In an ecological investigation of the gall-forming aphid,Smynthurodes betae Westw., we discovered that more than 20% of the fundatrix galls were parasitized by Monoctonia pistaciaecola Stary (Aphidiidae). This is a new host record for this parasitoid. A Pteromalid hyper-parasite was identified as Pachyneuron? leucopiscida Mani. Ecological information on the parasitoid is provided, and the low frequency of parasitoids known from gall-forming aphids, compared with freeliving ones, is discussed.