Martin, only Chlorion aerarium (first link) has antennae like my spotting, and it is found only from Mexico to the north. I'll keep looking for an ID, thank you very much for your help.
There seems to be more than one suspect for this spotting
http://insects.ummz.lsa.umich.edu/sphecidwasps/chlorion.html
http://www.bugpeople.org/taxa/Hymenoptera/Sphecidae/Chalybion_californicum/Chalybion_californicumPage.htm
http://www.flickr.com/photos/davidcory/3806361770/
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