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

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Scientific Reports volume 14, Article number: 26754 (2024 ) Cite this article soluble granule

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 km2 in February 2018; four districts, 12 towns, 378 km2 in July 2020; seven districts, 65 towns, 1134 km2 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.

The invasive wasp-mimicking Tiger Longicorn Beetle, Xylotrechus chinensis (Chevrolat 1852) (Figs. 1, 2 and 3), native to the East Palaearctic region (NE China, Taiwan, Korean peninsula, and Japan), is a serious pest of mulberry trees (Moraceae: Morus spp.). It was first reported as settled in Europe in 2018, specifically in Catalonia (NE Spain)1,2, although the colonization and establishment of this beetle there might have occurred during the year 2012 or earlier. Soon afterwards it was reported as established in Greece, southern France and the region of València in Spain (see3 for comprehensive details of sites and literature). On June 10, 2023 it was found for the first time in Italy, at Prevalle, as well as at Muscoline (June 23) and Roè Volciano (July 2), all in the province of Brescia (Lombardy)4. Later, during July 2023, the Plant Health Service of Lombardy conducted visual inspections on mulberry trees in nine municipalities of this province: Salò, Roè Volciano, Gavardo, Prevalle, Muscoline, Puegnago sul Garda, San Felice del Benaco, Manerba del Garda and Calvagese della Riviera, observing signs of infestation in all of them excepting the last two. In total 36 Morus trees were found to be infested5.

Xylotrechus chinensis. (a) Adult male emerged from mulberry bolts (photo V. Sarto i Monteys). (b) Two females moving fast on a mulberry trunk (photo C. Inglada).

Xylotrechus chinensis. (a) Beetle leaving the tree and making an emergence hole (EH) after completing the metamorphosis. (b) Idem, closeup. (photos G. Torras).

Xylotrechus chinensis damage and egg laying. (a) Strongly affected mulberry tree, in a terminal state. (b) Egg laying on mulberry bark. (photos G. Torras)

X. chinensis reached Catalonia no later than 2012, since based on information provided by citizens keeping mulberry trees in their gardens, first sightings of the beetle took place in July 20131. Since then, it spread rapidly. By 2021 it was already found in 12 municipalities, starting from the initial 43. When the present work has been completed (December 2023), it was found already in 65 municipalities (see below for details). Safety in parks and public avenues has become a concern since the infestation of beetles increases the risk of falling branches on pedestrians. The European Food Safety Authority (EFSA) Panel on Plant Health performed a pest categorisation of X. chinensis for the EU territory and concluded that this beetle satisfies all the criteria that are within the remit of EFSA to be regarded as a potential Union quarantine pest6.

The main objective of this study was threefold. To check if the seasonality of this beetle is changing (likely due climate change), to see how the beetle spread in Catalonia during the last six years (2018–2023) and to evaluate if only one treatment with abamectin (trunk injection) carried out at the beginning of June 2022 was effective and sufficient to reduce the beetle population in the trees in the following year 2023. In addition, the June 2022 treatment should not affect the beetles emerging during the immediately following summer (July, August and September 2022), since in June 2022 beetles originating from eggs laid in summer 2021 were in the pupal stage, therefore neither feeding nor affected by the abamectin injected this month. The latter assumption had to be statistically tested though, and we did this as described below.

In previous studies, abamectin injected to mulberry trees has been notably effective at reducing X. chinensis infestation, although trunk injections should be carried out at least once a year for several consecutive years7,3. Three more insecticides have been tested against X. chinensis for long-term control of mulberry trees, these being fipronil, imidacloprid and spirotetramat, the first two giving good results (emergence holes reduced by 72–76% in 2 years)7. Drawbacks are that trunk injections are more expensive and time-consuming than other methods, and town halls and citizens with mulberry trees in their gardens may not be willing to use this method, even knowing their trees are infested. This inevitably will cause reinfestation and likely explains the rapid spread of this pest wherever it has established.

As to the seasonality, on May 10, 2020, the first author was called to supervise the cutting and recover all pieces of an old mulberry tree. It was heavily infested and located in a private garden within the town of Molins de Rei (Barcelona). The owner decided to cut it completely, using a chainsaw, to reduce infestation of other mulberry trees. All pieces were caged in semi-field conditions within a 1.20 × 1.50 × 2.10 m3 wire mesh cage, located in a nearby forest close to our lab. Then we checked daily adult emergences from May 11 to October 7, 2020. We also checked for early adult emergences at the town of Barberà del Vallès while we were counting emergence holes on May 2022 (before the expected emergence of new beetles in summer 2022).

As to the life span of X. chinensis adults, we collected 66 adults in July 2017 from the semi-field cage mentioned above. Collection took place the same day the beetles emerged from the bolts where they had overwintered (see1 for details). At emergence, their sex and emergence date were also recorded. These specimens were placed into three insectaria (50 × 25 × 32 cm3) together with vine trunks and mulberry trunks as mentioned in1. The temperature in the room was 26 ºC and insectaria were water-sprayed every second day to provide some humidity (adult beetles do not feed). There, they were left to evolve until they died. Dead beetles were removed from the insectaria daily, and the date of death was recorded.

As to the spread of this beetle in Catalonia, data were gathered directly by visiting many towns up to December 31, 2023. Many anonymous private citizens also provided valuable data; in all cases they were asked to send photographs. Data from municipalities within the province of Tarragona (south Catalonia) were mostly given by staff working at the Plant Health Service (Government of Catalonia). In addition to that we also got data from City Council Technicians and Phytosanitary Treatment Companies. All data received from outside sources were carefully checked to ensure they were indeed referring to X. chinensis. We also recorded the year when these records were first communicated to us, although in all cases it is likely the beetle reached a place at least two years earlier.

All methods were carried out in accordance with relevant guidelines and regulations. All experimental protocols were approved by the Plant Health Service (Government of Catalonia). Informed consent was obtained from all subjects mentioned in this work.

Finally, we evaluated if only one treatment with abamectin (trunk injection) carried out at the beginning of June (June 7, 2022) in the town of Barberà del Vallès (Barcelona) was effective and sufficient to reduce the beetle population in the trees in the following year (2023). For that, we selected 24 mulberry trees, and on May 23, 2022, we counted the number of emergence holes (EH) present on their trunk and crown base, marking them lilac. Obviously, these EH counted in May 2022 have been made by beetles emerged during the previous summer (2021). After that we arranged these trees into four groups of six, according to their number of EH (Table 1). Subsequently, we randomly selected 12 out of 24 trees to treat them with abamectin in June 2022.

SI1 Table describes the 24 trees studied, those that were treated (and not) with abamectin and the results of the emergence hole counts made on three different dates (see Table 2 for means and standard deviations). Each tree has a numerical code and for each one the perimeter of the trunk (at 130 cm from the ground) and its trunk height (from the ground to the crown base) were measured. The counts were made on the bark of the trunk (over four height bands) and crown base. In Table 2 and in SI1 Table, EH-trunk 25 collects the number of emergence holes counted on the bark of the trunk in the band that goes from the ground to a height of the trunk equal to 25% of the total height of this trunk. Thus, EH-trunk 50, EH-trunk 75 and EH-trunk 100 would be the same for trunk bands ranging from 26 to 50%, from 51 to 75% and from 76 to 100% respectively, of the total height of this trunk. EH-crown base collects the number of emergence holes counted on the bark of the crown base of the tree. Figure 5c shows the five zones mentioned above where the emergence hole counts were made on the trees.

To inspect that the two samples (treatment and control groups) are similar, and the treatment has been actually applied randomly, we can compare the descriptive statistics of these groups as of May 2022. One can notice that the sample treated with abamectin has lower number of emergence holes in the crown, while other characteristics look rather similar. To ensure that the two samples are comparable and to minimize the risk that our further conclusions are affected by this difference between the samples, we employed propensity score matching in line with3. In particular, we used the nearest neighbour matching algorithm in R MatchIt library version 3.0.28. Namely, we used variables on total EH and specifically EH on the crown of the tree as well as perimeter and height of the tree to match every tree treated with abamectin with a non-treated tree. As a result of this, the sample reduced from 24 to 18 trees which form a good match and exhibit comparable values on the four variables mentioned (see SI1 Fig.).

To test the role of abamectin treatment on new emergence holes, we carried out statistical analysis of new infestation in August 2022 as a function of past infestation (May 2022), height and perimeter of the tree, as well as the effect of the abamectin treatment. For that, since our dependent variable is a count one with many zeros and conditional means have a value much below their variances, we cannot use ordinary least squares (OLS) as the estimation method and instead use a negative binomial regression model (NBRM). NBRM is considered as a generalization of the Poisson regression as it has the same mean structure but also an extra parameter to model the over-dispersion. We run likelihood ratio tests that suggest that NBRM is a better option (than Poisson model) for our data. This approach is in line with3 who analysed similar data. Also, similar to3, we test as control variables square terms of perimeter and height of the tree to see if the relationship between new emergence holes and these characteristics is nonlinear. Thus, we empirically estimate the regression equation of the form:

where \(E{H_{t - 1}}~\) refers to the number of emergence holes either in May 2022 or August 2022 and \(E{H_t}~\) is the number of those holes either in August 2022 or August 2023, respectively, and \(Abamectin\) is a binary variable indicating if the tree was treated. The regression Eq. (1) follows the “residualized change approach”, where the new value is a dependent variable and the previous value is a control9,10.

EH counts and abamectin treatment:

The first EH count was done on May 23, 2022, before the treatment with abamectin. EH found were counted and marked lilac; these correspond to those already existing before the appearance of new beetles in the summer of 2022 (Fig. 5a).

On June 7, 2022, half of these 24 trees were treated with abamectin as indicated in SI1 Table. The treatment methodology was similar to that described in3. In sum, the dose of insecticide per drilled hole (trunk injection point) and drillings per tree are both determined according to the trunk perimeter. 10 ml of a mix containing 5 ml of abamectin 1.8% [EC] w/v (Vertimec®, register # 16784, Syngenta España, Madrid, Spain) and 5 ml of abamectin emulsifier (Endotree Mixable®, Endoteràpia Vegetal, Castelló d’Empúries, Girona, Spain) are injected to the tree per drilling. Typically, there are 2–3 drillings per tree, determined at the rate of one every 30 cm of trunk perimeter at a height of 130 cm. They are performed at the base of the tree trunk, between ground level and the first 20–25 cm, with a 7 mm drill bit, and evenly distributed around the perimetral circumference (Fig. 4).

The second EH count was done on August 16, 2022. New holes found after the emergence of new beetles in the summer of 2022 were marked orange (to differentiate them from those marked lilac during the May 23, 2022 count) (Fig. 5b).

The third (and last) EH count was done a year later, on August 17, 2023. The new holes found were marked white and were made by beetles that emerged during the summer of 2023. Tree # 57, from group IV, fell over and had to be cut down. It could not be included in the statistical study.

Treatment with abamectin (June 7, 2022). (a) Mulberry trees to be treated were previously numbered. (b) Endotherapy treatment to a tree. (photos G. Torras)

Emergence holes marked on mulberry trees. (a) EH marked lilac on May 23, 2022. (b) New EH marked orange on August 16, 2022. (c) Five zones selected for counting EH on the trees. Also shown are the three colours used to mark the holes during this trial, i.e. lilac, orange and white (see text); in this figure only the orange ones are real. (photos G. Torras).

With respect to the above, we do not expect the June 7, 2022 treatment to affect beetle emergence for the summer of 2022 (the beetles should be in the pupal stage and do not feed when they leave the tree, so they are not exposed to abamectin). In fact, the June treatment only targets young larvae hatching from eggs laid by this summer 2022 generation of beetles. So, to properly test the effectiveness of abamectin against this pest, we need counts from next summer 2023, and this was done on August 17, 2023.

In summary, we check if the treatment with abamectin carried out on June 7, 2022, (a) significantly reduced the number of EH appeared between May 23, 2022 and August 16, 2022 (Hypothesis 1: we expect it did not), and (b) significantly reduced the number of EH appeared between August 16, 2022 and August 17, 2023 (Hypothesis 2: we expect it did).

A total of 57 adults emerged from the portions of trunk obtained and caged from a heavily infested sole mulberry tree completely cut in pieces in May 2020 as explained above. The first adult emerged on May 16, the last in August 15. 20 adults out of the 57 emerged from May 16 to May 31. Also, at the town of Barberà del Vallès, while we were counting emergence holes on May 23, 2022 (in order to treat those trees with abamectin on June 7, 2022, as described above), we observed one recently emerged adult on those trees. And in the nearby town of Ripollet, two females were seen and photographed on a mulberry trunk (Fig. 1b) on May 26, 2024 (Mario Jiménez, Ripollet Town Hall, pers. com.). The latter observations seem to support the fact that the beetle is advancing its seasonality towards the spring (mid-May) at least in Catalonia. This is in considerable contrast with Japan, where adults emerge from July to August, and in Catalonia, so far, our earliest record was June 15th.

Another trait is the life span of X. chinensis adults, which has not yet been reported. By reviewing our data obtained from the insectaria and conditions mentioned above, we conclude that these adults lived between 18 and 23 days (gender was not checked). Further studies should be carried out to better precise the life span of males and females in the wild and environmental temperatures.

By December 2023, X. chinensis was found infesting mulberries in 65 towns and seven districts, covering 1134 km2 (Fig. 6). During the fourth quarter of 2023 we checked 16 additional towns close to the infested ones, with negative results (light green coloured in Fig. 6d below). SI2 table shows the districts, their infested towns and their areas, the degree of pest impact, the information sources and the first year of detection for each town.

Spread of Xylotrechus chinensis in Catalonia (NE Spain). (a) Catalonia within the Iberian Peninsula. (b) Municipalities infested (red) in 2018. (c) idem in 2020. (d) idem in 2023; light green colour shows municipalities visited by us, as to December 2023, which were not found infested yet. The municipal map of Catalonia was obtained from Institut d’Estadística de Catalunya (https://www.idescat.cat/). Map colouring was done with Datawrapper (https://app.datawrapper.de/).

Table 3 summarizes the results of estimating Eq. (1) above with NBRM. Shaded columns present models tested on subsample created with propensity score matching. As we can see from models 1–4 reported in this table, abamectin treatment is not significantly related to emergence holes counted in August 2022, which confirms our Hypothesis 1 above. In other words, the treatment with abamectin carried out on June 7, 2022 has no significant impact on new EH appeared between May/2022 and August/2022. Among other controls, we find some weakly significant nonlinear relation with height and perimeter: while very short or very tall trees or trees with very small/large perimeter exhibit lower number of new EH, the largest amount of infestation falls on medium sized trees.

We find a statistically significant and negative effect of abamectin treatment on new EH counted in August 2023 (compared to those counted in August 2022). If we take the overall EH count, the coefficient is significant at the 5% level. A regression coefficient of approximately − 1.1 in NBRM can be interpreted as that the abamectin treatment carried out leads to exp(1.1) = 3 EH less per tree on average (see models 5 and 6 in Table 3). Models 7 and 8 with propensity score matching (where the two samples are even more comparable) show consistent results, which further supports our Hypothesis 2.

Also, we used the same regression with the minimum set of controls (i.e., without squared terms as they were not significant for EH in August 2023) for different parts of the tree (see Table 4). Abamectin is not found to be significant for the 0–25%, 26–50% and 51–75% trunk height sections but weakly significant for 75–100% and strongly significant for the area of the crown base (p-value close to 0.01) and a coefficient close to 1.5 (i.e., the effect is exp(1.5) = approximately 4.5 EH less per tree if it has been treated with abamectin). Biologically speaking this makes sense, as females prefer to lay eggs at the top of tree trunks and at the base of the canopy3, so differences in EH (due to abamectin treatment) are expected to be more clearly detected in these areas of the trees.

In Asia, X. chinensis is univoltine, with adults emerging from July to August11. In Catalonia (Spain), it was reported1 that in 2016, the first adult emergence occurred on July 1st after ten consecutive days with an average daily temperature above 20 °C. However, in 2017, the first adult emergence was on June 15th and occurred after seven consecutive days of these same temperature values. It was also reported that in 2016 two females emerged extemporaneously on September 5th and 24th. And, again, in 2017, one male emerged on August 31st. The latter was considered exceptional by then.

Interestingly, Kavallieratos et al.12, based on a study carried out in 2021 and 2022 in three sites within Athens (Greece), using multi-funnel traps baited with different attractants, which collected a total of 1,645 adults (collecting started in mid-July 2021 and finished in mid-December 2022), reported that the flight activity of X. chinensis started at the end of April and finished at mid-October (last captures between October 18 and 21), with population peaks between mid-June and mid-August in 2022. Therefore, considering that, the ‘extemporary’ late emergences of 2016 and 2017 reported in Catalonia should not be considered exceptional, as much as those recorded in mid-May in 2020, 2022 and 2024 mentioned above.

In sum, we noticed the flight period of this beetle is expanding on both ends in Catalonia and based on our local climatic data (see1) we believe this is likely driven by the increasing temperatures because of climate change. Indeed, Catalonia, in general terms, has experienced an increase in average temperature in the last two decades. Figure 7 shows the evolution of the annual average temperature at the Fabra Meteorological Observatory, in the city of Barcelona, the closest (15 km) to our experimental field station. It has a century-old climate series. Values are shown as annual anomaly with respect to the average of the reference period 1961–1990, which is recommended by the World Meteorological Organization to capture long-term changes.

(Source: Meteorological Service of Catalonia, meteo.cat; https://www.meteo.cat/wpweb/climatologia/evolucio-observada-del-clima/evolucio-observada-de-la-temperatura/; accessed 22 July 2024) .

Evolution of the annual average temperature at the Fabra Meteorological Observatory, in the city of Barcelona (1915 to 2023).

In Greece, Kavallieratos et al.12 reported a seasonality for X. chinensis from the end of April to mid-October, though this was only complete for 2022. Therefore, unlike in Catalonia, it is not yet possible to draw conclusions about the possible effect of climate change in this Eastern European area.

Consequently, insecticide treatments against the larvae of this pest might have to be adjusted to its expanding seasonality, for instance treating in late spring and again in early fall. Yet, 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. Specific pheromone traps set locally should help determining the presence of adults in infested areas.

On other biological traits, Kavallieratos et al.7 mention that, after emergence, adults move towards the top of the tree to feed with the stems and leaves, and finally become sexually mature. And that, after hatching, larvae create galleries under the bark, gradually emphasizing the lower parts of the trunk and roots. According to our field data (see1), X. chinensis adults do not feed at all and are sexually mature as soon as they emerge from the tree. Also, we reported that in Catalonia females prefer laying eggs on the upper part of tree trunks and crown, so most larvae are found in these areas and less farther down; we found galleries in roots are very rare3.

As to the life span of X. chinensis adults, we concluded that adults lived between 18 and 23 days. However, keeping in mind that (1) the adults do not feed and fully rely on the food sources obtained by their larvae, (2) they moved actively around within the insectaria and often mated, but could not fly in there (if they did, they would crash into the insectarium walls), but they do fly in the wild, consequently spending more energy, then it is likely their life span is somewhat shorter in the wild.

Infestation spread in Catalonia and Europe.

The spread of X. chinensis in Catalonia since it was first reported in 2018 has been impressive. Indeed, by February 2018, Sarto i Monteys and Torras1 had found it in one district and four towns, covering 44 km2. Its expanse had grown to four districts and 12 towns by July 2020, i.e., 378 km23. And by December 2023, we reported its presence already in 65 towns and seven districts, covering 1134 km2.

In Europe, it is likely that the infestation will spread further in the future, in particular along the Mediterranean coast from Spain to Greece. Indeed, already known from Spain (Catalonia and València), Greece and southern France3, it was discovered in June-July 2023, and for the first time, in seven municipalities within the Italian province of Brescia (Lombardy)5,4.

Treatment with abamectin. Significance of abamectin treatment between (a) May 23, 2022 and August 16, 2022, and (b) August 16, 2022 and August 17, 2023 (based on EH counts).

In conclusion, the treatment with abamectin carried out in Barberà del Vallès on June 7, 2022 on a sample of 24 trees (12 treated and 12 untreated) has been effective in reducing the infestation of this beetle in relation to untreated trees, although the reduction was far from complete.

Also, as expected, the June 2022 treatment did not affect beetle emergences during the summer 2022 but did affect young larvae hatched from eggs laid by these summer beetles. These larvae (effectively reduced by abamectin) are the ones that would produce a new generation of beetles that would emerge in summer 2023. Fortunately, the June 2022 abamectin treatment largely prevented this, especially in the upper part of the trunks and crown bases, where the results are strongly significant (p-value less than 0.05) and a coefficient close to 1.5 (i.e., the effect is approximately 4.5 EH less per treated tree).

In sum, a single treatment with abamectin (done during the first ten days of June of a year) is far from 100% effective, since it does not manage to kill all the larvae hatched during the summer following the treatment and, consequently, new emergence holes appear during the summer of the following year. Therefore, an additional treatment carried out during the first 10 days of October should be tested to achieve a better control of this pest. However, given the rather expensive cost of the endotherapy treatment (about 50€/tree), it would also be worthwhile trying a single treatment of abamectin in mid-July to compare with the other treatment options. A mid-July treatment 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. The above had already been mentioned by us3 when we concluded the best time for treating with abamectin would be from mid-July to mid-August. Also, to get satisfactory mulberry tree protection, it is likely that treatments might have to be repeated during a few consecutive years. In Greece, trunk injection with abamectin during two consecutive years (carried out in July-August 2020 and again in July-August 2021) helped reducing beetle emergence holes in comparison with those counted in 2020 by 79.6% in 2021 and 85.6% in 2022; a similar trend was reported using three other insecticides12. 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.

Kavallieratos et al.7 reported the results of a trunk injection method with different insecticides to try managing this beetle in Athens (Greece). Unlike us, the trials lasted two consecutive years, and the insecticides tested were abamectin, fipronil, imidacloprid and spirotetramat, which were injected separately to four groups of 10 trees. A fifth 10-trees group was added as untreated control. All 50 trees were initially heavily infested by X. chinensis. Trunk injections were carried out between 15 July and 10 August 2020 and again between the same dates in 2021. They report that, after these two years of application, the percentage of emergence holes was reduced by 76.1, 71.8, and 85.6% in trees treated with imidacloprid, fipronil, and abamectin, respectively, while spirotetramat caused a 37.4% reduction, therefore concluding the first three could be used against X. chinensis for long-term control of mulberry trees. The statistical methods Kavallieratos et al.7 used are somewhat different from ours (e.g. they do not control specifically for abamectin but for all insecticides together in their regression analysis) making comparison of our results difficult. However, by counting the reduction of emergence holes for trees treated with abamectin in our sample between August 2022 and August 2023, we find the count reduced by 25%. The mulberry trees we studied, though, were much less infested than those of Greece, which likely accounts for the smaller percentage reduction in our case.

In Catalonia this invasive beetle is spreading rapidly. It did it from only one district, and four towns (44 km2) in February 2018 to seven districts and 65 towns (1134 km2) in December 2023. Already present south of Catalonia, in the Spanish València area, SE France, Italy and Greece, it is likely the infestation will spread further in the future, in particular along the Mediterranean coast from Spain to Greece.

We noticed the flight period of this beetle in Catalonia is expanding on both ends, which appears to be driven by the 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 by us (on June 7, 2022) has not been very effective in reducing the infestation of this beetle in relation to untreated trees. Indeed, the reduction was not complete since new emergence 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 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.

The datasets generated and/or analysed during the current study are available as online appendices (Supplementary information) or from the corresponding author on reasonable request.

Sarto i Monteys, V. & Torras, G. A new alien invasive longhorn beetle, Xylotrechus chinensis (Cerambycidae), is infesting mulberries in Catalonia (Spain). Insects 9(2), 52. https://doi.org/10.3390/insects9020052 (2018).