Summary

Species introductions are a major issue for biodiversity conservation and human well-being worldwide, but their impact can be particularly severe in oceanic island ecosystems. Here, we report the occurrence of two alien species on Terceira island, Rivellia syngenesiae (Fabricius, 1781) (Diptera: Platystomatidae) and Sceliphron caementarium (Drury, 1773) (Hymenoptera: Sphecidae), being the first reports of these insect families to the Azores archipelago. We provide the diagnosis of each species, information on their distribution and ecology, and discuss their potential impact on native biodiversity. Furthermore, we anticipate the spread of these species through the Azores islands, benefiting from the high increase in commerce and tourism, and stress the need to set a program for the early detection of alien species in the archipelago.