The chalcid wasp Leucospis affinis has been known to parasitize only megachilid bees. Its rare occurrence as a parasite of the eumenid wasp Ancistrocerus antilope indicates that eumenid wasps may be a large resource this chalcid is not exploiting.
Cowan, David P.
"Parasitism of Ancistrocerus Antilope (Hymenoptera: Eumenidae) by Leucospis Affinis (Hymenoptera: Leucospididae),"
The Great Lakes Entomologist: Vol. 19
, Article 7.
Available at: http://scholar.valpo.edu/tgle/vol19/iss3/7