It's June, and wasps are busting out all over

Bees are good. We like bees. They pollinate and are pleasant to watch. They are of course also wild creatures subject to the stresses that any other organism has to deal with, and one of these is parasitism. With our garden bee logs, new and old, almost completely occupied by the red mason bee Osmia rufa, it is not surprising that other nesting sites are sought out. Sometimes the chosen spot is not a good one, as in this case where a nest had been attached between a hoe and the inside of our tool shed - we'd noticed the nest, but the hoe fell down anyway, taking some of the cells and cocoons with it.

Osmia rufa nest - the open sides of the cells were pressed against the handle of a hoe until it fell down. Note the larva in the bottom centre cell (now taken away to be raised indoors)

The inside of an O. rufa cell - note the plug made of numerous small pieces of mud tamped into place by the prongs on the female's head.

A cocoon and pollen ball (larval food supply which includes a small amount of nectar) from an O. rufa cell.

Being a fan of bees (well, wildlife in general really) and ever-curious, I collected the cocoons that had been displaced (about a third of the whole nest) and brought them indoors to be put into a hatchery. I was of course hoping to see the bees emerge and release them, but a few days later something else happened entirely; the hatchery was full of small parasitic wasps - Monodontomerus obscurus (Hymenoptera, family Torymidae) - 21 in total.

Some of the Monodontomerus obscurus hatched from O. rufa cocoons

A female (note the ovipositor) M. obscurus apparently feeding on an O. rufa larval pollen store.

Although the larger parasites of O. rufa are listed in Baldock (2008), there seems to be relatively little mention of this aspect of the bee's natural history even though it is a familiar and popular species. However, Krunic et al. (2005) provide more detail and note that M. obscurus can suppress O. rufa populations in some nesting situations such as paper tubes and hollow reeds.

This is a normal part of bee ecology of course - and the wasps are interesting little jewels in their own right, so (as ever) I took the opportunity to have a look at one of them (a female) more closely. Males are present but smaller (approx. 4mm long without appendages, females approx. 5mm) and lack the ovipositor that female use to lay eggs into the bee cocoons.

Female M. obscurus - approx 5mm long plus 2-3mm of ovipositor

Close-up of the head of a female M. obscurus - note the red eye with short white bristles, plus the sculpturing on the head and thorax.

Close-up of the hind femur of a female M. obscurus - note the sculpturing on the leg and the 'finger-print' pattern of sculpturing on the abdomen behind it. Also, the edges of the thoracic plates bear fringes of short white bristles, presumably to protect the membranous joints.

O. rufa cocoon with M. obscurus exit hole.

With the cocoon having disgorged its parasites, there was only one thing left to do - open it up to what was left inside.

The content of an O. rufa cocoon after emergence of M. obscurus.

I did wonder of there would be much evidence of the juvenile bee, but very little was left, having presumably been consumed by the wasp larvae - there are a few fragments (e.g. bottom right) but nothing more. Most of the invertebrate material consists of pupal skins of M. obscurus - unsurprising given the number that emerged. There is some frass (faeces) and bits of dried mud from the nest which must have fallen in before the cocoon was spun. Top left is a dead female wasp who didn't emerge fully from pupation. She is of course also in a hatchery just in case she releases smaller parasites of her own...

References

Baldock, D.W. (2008). Bees of Surrey. SWT, Woking.
Krunic, M., Stanisavljevic, L., Pinzauti, M. & Felicioli, A. (2005). The accompanying fauna of Osmia cornuta and Osmia rufa and effective measures of protection. Bulletin of Insectology 58(2): 141-152.

Insect slaves in a fungal nation II

I've written about the fly-killing fungus Entomophthora muscae before, way back near the start of the Ecology Spot. In that post I covered the behavioural changes it causes, and a bit about how the fungus does this (or rather, how little we understand this). I don't want to repeat it here (it's all in the original post), but when I found another yellow dung-fly (Scatophaga stercoraria) infected with E. muscae, (well, certainly this fungal genus, and E. muscae is by far the most likely) this time in our garden, I felt an update was in order.

A dead yellow dung-fly Scatophaga stercoraria infected by Entomophthora muscae. Note the typical posture adopted shortly prior to death - head down, abdomen up, wings spread - this maximises the spread of fungal spores.

With the Harvard research programme (looking at how the fungus infects hosts and changes behaviour) having closed, it does not seem that this thread is being actively pursued at present (if this isn't the case, please do let me know and I'll update this post). There has however been recent work looking at the evolutionary history of the fungus (e.g. Gryganskyi et al. 2013) and taxonomic research by Humber (2012) raises the group to full phylum status.

More on this fascinating, if often overlooked, fungus undoubtedly to come...


References


Gryganskyi, A.P., Humber, R.A., Smith, M.E., Hodge, K., Huang, B., Voigt, K. & Vilgalys, R. (2013). Phylogenetic lineages in Entomophthoromycota. Persoonia 30: 94 -105.

Humber, R.A. (2012). Entomophthoromycota: a new phylum and reclassification for entomophthoroid fungi. Mycotaxon 120: 477-492.

Murk-dwelling bottom-breathers

I've posted about our garden pond before, but may not have mentioned that off to one side of it is an old stone fountain-top which has been plugged to provent leaking. Having no outflow unless there is heavy rain and it spills over, this means it becomes stagnant with leaves and other organic matter accumulating. The temptation might be to clean this out and add clean water, but no, it is there for a reason - habitat for larvae that are adapted for such conditions. An example of this is the rat-tailed maggot, the larva of hoverflies in the genus Eristalis, in particular E. tenax, and others such as the sun-flies Helophilus sp., plus Sericomyia, Mallota, Anasimyia and Myathropa. As adults, Eristalis are are excellent honey-bee mimics (hence the common name of 'drone-flies'), but their larvae, like those of the other genera listed, are very different. The most obvious feature is the long, telescopic posterior breathing tube - essential when living in stagnant, low-oxygen water among decaying vegetation.

Rat-tailed maggot, the larva of Eristalis sp. (probably E. tenax), approx. 10mm long excluding 'tail'.

This is a young larva - my identification is a little tentative as I can't see the key features yet, but the timing is right as E. tenax were frequenting the water long enough ago for eggs to now have hatched, whereas although there are Helophilus pendulus as well, they have only just started breeding activity as far as I can tell; I will be able to confirm their identity when they are more fully developed. They are filter-feeders and some of the gut contents are visible here, as are the well-developed prolegs.

Rat-tailed maggots showing how their breathing tubes are used.

The white section of the tube forms a sheath made from one extended segment and contains complex musculature used to extend and retract the breathing tube, as well as protecting it (the tip of the tube can be seen as a short white-tipped dark segment). The larvae can also swim slowly by undulating the body and tube. They may not be the most attractive creatures, but I do think they are interesting, and they are of evolutionary interest as these larval forms appeared quite recently in hoverfly evolutionary history (Rotheray, 1993), not to mention their role in consuming waste organic material. They do of course also develop into adults - the dronefly mentioned above, which has a role in pollination, so a valuable species too.

Eristalis adult on Buddleia davidii

Reference

Rotheray, G.E. (1993). Colour guide to hoverfly larvae (Diptera, Syrphidae). Dipterists Digest 9: 1-156.

Leaf-cutters and cuckoos

I've written quite a few posts about bees, especially garden species  (search for 'bees' on this blog and you'll see!), but having found around 20-25 species so far, there is plenty more to look at. For instance, yesterday I noted a small-to-medium stripy bee being chased away by a leaf-cutter. Naturally, I grabbed my camera and watched what was happening. The smaller bee turned out to be quite an interesting species...

Male Coelioxys rufescens

I was interested to see a species of Coelioxys in the garden as none of them are especially common in Britain. They can be difficult to identify, although there are only seven species in this country and two are coastal, so the options are limited. This one is a male - the abdomen is blunt with short spines whereas the female has an elongtae pointed abdomen. Also, the species are all cuckoo bees ('cleptoparasites') which means they take over cells in the nests of their host bees, all of which are in the genera Megachile and Anthophora. They do this by the female using her elongated abdomen to cut into the host cell and lay an egg through the hole. Young Coelioxys larvae have long, curved jaws which they use to destroy the host egg or larva; they then feed on the food stores of the host, with later instars (larval stages) having normal jaws.

C. rufescens is fairly widespread in south and SE England (scattered further north), though Coelioxys species may be under-recorded; I have recorded it in our garden in previous years, as well as one of its possible hosts, the leaf-cutter bee Megachile centuncularis - there are several others noted in Collins & Roy (2012) though the full host range is uncertain. It flies fairly early (from June) for a British Coelioxys (along with C. elongata); most are not active until July.

Megachile centuncularis approaching a common bird's-foot trefoil (Lotus corniculatus)

Megachile centuncularis feeding on a garden thistle (Cirsium sp.)

If M. centuncularis is a host of C. rufescens, this might explain the aggressive behaviour seen, with the parasitic species being repeatedly chased away (though not a nest/host-searching female). Host-parasite interactions can be fascinating and tell us much about evolutionary processes - for example, some cleptoparasites may mimic chemical cues to avoid anti-parasite strategies (e.g. Strohm et al., 2008), and it seems reasonable to suggest that hosts can detect their parasites. This of course does not confirm that M. centuncularis is a host species, but it a good indication that it is something worth investigating more closely...


Reference

Collins, G.A. & Roy, H.E. (eds.) (2012). Provisional Atlas of the Aculeate Hymenoptera of Britain and Ireland. Part 8. BRC, Wallingford.
Strohm, E., Kroiss, J., Herzner, G., Laurien-Kehnen, C., Boland, W., Schreier, P. & Schmitt, T. (2008). A cuckoo in wolves' clothing? Chemical mimicry in a specialized cuckoo wasp of the European beewolf (Hymenoptera, Chrysididae and Crabronidae). Frontiers in Zoology 5(2). [online] [accessed 06/06/2013].

One man and his wasp-shed

I often write about invertebrates found in our back garden, for various reasons - finding them is convenient, I'm often here, and they are a good indication of the interesting species that may arrive if a garden in managed in a wildlife-friendly way. I'm used to finding spiders in the shed, dead-wood invertebrates in the wood-store and so on - however, I wasn't expecting to find this...

An insect nest in our toolshed - probably made by a mason wasp (subfamily Eumeninae)

The nest is wedged between the door-frame of the shed and a long hoe-handle hooked above it. Each cell (there are about 10-12) is around 1cm in diameter but apart from that, no clues as I haven't seen the insect that made them. However, the overall form is, I think, like those made my some mason wasps (Family Vespidae, subfamily Eumeninae) and I have seen a few in our garden in previous years. One of the 'mud-daubers' in the genus Ancistrocerus seems a reasonable guess, but I'll have to wait and see what appears and will definitely investigate the nest closely after emergence. Each cell should have prey items inside for the larvae to feed on  - these can be from a wide range of other invertebrates. I will also look out for the smaller jewel wasps (Chrysididae) as these are parasites of eumenines, and I have also seen a few of these using our garden. Should I see anything interesting, this is where you'll read about it!