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C. cylindrica has a very broad range of host plants John.

In my surrounding I saw it oviposit in Carduus sp. and in Centaurea sp.

I have no knowledge at all of dna, so I can't give you any advise about a dna-test.

Here is an interesting article about the whole matter :

https://www.researchgate.net/publication/24020840_Host_races_in_Chaetostomella_cylindrica_Diptera_Tephritidae_genetic_and_behavioural_evidence

Ben