Alien insects to the Maltese islands : the classification of alien taxa according to EICAT

Abstract

Europe is home to approximately 1,400 alien insects, hence the research and knowledge gathering on alien insect species and their impacts on biodiversity is of utmost importance, not only to implement effective mitigation and eradication measures but also to establish preventative strategies that reduce the risk of new introductions. In Malta, information about alien insects is scattered across various publications, complicating efforts to assess their diversity. The country has experienced significant biodiversity challenges from new introductions which became established and invasive, such as the Red Palm Weevil (Rhynchophorus ferrugineus), which has devastated palm trees (such as Phoenix canariensis), and the Castilloa borer (Phryneta leprosa), which has severely impacted black mulberry trees (Morus nigra). The aim of this study was to conduct an extensive literature review to compile a comprehensive list of alien insects reported in the Maltese Islands, and to perform an Environmental Impact Classification for Alien Taxa (EICAT) analysis for 12 species from the list. For the first objective, 319 alien insect species were documented, with the most represented orders being Coleoptera, Hemiptera, and Hymenoptera. Of these 319 species, 214 were categorised as established. Most species (255) had a known native range, while the remainder (64) were classified as cryptogenic. Among those species with a known native range, 107 species were traced to Asia, followed by North America (62), Africa (54), South America (42), Oceania (23), and Europe (3). For the second objective, an EICAT analysis was conducted on 12 established species in Malta. Due to limited local data on their effects on native biodiversity, studies from other countries were also used to inform the analysis. The results showed that five species caused moderate impacts on native biodiversity, signifying population declines without leading to extinction, one species caused minor impacts, signifying an effect on the individual, while five species were categorised as data deficient, indicating insufficient information to determine their precise impact. Finally, the Argentine ant (Linepithema humile) was classified as having a major impact, as it has caused population extinctions. Through this study it was also determined that EICAT faces challenges due to its reliance on subjective interpretation, particularly in literature searches, confidence ratings, and impact mechanisms, with issues such as incomplete literature vetting, language barriers and the exclusion of socio-economic impacts, affecting comparability and reliability.