Sunday, 17 August 2014

The Bee and the Wasp

Back in November 2012, the bird-banding at our regular site at The Charcoal Tank Nature Reserve, not far from West Wyalong in central-west New South Wales, was keeping us occupied if not busy, and I had time to follow the activities of several solitary bees that I was not aware of having noticed on any previous trips.

Throughout the Saturday (3 Nov 2012), single bees were seen hovering low over the bare dry ground around our banding station. After what seemed to me a fairly prolonged inspection, the bees would decide that one spot that looked pretty much like any other spot was a good place to initiate a burrow. I don’t now recall how long they spent excavating these burrows, but by the end of the day there were probably 5 or 6 burrows scattered about in the immediate vicinity of our banding tables.

A solitary bee hovering just above the ground, looking to excavate a burrow.

When seen from above, the inspecting bees were clean and attractively patterned with white banding on the abdomen, a buff furriness to the thorax, and a yellowish face. It was this colour scheme, and their persistent hovering behaviour just a few inches above the ground, that drew my attention to them.

A solitary bee relocating its burrow.

As their burrowing continued the bees became progressively drab and dusty.

A solitary bee in the early stages of burrow excavation.

A solitary bee in action excavating its burrow

The bees became more and more dusty as the burrowing progressed.

The following day, the bees had essentially disappeared (though there was at least one still finishing off an excavation), and instead a brightly coloured wasp was seen hovering about in their place (there may have been more than one – I can’t clearly recall).

But it was clear to me from the general shape of these wasps that they were a type of parasitic wasp of the Evanioidea superfamily, and it didn’t take long to realise they were interested in the bees’ burrows. The implication being that these wasps parasitise the bees by laying their own eggs in the bees' burrows, to hatch and avail themselves of the food store provided by the bee for its larvae, or to feed on the growing bee larva itself. The host specificity of such interactions can sometimes be quite tight.

This parasitic wasp was hovering about in the same area the solitary bees had been the day before.
(Pseudofoenus sp. Hyptiogastrinae, Gasteruptiidae)

I spent several minutes watching and photographing one of these wasps sussing out one of the burrows, but then had to leave to check the mist nets for birds and didn’t pursue the vaguely Aesopian story of the bee and the wasp any further.

The wasp homed in on one of the solitary bee's burrows...
(Pseudofoenus sp. Hyptiogastrinae, Gasteruptiidae)

... landed, and spent quite a while "smelling" the burrow entrance with its antennae...
(Pseudofoenus sp. Hyptiogastrinae, Gasteruptiidae)

... before finally entering head-first into the burrow.
(Pseudofoenus sp. Hyptiogastrinae, Gasteruptiidae)

But more recently, and since starting this blog, I’ve been inspired to do a bit of research on these two and their interaction (ain’t the web a wonderful thing).

It turns out that the wasp is a species of Pseudofoenus, which is one of two genera (the other being Hyptiogaster) in the subfamily Hyptiogastrinae of the family Gasteruptiidae (which is indeed in the superfamily Evanioidea).

According to the CSIRO website ( ) the “Gasteruptiidae are one on the most easily recognised families of parasitic wasps. They are particularly distinctive because of their slender subclavate metasoma, the dorsal articulation of the metasoma to the propodeum, the elongate neck-like propleura, and expanded hind tibia.” - I think this means they have a thin machete-shaped abdomen that hinges out from near the top of the thorax rather than lower down, and have fat hind legs.

Pseudofoenus sp. (Hyptiogastrinae, Gasteruptiidae) at Charcoal Tank Nature Reserve, NSW.

Pseudofoenus sp. (Hyptiogastrinae, Gasteruptiidae) at Charcoal Tank Nature Reserve, NSW.

My Google-searching led me not only to Pseudofoenus, but also to a guy called John Jennings at the University of Adelaide who is a specialist on these wasps and has done a fairly comprehensive review of the genus. I got in touch with John and he kindly confirmed that my photos were of a Pseudofoenus species, but that “there are still many undescribed species”, and that he’d be happy to receive a specimen in alcohol if I was to see them again. Not sure what this means with respect to my wasp, but I certainly couldn’t find any images on the web that looked anywhere near as bright or with as much yellow as this one. Most are a dark reddish-brown in colour.

It seems the genus Pseudofoenus has a fairly restricted Gondwanan distribution with the majority of species being endemic to Australia (66 described so far), particularly the south-west, with others found in New Guinea and New Britain (5 species), New Caledonia, New Hebrides and Fiji (2), New Zealand (4), and South America (2 species).

So much for the wasp; what about the bees?

Despite a fair bit of effort, I haven’t really been able to narrow down the options at all well. I haven’t found anything that looks specifically like these bees, but did find lots of images of lots of bees, even from different families, that looked sort of similar. And my inexperience precludes me from being able to discriminate between or weight the possibilities. L

A solitary bee, most likely from either Stenotritidae or Colletidae families. 
(Postscript: this is most likely a species of Stenotritus - see below.)

John Jennings and Andrew Austin, in their 2002 review in Invertebrate Systematics ( ), state that “The hosts of very few species have been determined, but the few available records indicate that members of Pseudofoenus s.l. are predator-inquilines of colletid, halictid, masarine, and stenotritid bees.”

I think I can eliminate Halictidae, and Masarinae (which are the pollen wasps, a subfamily of Vespidae rather than bees), but Colletidae and Stenotritidae are still options. On balance, I’d like to think my bees are stenotritids (giving the option of either Stenotritus or Ctenocolletes), but I’d love to hear from anyone who might be able to give me a more definitive identification.

So this story doesn't really have an end, but I do wonder how tight the specificity these wasps might have for these particular bees is?

POSTSCRIPT (September 2014)

Subsequent to posting this article I made contact with Associate Professor Michael Schwarz from Flinders University in South Australia (a bee expert suggested by Dr David Yeates, Director of the Australian National Insect Collection - thanks David), as well as Dr Remko Leijs, Honourary Research Fellow at the South Australian Museum (thanks to John Jennings for this suggestion). Both were of the opinion that the bee in question is a species of Stenotritus. Specimens would need to be taken to attempt a more detailed ID, but both also made the point that there are likely many species that remain undescribed. 

So there is certainly a possibility that both the wasp and the bee are as yet undescribed species. I’ll certainly bee keeping (groan - sorry!) an eye out when bird banding at Charcoal Tank over the coming season...

POSTSCRIPT 2 (November 2014)

On the weekend of 14 -16 November I was back out at Charcoal Tank Nature Reserve for bird banding. The weather was rather extreme – 42 degrees when we arrived about 1:30 pm on Friday, dropping to 22 degrees by the following evening, and rain all Saturday night.

The rainfall patterns over the three months leading up to this weekend were very dry and quite different to those of two years previously when I last saw the bees, so I wasn’t overly optimistic of seeing them again. Nevertheless, after no sign of them in the heat of Friday afternoon, on the Saturday afternoon, about 2 pm, we did see a single stenotritid bee hovering over the same area where I’d seen them before. A bit later a second bee was seen. They seemed a bit more wary than last time, but perhaps that was because there were more people about and we were stationed slightly closer to where they were hovering.

Anyway, the short of it is I managed to collect one of these bees. I was reluctant to try for the other one as they don’t appear to be very numerous.

The bee is currently at home in the freezer in ethanol, but will be sent to Michael Schwarz to be included in some bee sequencing work by a past honours student over the coming months. Stay tuned...