Mountain Alcon Blue

[owen figgis]

I've recently returned from a very rewarding trip to France. Due to the timing of my previous visits I had not seen mountain alcon blue (or found it's food plant the cross leaved gentian), and this was near the top of my must see butterflies list. I had spent several days in the Vanoise area and had no success until I chanced upon a colony of the butterfly at 2050m on a south facing steep dry slope.

The females were egg laying on what appears to be a different type of gentian.

The only reference I can find regarding alternative food plants is in Tolman and Lewington where they mention G.germanica and G. asclepiadea. Neither of these look similar to me. A couple of days later I found G. cruciata covered in ova growing in a pasture within woodland at about 1300m.

There were no butterflies here but I found one spent female in an adjacent field.

[Padfield]

Very interesting. I agree, that doesn't look like cruciata, or either of the other stated European foodplants.

I've never seen females lay on any plant other than cruciata but have found the species away from any evidence of this gentian and had wondered if perhaps another hostplant was being used. My Russian books indicate at least one further species of gentian (G. kirilowii) and even a Dianthus (superbus) so it maybe its tastes are more eclectic than we normally give it credit for. Definitely something to keep an eye on next year!

Guy

[owen figgis]

The plant was quite small and difficult to find. The butterflies had no trouble locating it though and I found several plants within a radius of about 30m by following the females. Each one had a few eggs attached.

[Sylvie_h]

Hi Owen, Guy,

This is interesting as I have had the same experience a couple of years ago when I was in the Jura (1100m), I was really surprised to see a female Mountain Alcon blue laying eggs on Gentiana Lutea (giant yellow gentian). They could be using different kinds of gentiana when cruciata is not available.
Sylvie

[owen figgis]

I've found a better image of the mystery gentian. There must be someone on here who can name the species.

[David M]

I emailed my botanist friend who said, on the basis of the photo alone:

I think its Gentianella campestris, Field Gentian. Would have been easier to confirm with flowers. However you can see the two broad, prominent lobes to the calyx, enclosing the 3 narrower inner ones

.

Hope that helps.

[owen figgis]

Thanks David for the ID. I looked it up and the leaves certainly look similar - we even get this species in Scotland.

[Pieter Vantieghem]

In fact the initial description of "Maculinea rebeli" comes from a location above the height G. cruciata can be found and recent studies in Austria indicate Gentianella species to be the food plant of those populations, see http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4023245/

[owen figgis]

Interesting reading Pieter. The habitat and altitude was similar to the colonies studied in the paper - It seems likely that the food plant will be the same too.

[Pieter Vantieghem]

I guess the authors could be interested to hear about your findings, David Nash of University of Copenhagen will probably be interested as well (see talk 11-1 of the future for butterflies congress last spring: http://vlindernet.nl/doc/future4butterf ... f_2016.pdf)