Another Knapweed Gall Fly

Gall fly Chaetostomella cylindrica (Diptera: Tephritidae) on knapweed (Centaurea nigra). Similar to, but distinguishable from the Terellia tussilaginis that I saw on burdock (Arctium sp.) last year.

Last year I saw one of these flies on yarrow (Achillea millefolium) but, at the time, conjectured that it had just been blown off some nearby thistles.  Well, the above fly was in the same area so it seems more likely that last year's fly was blown off the knapweed onto the yarrow.

A few weeks ago I saw another species of gall fly, Urophora jaceana, on knapweed, but that was over in the Wilderness, quite a way away.

Photo taken in Whiteknights Park, Reading University grounds, Reading, UK, on 2010-07-04.