Hi Margaret!

Many thanks again for your email. I'm glad to tell you that as a result of
joining this forum I have now collected 10 spherical galls on thistles and I
shall have a good look at them. No doubt I shall come back...

As for the attack of U. cardui on Solidago, anybody who would want to take this
up could easily test in the laboratory whether they could resist the temptation
to oviposit or not.

In the place where I collected my galls, Tommy Thompson Park, Toronto, goldenrod
is the predominant plant; I do not recollect seeing masses of thistles; but I
did find a galled one close by, see http://bugguide.net/node/view/356719. And
this poses yet another question. Why were the flies so *tempted* to do it?
Moreover goldenrod stems in the winter stay upright. It is indeed all very
puzzling.

Best regards,


Maria




--- In british_galls@..., M Redfern <m.redfern@...> wrote:
>
> Maria,
> Urophora females do have a telescopic ovipositor but its tip cannot actually
> pierce, I think. But it can push the eggs deep into a bud. Other species
> (Urophora stylata, U. jaceana) lay a clutch of eggs into young flower heads,
> inserting them between the bracts so they end up on top of the young florets.
> Eurosta belongs to a different tribe so perhaps it's not surprising that its
> behaviour is different.
>
> In UK, U. cardui is specific to Cirsium arvense so it is very surprising that
is
> can attack Solidago in the US. Perhaps C. arvense was very rare in the site
you
> collected your specimen from in that year, so it laid on goldenrod 'in
> desperation'!?
>
> With good wishes,
> Margaret
>
> Quoting MARIA <mariafremlin@...>:
>
> > Margaret,
> >
> >
> > Ah! Thank you very much for this very important piece of information. Now I
> > understand why the U. cardui galls have several larvae in one gall.
> >
> > So this is a very important difference between this species and Eurosta
> > solidaginis, both in the same family, Tephritidae.
> > The latter has a piercing ovipositor and uses it to pierce young leaf buds
of
> > Solidago species. The larvae then travel down to the stem and form
> > *individually* occupied galls. Stems sometimes have two galls but the
> > majority has just one because there seems to be a high mortality rate.
> > There is a very good video of a E. solidagines ovipositing; to see it visit
> > this page http://www.facstaff.bucknell.edu/abrahmsn/solidago/main.html and
> > click on "Streaming Video".
> >
> > Now I'm pretty sure that my U. cardui did emerge from one gall only. The
> > other one that I had in the same bag is a bit of a mystery though... See
> > http://bugguide.net/node/view/371857
> >
> >
> > At the time, of course, I was totally ignorant of all this. Then I though
> > that the flies were E. solidagines and had a great shock when more than one
> > month later I discovered their true identity. Since then I've entered a
steep
> > learning curve. Fascinating!
> >
> > Thanks again for your interest,
> >
> >
> > Maria
> >
> >
> > --- In british_galls@..., M Redfern <m.redfern@> wrote:
> > >
> > > The adult doesn't have a piercing ovipositor so can't drill a hole. She
> > lays a
> > > group of eggs into an axillary bud, pushing them between the small leaves,
> > and
> > > then the hatchling burrows into the stem - and its tunnel enlarges as the
> > gall
> > > grows. Air has got to enter the larval chamber otherwise the larva doesn't
> > > pupate, and I suppose it seeps in through this tunnel.
> > > Margaret
> > >
> > > Quoting philippe brunod <philippe.brunod@>:
> > >
> > > > I don't understand the origin of the tunnel to the surface.
> > > > There is the hole drilled for the ovopositon, but it's not that.
> > > > Is it the larva that hollowed this tunnel for it's future outcome ?
> > > >
> > > > Philippe
> > > >
> > > >
> > > >
> > > >
> > > > Original Message -----
> > > > From: M Redfern
> > > > To: british_galls@...
> > > > Sent: Tuesday, February 16, 2010 3:02 PM
> > > > Subject: Re: [british_galls] Urophora cardui winter galls
> > > >
> > > >
> > > >
> > > > Urophora cardui larvae cause chambers that are not sealed over - a
> > tunnel
> > > > to the
> > > > surface remains, usually stuffed with chewed up debris. In order for
> > the
> > > > fly to
> > > > emerge successfully as an adult, the gall has to fall to the ground
> > > > (usually in
> > > > the autumn) and rot a bit so that the fly is able to push its way out.
> > So,
> > > > the
> > > > gall tends to fall apart. If the gall remains on the plant above the
> > > > ground
> > > > this often means it doesn't rot and so the larva doesn't pupate or
> > emerge.
> > > > Hope this is useful,
> > > > Margaret
> > > >
> > > > Quoting MARIA <mariafremlin@>:
> > > >
> > > > > Hi!
> > > > >
> > > > >
> > > > > I have just joined this group. I've got a very amateurish interest
> > in
> > > > galls,
> > > > > mainly, I find them fascinating.
> > > > >
> > > > > As I have never seen overwintering U. cardui galls I would I like to
> > ask
> > > > you
> > > > > a couple of questions.
> > > > >
> > > > > 1. Do the larvae prepare exit tunnels before entering winter
> > diapause,
> > > > and,
> > > > > if so, do they leave the skin intact?
> > > > >
> > > > > 2. Does anybody have any photos of the galls after the flies have
> > > > emerged?
> > > > > Do they leave clear emergence holes?
> > > > >
> > > > > Best regards,
> > > > >
> > > > >
> > > > > Maria
> > > > > Colchester, Essex
> > > > > http://maria.fremlin.org
> > > > >
> > > > >
> > > > >
> > > >
> > > >
> > > >
> > > >
> > >
> >
> >
> >
>