Posted by
Zeegers on 30-10-2006 09:12
#2
And, to add to Chris, the reddish spot on thorax before scutellum are a typical 'jizz' for C. rasa.
By the way, the headshot is from a male !
Unless I'm very mistaking.
Theo
Posted by
ChrisR on 30-10-2006 10:38
#4
Yeah, the frons looks exceptionaly narrow for a female. From the Central European key (again assuming that it really does have a yellow basicosta and 1 anterodorsal on the mid tibia):
bombylans: Frons 0.53 - 0.61x as wide as one eye in males, 0.63 - 0.71x in females
rasa: Frons 0.42 - 0.50x as wide as one eye in males, 0.47 - 0.58x in females
puberula: Frons 0.64 - 0.72x as wide as one eye in males, 0.72 - 0.87x in females
But it is a very tricky measurement to get right first time - I have tried it with several experienced dipterists and it took a few goes to get the technique consistent. You really have to look down on the head perpendicularly from above. Then I usually use my zoom and a graticule to make the frons exacty 1 or 2 marks wide - then compare with the clearest eye - allowing for the drift in focus as you look for the widest point
Would be
very interesting to know if it is really a female and it has measurements less than is normal for
C.rasa.
Just another thought: they are freshly emerged so it might be worth waiting until they are dead and dry before measuring them. By that time the head may have changed shape a little. That's one important thing to remember - keys are always made from dead material, not from photos of living flies!
Posted by
ChrisR on 31-10-2006 00:41
#6
No
But I'd like to know if anyone else knows! Theo?
I am not sure if it always happens either but every time I have seen reared material it has always been the same sex.
(it's very unlikely I'll see any Tachinidae until late March 
)