New invader, old neighbour or new species? The curious story of the aphid Longicaudinus corydalisicola (Tao, 1962) (Hemiptera: Aphididae)

Determining the geographical origin of a species is usually a difficult matter. Regarding aphids, there are many cases in which species have been described when found outside their original distribution areas. Citizen science can help to find and monitor them, while molecular analysis aids with their identification. However, this kind of study has limitations. In this work, we present a clear example of these difficulties. An aphid species, which initially could not be identified based on its morphological characteristics, had been recorded on species of Fumaria in the Iberian Peninsula. Subsequently, it has been found in native spontaneous cover crops in citrus orchards in Valencia and in other natural areas of Spain. Thanks to citizen science its presence could be confirmed also in Portugal and France. The analysis of the molecular sequence of the cytochrome oxidase I gene (COI) highlighted a match with a species native to Southeast Asia, Longicaudinus corydalisicola (Tao, 1962). The molecular identification was then confirmed by morphological studies. We carried out a comparison between morphological descriptions available in the literature and the Iberian samples. Colonies were monitored during 2023 and 2024 in the Eastern areas of the Iberian Peninsula to determine the species population dynamics. Its status, possible origin and presence in Europe, in an area far from its known distribution area to date, are discussed.