimens to prevent mould - for example they can be dried and some people add cloves to the drying chamber to help avoid fungal growth. The next step was to see how bad the damage was.

Dorsal view with wing-cases spread.

Although the focus isn't too clear, the abdomen can be seen to be hollow with the upper surface missing and with mould coating the inside. There may have been other invertebrates feeding on the beetle as well as fungal attack.

Looking closely at the underside of the head, as well as mould, a white oval egg can be seen in the centre, below the antenna.

So, there has been some invertebrate activity - this egg was just one of several so as you'd expect, I took a closer look...

One of the eggs (mag x400) showing some small bumps on the surface. The linear structures top right are fragments of fungal hyphae from the mould.

Searching the beetle more carefully, I eventually found something that could be responsible for the eggs - a hairy mite which I think is Glycyphagus domesticus (the Furniture Mite).The pale colour and long hairs are characteristic - it used to be associated with old damp furnishings where it fed on fungi that grew on stuffing etc. So, when the moist, freshly dead beetle began growing mould, it is likely that this mite arrived to feed on the fungus.

The mite (possibly G. domesticus) on the beetle.

Of course, I don't know for certain that the eggs come from this mite. However, with the specimen in no condition for adding to a collection, I've put it in a container to see if the eggs hatch and if so, what emerges. In the end, this is a tale about the importance of preparation and maintenance of insect specimens more than my usual bug-nerding. A web search for 'dermestes' or 'museum beetle' will provide you with many unhappy tales of entomological destruction. However I don't need to repeat these so, given that I have a microscope and a camera, I thought I'd finish with a couple of shots of fine morphological detail...

The inner surface of a wing-case showing the lack of metallic colour, but with the rows of punctures clearly visible.

One of the beetle's 'feet' showing tarsal segments bearing a sickle-shaped claw and a dense brush/pad of yellow hairs. There are also other hairs and some longer, sparser bristles.

When slime gets spiky: slime-moulds of the family Didymiaceae

Many people are familiar with slime-moulds to some extent, with the most popular view being of a slowly streaming patch of goo, sometimes brightly coloured, much like a large amoeba - possibly unsurprising as they are Protozoa even though commonly treated as honorary Fungi. Another comonly encountered form is the 'dog'd vomit' type which appears as a pale yellowish lumpy patch among grass, including garden lawns. One common and widespread example of this second type is Mucilago crustacea which does indeed look like dog's vomit when freshly emerged. However, within about a day, the cortex hardens and the spore mass darkens, by which time it may well have moved up the stems of grass or other plants, and become visually quite different.

The aethelium (combined spore-bearing structure) of Mucilago crustacea on the stem of a reed at Winnall Moors, southern England.

In the above picture, the dark grey-black spore mass can be seen on the left side and there is the remnant of cytoplasmic streaming beneath where the specimen has moved up the reed stem. The cortex (the surface covering the aethelium) is powdery and spongy and any movement was sufficient to send flakes and presumably spores into the air.

The cortex in close-up showing the spongy, almost brain-like, texture and powdery surface.

The reason for this texture is the presence of crystalline calcium carbonate which impregnates the structure of the slime-mould, with the cortex forming calcareous powder and flakes.

A mass of spores and calcareous crystals under x40 magnification. The dark circles are air bubbles, but note the scattered spores which appear as tiny brownish circles in transmitted light.

One of the masses under x100 magnification. A cluster of brownish spores can be seen bottom right, each being a little over 10µm in diameter. The calcareous crystals are a similar size and can be seen as small spikes to the left of the picture.

Given the presence of abundant calcium carbonate in the structure of this species, it is found most commonly in limestone-rich areas such as calcareous grasslands (Winnall Moors is a wetland on chalk) and is found only rarely in acidic conditions. The outer covering is coated with calcium carbonate in various forms (powdery, scaly, compacted and so on) in all of the Didymiaceae, the family which includes M. crustacea. The large genus Didymium has a powdery covering of star-shaped crystals which in some species may aggregate to form a crust; the shape and size of these crystals can also help to identify individual species. However, the taxonomy of this family is unclear and it is likely that genetic studies will redefine the boundaries between genera.

Reference

Ing, B. (1999). The Myxomycetes of Britain and Ireland: An Identification Handbook. Richmond, Slough. The current standard work on species in the British Isles.

Ladybirds and the fungus of love

If you go into a chemist/pharmacy, the range of creams like Canestan will tell you just how familiar humans are with fungal diseases, especially sexually transmitted ones. However, humans are not the only species to suffer from fungal STDs.

One taxonomic group which is host to a fungal STD unfamiliar to most people is the beetle family Coccinellidae, the ladybirds, lady-beetles or ladybugs. In late September I was doing some conservation work, cutting willow on the wetland nature reserve of Winnall Moors on the edge of Winchester, southern England. During this work, several specimens of the Kidney-spot Ladybird Chilocorus renipustulatus were found, a scattered but sometimes locally abundant beetle associated with willow on wetlands. So, no great surprise there. I took a photo and when I got home, added it to my list of species records and also decided to add it to the iSpot site. At this point I noticed the yellowish tufts attached to the rear - I had seen two or three individuals with such tufts in the field but only now did they become clear.

C. renipustulatus showing the tufts of what appears to be H. virescens on the rear of the elytra (wing cases).

I had no idea what they were (they looked like lichen but that seemed unlikely!) and made a note to investigate, though I didn't have a specimen. However, a few days later, one of the recorders from the UK Ladybird Survey posted a response stating that the tufts looked like the sexually-transmitted fungal disease Hesperomyces virescens (in the order Laboulbeniales). This was interesting enough as I'd never heard of it, but he also mentioned that it might be the first record of H. virescens on this species of ladybird. A shame I didn't collect a specimen! So, what is this fungus and what does it do?

All the fungi in this order are obligate parasites of arthropods (i.e. they need live arthropods) and derive nutrition via a 'haustorium' which penetrates the cuticle (Evans 1988). So, although they are ectoparasites (living on the outside of their host), they do penetrate the surface and H. virescens is in fact one of the few fungi in this order to have haustoria forming a number of narrow branches radiating out into the body cavity (Batra 1979). In work on the first record of this fungus on the Harlequin Ladybird Harmonia axyridis, Garcés & Williams (2004) noted that H. virescens was more prevalent in autumn after ladybirds had been through a period of aggregation/clustering. With my observation having been made in late September in the UK, this tendency may explain that a few fungal tufts were noted even though they weren't being sought.

Other ladybird species such as Adalia bipunctata (the Two-spot Ladybird) and Olla v-nigrum (the Ashy-Grey Ladybird) have been recorded as hosts of this fungus, while research into a relative of the species considered here, C. bipustulatus (Heather Ladybird), has shown that the fungus can cause premature death of the beetle (Kamburov et al. 1967). More recent work in the US (Riddick & Cottrell 2010) has suggested a preference for H. axyridis as a host with few instances of the fungus infected its 'original' host Hippodamia convergens (the Convergent Ladybird), a common and widespread species in North America. However, this research notes that H. axyridis was also the most abundant ladybird, hence the high rate of fungal infection could be due to the higher frequency of sexual/social contact between individuals (this was also seen in the native O. v-nigrum) - something which is reduced in less abundant species. Both H. axyridis and O. v-nigrum overwinter is mixed-sex aggregations, again supporting the idea that host and fungal abundance are connected. This may seem obvious in hindsight, but is important as it also links to possible effects due to differing activity levels.

For instance, Riddick & Cottrell (2010) also showed that of the two main host species, H. axyridis males had a higher infection rate than females, something not seen on O. v-nigrum. This suggests a possible behavioural effect with H. axyridis males behaving in such a way (they mount males as well as females when seeking mates) as to experience greater levels of exposure to the parasite. When Welch et al. (2001) proposed their sexual transmission hypothesis to explain the distribution of H. virescens thalli on ladybirds (they looked at A. bipunctata), this was because they noted fungal structures on the upper surface of females and the corresponding underside of males, mirroring the mating position. As physical contact may initiate spore discharge, the position of the fungus on a beetle's body may reflect the type of contact that occurred
(Weir & Beakes 1996). Thus, fungal infection rate may be affected by the rate of sexual/social contact as well as simply the abundance of hosts.

So, we have an overview of some aspects of the relationship between the fungus and several ladybird hosts, but what about C. renipustulatus? Well, initial indications are that there are no published records of this ladybird as a host of H. virescens. This may turn out not to be the case even though I have searched quite thoroughly as has 'rimo' at iSpot, but for now this appears to be a potential new discovery worthy of a visit to Winnall to collect specimens!

*** UPDATE ***
After feedback from mycologists, this find does appear to be a world's first as a new host for the fungus and has now been published as a short paper in The Coleopterist:

D. Hubble (2011). Kidney-spot ladybird Chilocorus renipustulatus (Scriba) (Coccinellidae), a new host for the parasitic fungus Hesperomyces virescens Thaxter (Ascomycetes: Laboulbeniales). The Coleopterist, 20 (3), 135-136 Other: 0965-5794

References

Batra, L. (1979). Insect-fungus Symbiosis, Nutrition, Mutualism and Commensalism. Allenheld, Osmun & Co., New York.
Evans, H.C. (1988). Coevolution of Fungi with Plants and Animals. Academic Press, San Diego.
Garcés, S. & Williams, R. (2004). First record of Hesperomyces virescens Thaxter (Laboulbeniales: Ascomycetes) on Harmonia axyridis (Pallas) (Coleoptera: Coccinellidae). Journal of the Kansas Entomological Society 77(2): 156-158.
Kamburov, S.S., Nadel, D.J. & Kenneth, R. (1967). Observations on Hesperomyces virescens Thaxter (Laboulbeniales), a fungus associated with premature mortality of Chilocorus bipustulatus L. in Israel. Israel Journal of Agricultural Research 17(2): 131-134.
Riddick, E.W. & Cottrell, T.E. (2010). Is the prevalence and intensity of the ectoparasitic fungus Hesperomyces virescens related to the abundance of entomophagous coccinellids? Bulletin of Insectology 63(1): 71-78.
Weir, A. & Beakes, G.W. (1996).Correlative light- and scanning electron microscope studies on the developmental morphology of Hesperomyces virescens. Mycologia 88: 677-693.

Welch, V. L., Sloggett, J. J., Webberley, K. M. & Hurst, G.D.D. (2001). Short-range clinal variation in the prevalence of a sexually transmitted fungus associated with urbanisation. Ecological Entomology 26: 547-550.