Invasiveness, seasonal dynamics, and impacts of Xylosandrus compactus on natural and cultivated vegetation in Israel, with notes on the implications of its management

The black twig borer (BTB) Xylosandrus compactus is a highly invasive ambrosia beetle that infests a wide range of living woody hosts. It was first detected in Israel in 2020, and since has caused substantial damage, particularly to ornamental trees in the Western Galilee. This study examined its distribution, host range, seasonal activity, reproductive success, and potential control measures. Field surveys conducted during 2022–2025 across Western and Upper Galilee documented infestation symptoms and confirmed reproduction through the presence of developmental stages within galleries. An observation plot including seven susceptible tree species was monitored from September 2023 to November 2025. Control strategies included canopy applications of Beauveria bassiana – based formulation and trunk injections of emamectin benzoate. Additionally, 21 commercial fungicides were evaluated in vitro against the beetle’s symbiotic fungi ( Ambrosiella xylebori, Thyridium lauri, and Fusarium solani suspected as such). Results indicate that BTB likely entered Israel from southern Lebanon around 2019 and spread ~30 km southward by 2023, followed by a marked population decline in 2024–2025. Infestation peaked during late summer and autumn, with minimal activity in winter. Among 22 recorded host species, approximately two-thirds were native Mediterranean shrubs and small trees. About 37% of the overall sampled twigs contained viable brood, whereas Cercis siliquastrum exhibited the highest infestation levels. Neither of the tested formulations demonstrated clear efficacy in managing BTB symptoms under field conditions at two locations. Only a few fungicides showed strong inhibitory effects on symbiotic fungi at low concentrations. The observed population decline could not be explained by host resistance, natural enemies, or abiotic factors. We propose that disruption of fungal symbionts by competing microorganisms may impair larval development, while dispersal of uncontaminated females may enable renewed outbreaks. These findings highlight the complexity of BTB population dynamics and the limited effectiveness of current control measures.