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

The invasive wasp-mimicking Tiger Longicorn Beetle, Xylotrechus chinensis, a potentially lethal pest of mulberry trees (Moraceae: Morus spp.), was first reported in Europe in 2018. In Catalonia its spread has been impressive: one district, four towns, 44 km in February 2018; four districts, 12 towns, 378 km in July 2020; seven districts, 65 towns, 1134 km in December 2023. It is likely the infestation will spread further in the future, in particular 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 mid-October), probably due to increasing temperatures because of climate change, although this should be further proved. The adult beetle life span is 18-23 days in insectaria, likely somewhat shorter in the wild since they do not feed and spend more energy flying outside. 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 exit holes appeared during the summer of the following year. Therefore, an additional treatment carried out during the first ten days of October should be tested to achieve a better control of this pest. It would also be worthwhile trying a single treatment of abamectin in mid-July since it should be able to kill larvae hatching before the treatment and still have sufficient residual activity for larvae hatching after the treatment, and thus cover the entire activity period. Also, to get satisfactory mulberry tree protection, it is likely that treatments might have to be repeated for 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.