Journal archives for June 2022

13 June, 2022

Key to the Didea, Dideomima, Asiodidea and Megasyrphus of the World

These are the Syrphine genera with a dipped radial vein.

This has been a bit of a challenge, but quite a lot of fun. Use this key with caution of course, some of these species are very poorly known, others very variable. The genus Didea in particular I think needs revision, and who knows if geographic variation is hiding distinct species currently under the same name?

Anyway, I hope at least this disseminates some information about these rather nice species.

Posted on 13 June, 2022 22:54 by matthewvosper matthewvosper | 3 comments | Leave a comment

27 June, 2022

Distribution of Colour Forms in Volucella bombylans

In iNaturalist we are able to identify the named colour forms of Volucella bombylans.

I have tried to add these to as many V bomblylans observations as possible to see if anything interesting emerges. Because a great many of these observations are not yet Research Grade at the level of 'form' the data below are taken for searches including any ID of that form using the "ident_taxon_id =" URL.

The forms are:
f. bombylans - all black haired but for a red haired tail.
f. plumata - yellow haired around the sides and back of the scutum, and the base of the abdomen, with a white tail.
f. haemorrhoidalis - as plumata but with a red tail.
There are other rare forms that are unnamed.

Conventional wisdom is that f. plumata is the most common form with about 2/3 prevalence, f. bombylans constitutes almost all the rest. This is borne out in iNat data: of 1387 observations 883 are f. plumata (64%), 451 f. bombylans (33%) and just 53 f. haemorrhoidalis (4%).

However they do not appear to be evenly distributed. I haven't looked for any research on this, so it's perhaps likely things are already known, but I thought I'd put them out there anyway.

f. plumata

f. bombylans

f. haemorrhoidalis

According to the iNat data, it would seem that f bombylans is quite restricted to the area between the Pyrenees (or really central France) and the Urals.

There are no f. bombylans observations in Asia, compared to 21 f. plumata and 1 f. haemorroidalis (one would have expected about 7).

There is only one f. bomblyans observation southwest of a diagonal line across France from St Malo to St Tropez - that is on the West coast of France. None at all in Iberia - again one would have expected about 6 or 7 from 19 Iberian observations.

The other interesting thing about Iberia is the overrepresentation of f haemorrhoidalis. The Iberian observations break down as 12 f. plumata and 7 f. haemorrhoidalis, that is very similar to the 2:1 ratio normally observed between f. plumata and f. bomblyans, as if f. haemorrhoidalis somehow replaces f. bombylans in Iberia.

There are also no f. bombylans in Scotland, out of 25 observations.

The numbers are fairly small and I've done no statistical analysis of the significance of this, but it certainly seems quite interesting.

Posted on 27 June, 2022 13:58 by matthewvosper matthewvosper | 7 comments | Leave a comment