Lysiphlebus testaceipes (Cr.), an exotic aphid parasitoid, but widespread along the West Mediterranean and Atlantic coastal areas, was regularly found in the northeastern part of the Iberian Peninsula parasitizing several aphid hosts, inland and in the Pyrenees. It was found, that the environmentally induced restriction of available host species together with the opportunistic response and host alternation of the parasitoid contributed to the successful and on-going expansion and establishment of L. testaceipes from the coast to the inland montane areas of the Iberian Peninsula. Also, a comparison of the overall host range of L. testaceipes in several areas of the West Mediterranean/Atlantic (southern France, Spain, Portugal) demonstrated a rapid increase in the host range in these areas. Parasites diseases and disorders; Parasites; Insect parasites; Hosts; Insect hosts; Land zones; Palaearctic region; Eurasia; Europe Lysiphlebus testaceipes (Aphidiidae); Hemipteran hosts; Aphidoidea; Spain; Opportunistic changes in host range & changes in distribution Aphidoidea; Hymenopteran parasites; Lysiphlebus testaceipes; Host range, opportunistic changes & changes in distribution; Spain; Hymenopteran parasite distribution & host range, opportunistic changes none