Adaptation of the invasive western conifer seed bug Leptoglossus occidentalis to Trentino, an alpine region (Italy)

Non-native organisms can affect native communities and ecosystems in different ways. We examine here the case of the western conifer seed bug Leptoglossus occidentalis Heidemann (Heteroptera Coreidae), a polyphagous pest of conifer seeds, introduced from northern America into Italy in 1999 and then spreading across the whole Europe. The bug was detected in alpine forests of Trentino (northern Italy) in 2002, and since then known mainly as a nuisance agent for its habit to overwinter inside buildings. The lack of information on the ecology in mountain areas led us to investigate its distribution in some alpine pine stands, in relation to altitude and to fungal pathogens potentially associated. The presence of L. occidentalis was observed in all main geographic areas of Trentino, up to the subalpine belt in the southern part of the region. The seed bug completed one or two generations depending on altitude and local climatic conditions. Field data and rearing under artificial conditions indicated the importance of heat accumulation for the development of nymphal instars and the role of temperature thresholds in regulating adult behaviour. The seed bug was observed on trees (Pinus nigra, P. sylvestris) as well as on shrubs (P. mugo), facilitating the rapid colonisation of a fragmented mountain environment. This may have important implication in the dispersal of pathogens, as spores of Diplodia pinea were detected on adults. Although a direct economic impact has not been evidenced yet in this alpine area, an ecological impact hampering natural regeneration, especially in high-altitude forest ecosystems, can be envisaged.