The invasive longhorn beetle Xylotrechus chinensis, pest of mulberries, in Europe: Study on its local spread and efficacy of abamectin control.

The invasive wasp-mimicking Tiger Longicorn Beetle, Xylotrechus chinensis, a potentially lethal pest of mulberry trees (Moraceae: Morus sp.), was first reported in Europe in 2018, although its colonization and establishment were estimated to have occurred during the year 2012 or earlier. In Catalonia the infestation spread from four towns and 44.1 km2 in 2018 to 12 towns and 378.1 km2 in 2020; in the studied town of Barberà del Vallès, infested trees rose from 16.21% in February 2016 to 59.29% in December 2018. Human safety in public parks and avenues is a concern, as beetle infestation increases the risk of falling branches. The main objective of this study was to evaluate how the infestation progresses over time, with and without abamectin treatment, and provide insights into female egg-laying preferences. Such knowledge helps contribute to management efforts to reduce expansion of the range of beetle infestation. Our statistical analysis shows that females prefer laying eggs on larger trees, on the highest part of trunks and on the crown base (this being more preferred than the trunk), and they do so on warmer, SW orientations rather than those facing N, NW and E. Emergence holes and gallery slits predict the spreading of infestations to new trees. An abamectin treatment (trunk injection) carried out at the end of April significantly reduced the number of new infestation. However, for maximum insecticide efficiency, the best time for treating with abamectin would be from mid-July to mid-August, when newly hatched larvae begin feeding on the phloem.