Europe has been invaded by two insect species that North Americans should be watching out for. First, a Cerambycid, the wasp-mimicking tiger longicorn beetle, Xylotrechus chinensis. And second,the Buprestid cypress jewel beetle, Lamprodila festiva. We should also ensure that none of the other 500+ beetles introduced to Europe poses a threat to our trees. These are summarized in a 2024 paper by Bunescu et al.
Tiger Longicorn Beetle
This beetle is native to eastern Asia. It feeds on and kills mulberry trees (Moraceae: Morus spp.). It might also attack apple and pear trees and grapevines – Asian sources report these as hosts. The status of grapevines has been questioned by a Spanish experiment, in which artificial inoculations failed. I have seen no further information about the vulnerability of apple (Malus spp.) and pear (Pyrus spp.) (Saarto i Monteyu, Costa Ribeu, and Savin 2021)
In Europe, the pest threatens mulberry trees which are commonly planted for shade and ornamentation, especially in southern France, Spain and Greece (Saarto i Monteyu, Costa Ribeu, and Savin 2021). For example, there are more than 20,000 mulberry trees in Athens (EFSA 2021). The trees’ abundance contributes to spread of any associated pests, the level of damage caused by falling branches, and the expense of tree removal. Economic damages are those typically associated with wood-borer invasions of urban areas. That is, the cost of tree removals, loss of shade and amenity values, and increased risk of injury from falling branches.
We Americans should be concerned, too. Wild red mulberry (Morus rubra) occupies much of the eastern United States, from southern New England west to southeastern Minnesota, then south along the eastern edge of the Great Plains to central Texas, and east to southern Florida. It is also found in Bermuda. It grows primarily in flood plains and low moist hillsides. . Presumably it would also be attacked by Xylotrechus chinensis, although I don’t know whether anyone has tested this. As a native tree, red mulberry plays a role in natural ecosystems, including wildlife food supplies. Thus, America would see even more significant losses if Xylotrechus chinensis were to establish.
Red mulberry is already declining in parts of its central range, possibly due to a bacterial disease. The effects and extent of this disease have not been investigated thoroughly.
Apples and pears are important crops across North America; the farm-gate value is estimated at $3.2 billon.
Introductions of the beetle to Spain, France, and Greece might have resulted from inadequately-treated wood packaging or other wood products. Detections of the species in wood imports were reported in Germany in 2007 and 2017 (Saarto i Monteyu, Costa Ribeu, and Savin 2021). The U.S. has also intercepted X. chinensis at least once, at the port of Philadelphia, in 2011 (EFSA 2021).
These detections have raised questions to which no-one yet has answers. First, can X. chinensis develop in cut logs? The European Food Safety Agency concluded that it can (EFSA 2021). Second, one detection involved a shipment of wooden items made from birch (Betula spp.) and willow (Salix spp). It is not yet clear whether these taxa are also hosts (EFSA 2021). (The wood species were not specified in the case of the other interceptions.) I have blogged often about how “leaky” the wood packaging pathway has been; to see these blogs, scroll below the “archives” section of the webpage, then click on the category “wood packaging”.
European scientists believe X. chinensis might also be transported in shipments of plants for planting. However, the beetle prefers to oviposit on large trees. This pathway is less viable for the United States since USDA APHIS allows imports of mulberries (Morus) and pears (Pyrus) only from Canada. Apple trees (Malus spp.), however, may be imported from France – which hosts an introduced population of X. chinensis – and other European countries.
Detection of any invasion by X. chinensis will pose the usual difficulties associated with woodborers. In some European cities, hundreds or even a thousand trees were infested before the outbreak was detected (EFSA 2021).
I am concerned that the Europeans appear to have been slow to respond to the threat from Xylotrechus chinensis. After several outbreaks were discovered in Greece, France, and Spain in 2017 and 2018, the European and Mediterranean Plant Protection Organization (EPPO) added X. chinensis to its Alert List. This action requires member states (which are not limited to European Union members) to report new outbreaks and inform about efforts to either stop or eradicate them (Saarto i Monteyu, Costa Ribeu, and Savin 2021).
Shortly afterwards the European Union Commission requested the European Food Safety Agency (EFSA) to conduct a risk assessment. This analysis was completed in 2021. (It contains lots of photos of the insect and its damage.) The analysis concluded that Xylotrechus chinensis could probably infest most areas in the Union and cause significant damage. The species meets the criteria for designation as a quarantine pest in the Union. However, as of December 2024, this action had not been taken. As a result, control measures for this species are not mandatory.
Introductions continue; an outbreak in Lombardy, Italy, was found in June 2023 (Sarto i Monteys, Savin, Torras i Tutusaus & Bedós i Balsach 2024). European regulations – following IPPC standards – also are linked to named pests and known outbreak locations. Such restrictions almost guarantee that the pest will continue to spread from not-yet-detected outbreaks. (Decades ago, after the emerald ash borer invasion, Michigan’s State Plant Regulatory Official, Ken Rasher, noted that, to be effective, “slow the spread” efforts must apply to areas beyond the known limits of the pest’s range.) The EFSA risk assessment did suggest delimitation of buffer zones around known European outbreaks. I don’t know whether such zones have been set up.
The risk assessment also recommended [true?] improving detection of this insect by developing male pheromones as lures. These have not been acted on. Guidance on best timing for treatment [trunk injections of systemic insecticides] also appears to have been taken up by Greece but not by Spain (Sarto i Monteys, Savin, Torras i Tutusaus & Bedós i Balsach 2024).
These authors include more information about the Xylotrechus chinensis life cycle and trajectory of the invasion,. They note that climate change appears to be altering the insect’s phenology. Especially, the adult flight period is beginning earlier in the spring.
Cypress jewel beetle
This second pest of concern is a buprestid that attacks trees in the Cupressaceae. Infested trees generally die within a few years.
In its native Mediterranean range, the beetle feeds on native Juniperus, Cupressus and Tetraclinis. In invaded urban landscapes of Europe it attacks primarily introduced Cupressaceae , particularly Thuja, Chamaecyparis, Platycladus, Callitris, and some hybrids (Cupressocyparis). It has also been recorded as damaging Sequoia sempervirens (Brunescu, et al., 2024). (Genera in bold are native to North America.)
White cedar, Thuja occidentalis is the focus of Brunescu, et al.’s article. It is native to eastern Canada and much of the north-central and northeastern United States. The European and Mediterranean Plant Protection Organization (EPPO) has identified eight species in the Lamprodila genus as important pests, (Brunescu et al. 2024) so the danger might be more widespread. The invasion of Europe is probably the result of adult flight or other short-range transport. The article does not suggest pathways that the species might exploit to cross oceans.
SOURCES
Bunescu, H., T. Florian, D. Dragan, A. Mara, I-B. Hulujan, X-D. Rau. 2024 The Cypress Jewel Beetle Lamprodila Festiva Linné, 1767 (Coleoptera: Buprestidae), an Invasive Major Pest of Thuja Occidentalis Linné in Romania Hop and Medicinal Plants, 2024 XXXII, No. 1-2, 2024.
Saarto i Monteyu V., A. Costa Ribeu. I. Savin. 2021a. The invasive longhorn beetle Xylotrechus chinensis, pest of mulberries, in Euro: Study on its local spread & efficacy of abamectin control Plos One January 29, 2021. https://doi.org/10.1371/journal.pone.0245527
Sarto i Monteys, V., I. Savin, G. Torras i Tutusaus & M. Bedós i Balsach. 2024b. New evidence on the spread in Catalonia of the invasive longhorn beetle, Xylotrechus chinensis, & the efficacy of abamectin control. Scientific Reports | (2024) 14:26754 | https://doi.org/10.1038/s41598-024-78265-x www.nature.com/scientificreports/
Posted by Faith Campbell
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For a detailed discussion of the policies and practices that have allowed these pests to enter and spread – and that do not promote effective restoration strategies – review the Fading Forests report at https://treeimprovement.tennessee.edu/
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