**1. Introduction**

The natural range of the box tree moth (*Cydalima perspectalis* Walker, 1859) is in Southeast Asia's humid subtropical regions. Described in the mid-nineteenth century from China, it was found in India half a century later. At the turn of the 20th and 21st centuries, its presence was confirmed in Korea, Japan, and Russia's the Far East [1–3]. *C. perspectalis* was recorded in Europe for the first time in 2007 in Germany (Baden-Württemberg, the city of Weil am Rhein) and in the Netherlands. Considering the size of the damage done at the place of its first finding should be assumed that it was brought to Europe at least two years earlier. The places of dispersion to Europe are most probably the distribution centers of ornamental plants imported from China in Germany and the Netherlands [1]. Eggs and caterpillars, especially of the earlier stages, move easily along with the boxwood bushes (including cuttings) transported for commercial purposes. Molecular studies of the mitochondrial cytochrome oxidase I and II genes indicate that the source of European populations is multiple introductions of insects from eastern China due to the rapid, longdistance transport of boxwood shrubs as part of the ornamental plant trade from this country to Europe. The lack of precise legal regulations in the trade of ornamental plants, the liberalization of the existing law, and the general trade globalization facilitated such a

**Citation:** Bere´s, P.K.; Zi ˛etara, P.; Nakonieczny, M.; Kontowski, Ł.; Grzbiela, M.; Augustyniak, M. *Cydalima perspectalis* in Poland—8 Years of Invasion against the Background of Three Other Invasive Species. *Diversity* **2022**, *14*, 22. https://doi.org/10.3390/d14010022

Academic Editor: Luc Legal

Received: 24 November 2021 Accepted: 23 December 2021 Published: 31 December 2021

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rapid spread of the species to and in Europe [4]. By 2020, *C. perspectalis* had infested almost all of Europe (Figure 1). It is recorded from Great Britain through southern Scandinavia, Lithuania, Western Ukraine, and Russia in the east, to the Balkans and Portugal in the south [4–13]. It has also been reported in Turkey, Georgia, and Dagestan [14–16]. The current range of occurrence of this species in Europe is consistent with the bioclimatic model (CLIMEX®) prepared in 2014 for *C. perspectalis*, in which its potential range was established based on the lower development threshold temperature, which depends on latitude and altitude (up to 2000 m above sea level in Georgia). The range of *C. perspectalis* in the north is limited by the low temperature, which prevents the closure of one life cycle per year. In the south, by the requirements related to obligatory diapause [5].

**Figure 1.** "Twist of fate"—a boxwood hedge in front of the European Museum in Schengen, damaged by an East Asian invasive box tree moth (September 2019). Photo: M. Nakonieczny.

The biology of the species in Poland has not been fully described yet. In Europe, *C. perspectalis* can develop up to five generations a year depending on the latitude. The main factor limiting its development is temperature, as the lower developmental threshold for the immature stages is 8–12 ◦C. However, it is known that it has a variable number of generations during the year, depending on weather (mean temperature) conditions too. The female lays gelatinous, transparent eggs with up to 20 in the batches. A maximum of a female can lay up to 500 eggs [3,17]. Depending on the temperature, 2–3 mm long larvae hatch from the eggs after a few to several days. Then, 3–4 weeks later, they reach their maturity size of about 4 cm. At a temperature of 20 ◦C, the development from hatching to the adult takes about 40 days [5,17]. At 25 ◦C, the average duration of each larval stage is three days, with an extended photoperiod shortening the development time of the larvae [18]. The pre-pupa stage lasts approximately eight days. At 25 ◦C, the imago appears after about ten days. The adult insect lives up to two weeks. In autumn, when the temperature drops, the caterpillars build cocoons from the leaves and hibernate [5,17,19]. In Central Europe, where there are usually two generations, the insect needs 518 degree days for the over wintering generation, and 430 for the second generation to complete the cycle. This difference translates into a different mean growth rate, higher in the first generation of insects feeding in spring than in larvae feeding in autumn [17].

Hatching larvae feed as a group first and then disperse. The foraging during the boxwood growing season varies spatially. In spring, most of the larvae feed in the lower parts of the shrubs. In summer, they feed on the middle parts, and in autumn, they feed on leaves in the top part, which causes of plant death [20]. Last instar larvae, in the leaves absence, may feed on the shoots by gnawing out phloem. Foraging is accompanied by the formation of filaments that form dense, hydrophobic clusters of leaves, which facilitates the identification of attacked plants, but makes it difficult to control the larvae, both by chemical and biological methods. The pupa is tied in a cocoon of leaves entwined with yarn, protecting it against low temperatures and pesticides [17,19]. In Central Europe, the insect undergoes obligatory diapause in winter, lasting at least eight weeks. The larva of the 3rd stage of the second generation of insects usually hibernates [5,18]. It forms leaf cocoons, usually inside the bush, making it difficult to assess the degree of plant infestation and making it easier to withstand frosts. Over wintering caterpillars can survive a temperature drop-down to −30 ◦C, which is not uncommon in north-eastern Poland. Shortening of the photoperiod and the growing food shortage caused by the intensive feeding of the larvae of both generations, exceeding the regenerative capacity of the host plant, may cause diapause as well [3,18].

Recently, Suppo and his team [21] introduced the first phenology model for the box tree moth based on a temperature and photoperiod to simulate the life cycle of this insect and the developmental rate for each life stage. Minimum temperature appeared the most critical parameter for the model, while diapause was negligible. The model shows that higher temperatures associated with global warming can significantly increase the number of pest generations during the year and may lead to the overlapping of successive generations and the over wintering of caterpillars at various instars [21]. Results obtained by Poitou et al. [22] confirmed the positive effect of increasing temperature on the rate and dynamics of diapause termination and lack of stimulatory effect of photoperiod. The recent models of *C. perspectalis* spreading in Catalonia showed the importance of its host plant presence, dispersal capacity, and climate suitability [23].

On the map of the range of the box tree moth in Europe from 2012, prepared by a team of researchers from CABI–Switzerland [24], Poland was noted as a country where this species does not appear yet. The first information (published in Polish) about *C. perspectalis* in Poland comes from the village of Michałkowa in the Sowie Mountains (southwestern Poland, Lower Silesia), where the insect was detected in 2012 [25]. The following data on the places where the pest appeared come from 2015. This year, Blaik et al. [25] detected *C. perspectalis* in Suchy Bór near Opole (Opole voivodeship) and in the downtown Kraków (Lesser Poland), which indicates that the pest infested the southern part of the country. Further confirmed information on the range of *C. perspectalis* in Poland comes from southeastern Poland (Subcarpathian voivodeship). In the years 2016–2017, insects' presence was detected in the following towns: Grabiny, Rzeszów, Umieszcz, and Zgłobie ´n [26]. This expansion clearly indicated the latitudinal direction of the insect spread in Poland, parallel to the Carpathian arc until the 2017 year.

An example of a quick and destructive boxwood moth invasion is the Botanical Garden in Łód´z (central Poland). The first signs of foraging were found in the autumn of 2018, while in June 2021, the last, utterly dead boxwood hedges were removed. The garden does not currently have any boxwood collection (Figure 2a–c).

An important document that authorized us to undertake monitoring activities is the "Proposal for a resolution of the European Parliament on the boxwood moth (*Cydalima perspectalis*)", which encourages the Commission to:


The recognition by the EU of the need to monitor the boxwood moth in Europe indicates that the importance of this species is very high and noticeable in individual countries where *C. perspectalis* can pose a severe threat to boxwood hedges and topiaries as well as wild plants.

**Figure 2.** About a 50-year-old boxwood hedge damaged by *C. perspectalis* in the Botanical Garden in Łód ´z (Central Poland): (**a**) traces of feeding found one year after the first box tree moth was noticed in the garden despite the use of an insecticide (Łód´z, October 2019); (**b**) wholly defoliated hedge in the Botanical Garden in Łód ´z in June 2021; (**c**) dead boxwood shoots without bark (June 2021). Photo (**a**–**c**): M. Nakonieczny.

In the last 30 years, the invasion of many insect species, alien to the Polish entomofauna, have been found in Poland [28]. However, some of them were particularly spectacular and of real economic importance. These include the invasions of *Ostrinia nubilalis* (European corn borer), *Diabrotica virgifera virgifera* (Western corn rootworm), and *Cameraria ohridella* (Horse-chestnut leaf miner). There are many differences and similarities to that found for *C. perspectalis* in their pace and spread directions.

The study aims were to determine the current range of *C. perspectalis* occurrence in Poland, and the pace and degree of its invasiveness. Obtained data will allow a more precise definition of the threats to the cultivated boxwood, especially those of historical and cultural importance. A comparison of the invasions of the box tree moth with other invasive species in Poland from the last 20 years should enable the use of models of spatial spreading and occurrence developed for other species. Although in 2020, *C. perspectalis* was recorded almost all over Poland, there are no officially published data on this subject.

### **2. Materials and Methods**

### *2.1. Cydalima Perspectalis*

In Poland, the official monitoring of pest's occurrence conducted by the Main Inspectorate of Plant Health and Seed Inspection does not cover *C. perspectalis*. In the European Union, it is not a quarantine organism. For this reason, since its first finding in several locations in the southwest and southern Poland in 2012 [25,26], there is no reliable and systematic information about the directions of the spread of this species. Because box trees are cultivated all over Poland, especially *Buxus sempervirens*, many scenarios for this insect's spread were possible.

Because there is no system for monitoring the spread of the box tree moth in Poland, in 2018–2020, it was decided to establish its range. Since 2018, there has been a dramatic increase in the number of reports from gardeners and plant breeders in southern and central Poland about damaged box trees as a result of foraging a new, unknown boxwood pest. However, the problem was that in the national database, which is responsible for tracking the spread of various species in Poland, operating as part of the Biodiversity Map conducted by The Polish Biodiversity Information Network (PolBIN, KSIB) in 2018, only one town was listed (Warsaw) to be infested by *C. perspectalis* [29].

To identify the current range of *C. perspectalis* occurrence in Poland, the database of the internet website "Allotment and Garden Our Passion" [30], which brings together over 15,000 gardeners from Poland, was used. For this purpose, hobby gardeners gathered around this website provided information via social media (Facebook, Instagram) about the towns where they found the box tree moth on their plants from April 2018 to November 2020. Using the e-mail address provided on the main page of the website using the subwebsite "Contact", they provided the name of the place in their e-mail correspondence, including additional information, e.g., the date of the pest's appearance, photographs, or information (photographs) about the condition of the boxwoods. Each year, these places were verified by analyzing the photos of the damage and/or insects sent and field trips. Inspection visits were carried out annually from April to September, especially to locations from which the submitted documentation raised any doubts (Figure 3a,b). The presence of the box tree moth was verified in all voivodeships (the highest-level administrative division of Poland) from which the reports came. Particular attention was paid to the places farthest from where the box tree moth had already been found in previous reports. The resulting maps of the range of the box tree moth do not cover all the places where *C. perspectalis* occurs but show critical areas for subsequent reports of this insect's presence.

**Figure 3.** *Buxus sempervirens* bushes damaged by *C. perspectalis*: (**a**) an example of a positively verified photograph uploaded to the website "Allotment and Garden Our Passion"; (**b**) an example of verification of a report on the presence of *C. perspectalis* in the field: Trzebownisko near Rzeszów, September 2020, Photo: P. Bere´s.

*2.2. Ostrinia nubilalis, Diabrotica virgifera virgifera, Cameraria ohridella (Selected Methodological Issues for Comparative Purposes)*

• *Ostrinia nubilalis*. In Poland, monitoring of this species was carried out by inspectors of the State Plant Health and Seed Inspection Service (SPHSIS) and the Institute of Plant Protection-National Research Institute, Regional Experimental Station in Rzeszów (IPP-NRI). The monitoring started in 2004, and was completed in 2013. As it would not be a quarantine pest, the observations made by inspectors were only used to signal the presence of the pest in the second-degree administrative division units in Poland (the first-degree are voivodships), such as counties and cities with the rights of counties (there are 380 counties in Poland). Therefore, 50 to 150 plants at the ripening dough stage (BBCH 85) were inspected depending on the cultivation area. On small maize crops on up to 1 ha, 50 plants were observed, while on fields of more than 1 ha, the number of plants increased to 150. Inspections were carried out at the end of August and the beginning of September. Observations were carried out based on the methodology provided in an annex to a manual for plant inspection services concerning forecasting, alerting, and data recording drawn up by SPHSIS. In all the years of the study, observations were terminated when any signs of caterpillars feeding were recorded. The county taken by *O. nubilalis* was considered any in which symptoms of caterpillars feed on at least one maize plantation. Hence, the monitoring was qualitative rather than quantitative [31,32].

