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

Abstract

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.

Pest categorisation of Xylotrechus chinensis

“…The presence of the pest in a tree can be detected visually by round emergence holes, 5–6 mm in diameter (Figure 4 ), by bark wounds oozing tree sap and larval frass (Figure 5 ), in places where the larval galleries are very close to the bark surface, and by longitudinal slits (Figure 6 ) where the bark cracked above older galleries (Sarto i Monteys et al, 2021 ). Heavily attacked trees eventually die.…”

“…Catalonia (Sarto i Monteys & Torras i Tutusaus 2018 ; EPPO, 2018a ): 378.1 km 2 in 2020 (Sarto i Monteys et al, 2021 );…”

“…They are widely planted as shade trees in southern areas of the EU, e.g. France (Valladares et al, 2019 ), Spain (Sarto i Monteys et al, 2021 ) and Greece where there are more than 20,000 mulberry trees in Athens (D. Avtzis, Forest Research Institute, Hellenic Agricultural Organization Demeter, Vassilika, Thessaloniki, personal communication in email of 26.6.2021). However, Morus spp.…”

“…X. chinensis has the potential to spread fast. Sarto i Monteys et al ( 2021 ) report that, in Catalonia, the infestation expanded from 44.1 km 2 in four towns in 2018 to 378.1 km 2 in 12 towns in 2020. In one locality (Barberà del Vallès) that was followed more closely, the proportion of infested trees rose from 16.21% in February 2016 to 59.29% in December 2018.…”

Efficacy of Two Neonicotinoid Insecticides against Invasive Wood Borer Aromia bungii Larvae in Dietary Toxicity Test

“…However, the efficacy of insecticide trunk injection (or soil drenching) against wood–boring pests has been reported by only a few field experiments [ 12 , 13 , 14 , 15 , 16 ]. Furthermore, detailed studies on the dose–response relationships between insecticides and wood–boring pests are scarce [ 17 , 18 ].…”