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Hai Benoit,
The first specimen (3 pictures) is most certainly a Conops flavipes. Black and yellow, scutellum half black half yellow, femur 3 yellow at base, with broad black ring in tophalf. This is a female. Especially in the second picture, from the side, the genital organ is very clearly visible. Nice pic!! The species is quite common. Known hosts are Bombus lapidarius, Osmia spec. and Vespula rufa
The second one is most likely Conops scutellatus. Characteristics are the silvery stripe on the side of the thorax, the yellow scutellum and the black stripe running from the base of the antennae to the frons (just visible in the picture) Known host is Vespula vulgaris
Greetings