New evidence on the spread in Catalonia of the invasive longhorn beetle, Xylotrechus chinensis, and the efficacy of abamectin control

Abstract

The invasive wasp-mimicking Tiger Longicorn Beetle, Xylotrechus chinensis, a potentially lethal pest of mulberry trees (Moraceae: Morus), was first reported in Europe in 2018. In Catalonia its spread has been impressive: one district, four towns, 44 km2 in February 2018; four districts, 12 towns, 378 km2 in July 2020; seven districts, 65 towns, 1,134 km2 in December 2023. It is likely the infestation will spread further in the future, specially along the Mediterranean coast from Spain to Greece. The flight period of this beetle in Mediterranean countries is expanding on both ends (from the end of April to the end of October), probably due to increasing temperatures because of climate change. The adult beetle life span is 18-23 days in insectaria, likely somewhat shorter in the wild. The single treatment with abamectin carried out in a Catalonian town in June 2022 on a sample of 24 trees (12 treated, 12 untreated) has been effective in reducing the infestation of this beetle in relation to untreated trees. But the reduction was not complete since new emergence holes appeared during the summer of the following year. Therefore, a reinforcing treatment carried out during the first ten days of October is recommended to control this pest. Also, to get satisfactory mulberry trees protection, treatments should be repeated during a few consecutive years. Yearly re-infestations from untreated public and/or private mulberry trees are also a concern and make short-term control of this pest difficult, no doubt accounting for the rapid spread of this beetle.