SEEFOR 16(1): 15-25
Article ID: 2508
DOI: https://doi.org/10.15177/seefor.25-08
ORIGINAL SCIENTIFIC PAPER
Leaf Mine Types and Associated Parasitism in the Invasive Tree Insect Pest Macrosaccus robiniella (Lepidoptera: Gracillariidae): a Case Study from Slovenia and Croatia
Natalia I. Kirichenko1,2,3*, Stanislav Gomboc4, Oksana V. Kosheleva5, Dinka Matošević6, Barbara Piškur3, Maarten de Groot3*
(1)Sukachev Institute of Forest, Siberian Branch of the Russian Academy of Sciences, Federal Research Center "Krasnoyarsk Science Center SB RAS", Department of Forest Zoology, Akademgorodok 50/28, RU-660036 Krasnoyarsk, Russia;
(2) All-Russian Plant Quarantine Center (VNIIKR), Krasnoyarsk branch, st. Zhelyabova, 6/6, RU-660020 Krasnoyarsk, Russia;
(3) Slovenian Forestry Institute, Department of Forest Protection, Večna pot 2, SI-1000 Ljubljana, Slovenia;
(4) Gančani 110, SI-9231 Beltinci, Slovenia;
(5) All-Russian Institute of Plant Protection (FSBSI VIZR), Laboratory of Phytosanitary Diagnostics and Forecasts, Podbelskogo 3, RU-196608 Saint Petersburg, Russia;
(6) Croatian Forest Research Institute, Division for Forest Protection and Game Management, Cvjetno naselje 41, HR-10450 Jastrebarsko, Croatia
Citation: Kirichenko NI, Gomboc S, Kosheleva OV, Matošević D, Piškur B, de Groot M, 2025. Leaf Mine Types and Associated Parasitism in the Invasive Tree Insect Pest Macrosaccus robiniella (Lepidoptera: Gracillariidae): a Case Study from Slovenia and Croatia. South-east Eur for 16(1): 15-25. https://doi.org/10.15177/seefor.25-08.
Received: 3 Feb 2025; Revised: 17 Apr 2025, 29 May 2025; Accepted: 2 Jun 2025; Published online: 24 Jun 2025
Cited by: Google Scholar
Abstract
Since its first documentation on the European continent in 1983, the invasive micromoth Macrosaccus robiniella (Clemens, 1859) (Lepidoptera: Gracillariidae) was known only for its lower-side blotch mines occupying one of the leaflet halves (common mine type, hereafter mine type 1). In 2023, in abundant populations of M. robiniella in forest areas of Slovenia and Croatia (with more than 50% of leaves damaged), we observed that, in addition to the common mine, this invasive species is capable of forming three other mine types. One (type 2) resembles the common mine type by occupying one half of a leaflet, but the mine is situated on the upper side of the leaf. The two other mine types differ from the common mine in both appearance and position on the leaflet. These include a blotch above the midrib on the upper side of the leaflet (type 3) and a narrow blotch at the edge, causing strong downward folding (type 4). The mines of types 3 and 4 resemble the damage caused by two North American black locust herbivores that are also invasive to Europe: the gracillariid Parectopa robiniella Clemens, 1863 (Lepidoptera: Gracillariidae) and the gall midge Obolodiplosis robiniae (Haldeman, 1847) (Diptera: Cecidomyiidae), respectively. In the studied localities, the relative abundance of mine types 3 and 4 was about four times higher than that of mine type 1. The parasitism rate in these mines was 6.5 times lower compared to that in mine type 1. No statistical difference was found in the parasitism rate between mine types 3 and 4. We discuss how the leaf-mining behaviour of M. robiniella may provide an enemy-free space, conferring a survival advantage and supporting a high population density in forested areas.
Keywords: locust leaf-miner; biological invasion; leaf-mining behaviour; parasitoid attacks; Europe
INTRODUCTION
Behavioural adaptations are crucial for invasive species (Gulzar et al. 2024). To become a successful invader, a species must show behavioural plasticity to be able to effectively compete for space and food resources in invaded regions (Catford et al. 2018). Additionally, it must evade native enemies and/or exploit enemy-free space to thrive in the new habitat and continue expanding its range (Jeffries and Lawton 1984, Torchin et al. 2003, Xirocostas et al. 2023).
The North American Macrosaccus robiniella (Lepidoptera: Gracillariidae) is a leaf-mining moth trophically associated with North American black locust, Robinia pseudoacacia L. This tree was introduced to the European continent in the 17th century, and since that time it has widely spread in European countries, penetrating forested areas (Vítková et al. 2017). Outside its native range, M. robiniella was first documented in 1983 in Switzerland (Whitebread 1990). In the following decades, the leaf-miner spread across most of the European continent (Davis and De Prins 2011), including the European part of Russia (Baryshnikova 2019). In Slovenia, M. robiniella was detected in 1994 (Seljak 1995, Maček 1999), and in Croatia in 2001 (Mešić and Maceljski 2001). Alongside M. robiniella, black locust has been the host to another invasive leaf-mining moth, the North American Parectopa robiniella (Lepidoptera: Gracillariidae), which was first observed in 1983 in Slovenia and 2001 in Croatia (Maceljski and Igrc 1983, Maček 1984). These leaf-mining moth species are now distributed across both countries (Matošević 2007, Gomboc and Kirichenko 2022).
In their invaded range, M. robiniella and P. robiniella share the same localities, host trees and in some cases even the same leaflets (Fodor and Hâruţa 2009, Medzihorský et al. 2024). Until recently, M. robiniella was known for its lower side tentiform blotch mines (common mine type) occupying one of the leaflet halves, whereas P. robiniella always forms its mines over the midrib on the upper side of the leaflet. Thus, both species effectively shared the same trophic niche by occupying a certain side of the leaflet (Fodor and Hâruţa 2009).
In 2019, in Slovenia in the forested area around the Ljubljana Castle (Ljubljana) and in Panovec forest (Nova Gorica), we observed that M. robiniella, in addition to its common mine type, was able to produce mines on the upper side of leaflets, occupying one of the leaflet halves (unpublished data). To our knowledge, in Europe, a single case of upper side mine was mentioned in Switzerland (Whitebread 1990). Opportunistic surveys conducted in 2023 revealed two other mine types with unusual positions on leaflets. Some mines were situated on the upper side above the midrib, similar to the mines of P. robiniella, whereas other mines were positioned at the leaf edge, causing strong downward folding, resembling damage caused by another North American insect, Obolodiplosis robiniae (Diptera: Cecidomyiidae). This was first recorded in Europe in 2003 in Italy (Duso and Skuhravá 2004) and is also present in both Slovenia and Croatia (Duso et al. 2005, Pernek and Matošević 2009).
We investigated the presence of different mine types of M. robiniella in forested areas in Slovenia and Croatia, where the moth exhibited notable abundance during the study year (2023). Specifically, we (1) described for the first time the mine types occurring in Europe, (2) estimated the abundance of different mines in dense populations of M. robiniella; (3) clarified whether there is a correlation with the co-occurrence with P. robiniella; and (4) determined whether parasitism rates differ among the different leaf mine types. We hypothesized that by producing uncommon leaf mines, the invasive leaf-miner may avoid native enemies (in particular, parasitoids) and, thus, have high survival and keep high population density in forested areas.
MATERIALS AND METHODS
Study Area
The study was carried out in Slovenia and Croatia (Figure 1). In Slovenia, the forested area around the Slovenian Forestry Institute in Ljubljana (46°3'6"N, 14°29'1"E, 305 m alt.) was explored.
In Croatia, sampling was conducted in a forested area in Krapinsko-zagorska županija (Krapina-Zagorje County), at two locations near the town of Pregrada: Kunagora (46°9'44"N; 15°44'43"E; 279 m alt.) (Figure 2) and Vinagora (46°10'25"N; 15°42'17"E; 262 m alt.).
Ljubljana is characterized by a continental climate with cold winters, humid springs and autumns, and warm summers. The average annual precipitation is about 1,400 mm, with the majority occurring between June and October (Slovenian Environment Agency 2025). The hottest months are July and August (on average around 21°C), while the coldest month is January (on average around 0°C).
Krapina-Zagorje County has a similar climate type but is slightly warmer with a moderately rainy climate. The temperature in July and August is about 22°C, while in winter the temperature can drop to –3°C (Izvješće 2018). Precipitation is also fairly evenly distributed throughout the year, with winter being the driest season. In Pregrada, annual precipitation ranges from 900 to 1,100 mm (Klima Hrvatske 2000).
Field Sampling
The fieldwork was conducted between October 1 and 14, 2023, during the period when mature mines from the second, most numerous generation of the moth, were present on the leaves. In the studied localities in Slovenia and Croatia, the populations of M. robiniella were noticeably abundant (with >50% of the leaves damaged and a proportion of 0.05 to 0.59 of the leaf compounds per attacked leaf (Table 1), which can also be referred to as a heavy infestation level. We surveyed R. pseudoacacia trees growing in open areas, i.e., at forest edges (Figure 2a). A total of thirteen trees aged 3–5 years were examined: eight in Croatia and five in Slovenia. The trees were chosen randomly. On each tree, four branches in the lower part of the tree were examined. All leaves on the branches were counted, and five leaves per branch were haphazardly detached and packed into zip-lock plastic bags for transport to the Department of Forest Protection of the Slovenian Forestry Institute (Ljubljana) for subsequent analysis. In total, 260 compound leaves and approximately 4,050 leaflets were examined across all localities (Figure 2a–d, Table 1). Data from the two countries were pooled, as the moth populations had similar densities (infestation level: >50% of all mined leaves on the sampled trees (Table 1)).
On each leaf, the number of leaflets was counted, and both the upper and lower sides were inspected for the presence and type of M. robiniella mines (Figure 3). Four mine types were identified (see Results). When several mine types were found on a single leaf, they were counted according to type, and the occurrence of different mine types on a single leaflet was also recorded. Furthermore, the number of P. robiniella mines and their combinations with M. robiniella mines were also recorded on individual leaves and leaflets.
Parasitism Documentation
Parasitism was estimated for all mine types, except for upper-side blotch mines situated on one of the leaflet halves, as such mines were rarely observed. Up to 35 mines of the three most common types were randomly selected from the examined leaflets for parasitoid rearing (mine type 1: 34 leaflets; mine type 2: 15 leaflets; mine type 3: 24 leaflets). Only leaflets with a single mine type were used. When multiple mines were present, the target mine, along with a surrounding green area (5–10 mm around the mine), was excised from the leaflet. Leaflets with mines or the excised mines were individually placed in plastic Petri dishes (60 mm in diameter) to allow parasitoid adults to emerge. The dishes with the mines were kept indoors in stable conditions (23°C, 50% humidity) for one month. At the end of this period, the dishes were inspected, and the emerged parasitoids and moths were counted. Parasitoid adults were preserved in 96% ethanol, and moths were pinned for collections. Mines from which nothing emerged were dissected under an Olympus SZ51 stereomicroscope (Tokyo, Japan, Olympus Corporation). In these mines, the number of parasitoid pupae and dead M. robiniella larvae or pupae (without signs of parasitism) was counted. When the cause of larval and pupal death was not identified, these individuals were all categorized as “died from unknown causes”.
Data Analysis
We used a contingency table with a Chi-square test to compare differences between the number of mine types with competition compared to the total number of mines, and parasitism (parasitoid emerged, adult moth emerged and unknown cause of death). A Chi-square test was also used to analyze the distribution of mine types with and without competition from P. robiniella, compared to a random distribution of mine types. Furthermore, the relative abundance was calculated per average leaf by dividing the number of mines by the number of leaflets and multiplying by 16 (the average number of leaflets per leaf). Differences in relative abundance and mine types were analyzed using a general linear mixed model (GLMM) with a zero-inflated negative binomial error distribution using the “glmmTMB” library (Brooks et al. 2017). Location, tree ID and branch ID were nested and included as random effects. A post hoc Tukey test was conducted using the “emmeans” library (Lenth 2023). The analyses were performed in the R (R Core Team 2022) and PAST (Hammer et al. 2001) statistical programs.
A map showing the current distribution of M. robiniella in Europe was created based on the data from Baryshnikova (2019) and De Prins and De Prins (2024), with an update from iNaturalist (2025). Countries where the moth was recorded are indicated in their entirety, except for Sweden, where only the southern part is shaded.
RESULTS
Description of Mine Types
Four mine types were observed in M. robiniella in the studied forested areas in Slovenia and Croatia (Table 2).
Table 2. Summary of the different mine types in different locations.
The lower-side blotch mine, or mine type 1, is an oval tentiform blotch situated on the lower side of the leaflet on one of the leaflet halves (Figure 3a, 3b).
The upper-side blotch mine, or mine type 2, resembles type 1 in appearance (a blotch mine occupying one half of a leaflet) but is situated on the upper side of the leaflet (Figure 3c, 3d). The upper-side midrib mine (Parectopa-like mine), or mine type 3, is an elongated blotch located above the midrib on the upper side of the leaflet, causing upward folding of the leaflet in the middle (Figure 3e–h). In terms of its location on the leaflet, this mine type resembles P. robiniella damage. Mine type 4 (i.e., lower-side edge mine, or Obolodiplosis-like mine) is an elongated blotch situated on the lower side of leaflet next to the leaflet edge, causing strong downward folding and resembling damage caused by the invasive North American locust gall midge O. robiniae (Figure 3j–m). All mine types often begin with a short epidermal tunnel. However, as the mine grows and transitions into a blotch, the preceding tunnel often becomes indistinguishable.
Abundance of Different Mines
In Croatia and Slovenia, the abundance of leaf mines varied significantly between mine types 1–4 (Figure 4, Chi2 =262.51, df = 3, p<0.001).
The highest relative abundance (median of 1.99 per leaf) was observed for mine type 3 (Parectopa-like mine), followed by mine type 4 (Obolodiplosis-like mine) (mean of 1.12 per leaf). Mine types 1 and 2 were the least abundant (mean of 0.53 and 0.14 per leaf, respectively), occurring about four times less frequently than mine types 3 and 4.
Co-occurrence of M. robiniella and P. robiniella Mines
A significantly higher number of M. robiniella mines of all four types were found on leaves without P. robiniella compared to those with P. robiniella, more than would be expected by random chance (Chi2=323.96, df=1, p=1.98e-72) (Figure 5).
A similar pattern was observed for mine type 3 (Chi2=280, df=1, p<0.0001). When comparing the percentage of mine type 3 between the total number of leaflets and leaflets where both species (M. robiniella and P. robiniella) occurred, no significant difference in ratios was found (Chi2 = 3.14, df=3, p=0.37) (Figure 6).
However, when focusing solely on mine types on leaflets where both species (M. robiniella and P. robiniella) co-occurred, there was a significant difference between mine types, which was much greater than would be expected by random chance (Chi2=50.89; df=3; p<0.0001). Mine type 3 had the highest occurrence (n=35), followed by mine type 4 (n=31), mine type 1 (n=5) and mine type 2 (n=1).
Parasitism in M. robiniella Mines
We recorded a statistically lower parasitism rate in mine types 3 and 4 compared to the commonly known mine type 1 (Chi2=6.96, df=2 p=0.03; Chi2=17.44, df=2, p=0.0002) (Figure 7). Parasitism in mine types 3 and 4 was about 6–7%, which is 6.5 times lower than in mine type 1. There was no difference in parasitism between mine types 3 and 4 (Chi2=2.78, df=2, p=0.248).
In total, 16 adult parasitic wasps were recorded in the studied M. robiniella mines in Slovenia and Croatia, belonging to two eulophid species: Pnigalio pectinicornis (L.) (12 adults) and Pediobius saulius (Walker) (4 adults) (Hymenoptera: Eulophidae). Both species were present at a 1:1 ratio in mine type 1 (4 adults each of Pn. pectinicornis and Pe. saulius). In contrast, only Pn. pectinicornis was present in mine type 3 (5 parasitoid adults) and mine type 4 (3 adults).
DISCUSSION
Our study, conducted in forested areas in Slovenia and Croatia, identified four distinct leaf mine types of M. robiniella on R. pseudoacacia. Until now, this moth was largely known in Europe by its lower-side blotch mine (mine type 1) (Whitebread 1990, Seljak 1995, Maček 1999, Ellis 2024); exceptionally a single case when the moth’s larva produced upper side blotch mine situated between the main vein and the leaf edge was recorded in Switzerland (Whitebread 1990). Interestingly, in the studied high-density populations, M. robiniella showed a tendency to mine the upper leaf surface rather than create the typical lower-side blotch mines. In such cases, M. robiniella predominantly situated mines above the midrib, similar to another invasive leaf-mining moth, P. robiniella. However, unlike P. robiniella, whose mines remain flat throughout larval development, the midrib mines of M. robiniella cause an upward contraction of the leaflet along the midrib, resulting in a volumetric structure that is less accessible from the outside.
Indeed, the larvae of some gracillariid moths, particularly (but not exclusively) representatives of the genera Phyllonorycter and Macrosaccus, produce silk threads that attach to the epidermis inside their blotch mines. These silk threads dry and cause the epidermis to fold, making the blotch mines somewhat tentiform, or volumetric. This folding creates a larger internal space, preventing the mine from tearing during expansion (Hering 1951, Maček 1999, Davis and De Prins 2011). Furthermore, the tentiform shape appears to reduce accessibility to natural enemies, thereby protecting the larvae or pupae from being parasitized. Our observations suggest that the upper-side midrib mines of M. robiniella are more strongly folded compared to the lower-side blotches situated on one of the leaflet halves, likely due to greater silk production on the epidermis inside the mine. Another issue that can make M. robiniella to intensively use upper side of leaflets is a strong intraspecific competition as this moth species is known to notably increase population density in the invaded areas (Fodor and Hâruţa 2009).
Another finding is that M. robiniella appears to mimic damage caused by the invasive North American locust gall midge O. robiniae. The main difference is that the curled leaf edge in M. robiniella mines is not thickened, as it is in O. robiniae, which induces galls by manipulating the physiology of the host plant’s leaf, causing it to curl while the larva feeds beneath the curled leaflet edge (Staszak et al. 2023). In lower-side edge mines, M. robiniella larvae feed within the mine, beneath the strongly folded epidermis, causing downward curling of the leaflet edge. This silk-induced folding makes the mine less conspicuous.
Despite creating upper-side midrib mines in areas typically occupied by P. robiniella, M. robiniella does not show clear evidence of competing with P. robiniella for space on leaflets. However, we found that in such mines, the parasitism rate of M. robiniella is significantly lower than that in lower-side blotch mines.
From the limited sampling set available to us from Slovenia and Croatia, only two parasitoid species, Pnigalio pectinicornis and Pediobius saulius, were reared from the leaf mines of M. robiniella. Both are generalist parasitoids native to Europe and commonly associated with various native Gracillariidae species (Csóka et al. 2009). Notably, Pn. pectinicornis and Pe. saulius were present in lower-side blotch mines, for which M. robiniella is commonly known, whereas only Pn. pectinicornis was reared from Parectopa-like and Obolodiplosis-like mines. These two parasitoids exhibit different life strategies: Pn. pectinicornis is an ectoparasitoid, while Pe. saulius is an endoparasitoid of leaf-mining lepidopteran and coleopteran larvae (Bouček and Askew 1968). Notably, only Pn. pectinicornis was found in upper-side midrib and lower-side edge mines, i.e. mines with strongly folded epidermis resulting in mine “closure”. Representatives of Pnigalio do not lay eggs in the larva but near it or even at some distance (e.g., Duncan and Peña 2000, Bernardo et al. 2008). After hatching, the parasitoid larva makes a hole in the cuticle of the host larva and feeds through it while remaining on the host larva’s body. Even if the egg is laid at some distance, the hatched larva actively crawls into the mine to find the host larva and start feeding (Yegorenkova and Yefremova 2012). For Pe. saulius, the infection of the host appears to be a more complex procedure. This species needs to inspect the mine surface, locate the host larva or young pupa hidden inside, pierce it and lay eggs inside the host’s body (Viggiani 1964). Attacking Parectopa-like and Obolodiplosis-like mines could be an energy-consuming task for Pe. saulius, if realizable at all, which may explain why we did not record this parasitoid in strongly contracted mines of M. robiniella. This suggests that M. robiniella may avoid attacks of parasitoids (at least some of them) that it recruited from native gracillariids in Europe.
In Europe, at least 37 hymenopteran species of parasitoids from five families (Braconidae, Chalcididae, Encyrtidae, Eulophidae, Pteromalidae) are known to attack M. robiniella (Davis and De Prins 2011, De Prins and De Prins 2024). In Hungary, where the parasitoid communities of M. robiniella and P. robiniella have been extensively studied, it was shown that all parasitoid species were recruited by these two alien moths from native Gracillariidae, mostly those associated with oaks (Csóka et al. 2009). Interestingly, the parasitoid community of M. robiniella is slightly richer than that of P. robiniella (19 vs. 12 parasitoids), and parasitism rates are higher for M. robiniella (47% vs. 15%, respectively) (Csóka et al. 2009). An early study in Croatia showed that both North American leaf miners are attacked by seven European generalist parasitoid species with slight differences in parasitoid composition, with significantly higher parasitism in M. robiniella (Matošević and Melika 2012). This suggests that, after invading Europe, M. robiniella may have encountered increased parasitism compared to P. robiniella. The heightened pressure from parasitism may have driven M. robiniella to develop adaptations aimed at locating enemy-free space and evading parasitoid attacks. Notably, the North American locust gall midge O. robiniae does not share parasitoids with gracillariids and is only attacked by the specialized parasitoid Platygaster robiniae (Hymenoptera: Platygastridae), which is believed to have arrived in Europe with its host from North America (Buhl and Duso 2008) and does not parasitize gracillariids. Thus, mimicking O. robiniae damage could be beneficial for M. robiniella.
Interestingly, in Europe, M. robiniella has been known solely for its lower-side blotch mines (Whitebread 1990, Seljak 1995, Maček 1999, Davis and De Prins 2011). Matošević (2007) conducted a detailed study of the biology, ecology and parasitoids of M. robiniella in Croatia between 2004 and 2006 and observed exclusively lower-side blotch mines, with no upper-side midrib mines recorded. In contrast, in the native range (North America), M. robiniella has also been documented to produce upper-side midrib mines (Parectopa-like mines) (Braun 1908, Weaver and Dorsey 1967) and O. robiniae-like mines.
Our study has several limitations. The survey was conducted only in forested areas and only in two countries within the M. robiniella-invaded range, and it is possible that different mine types may also occur in urbanized areas, including in other European countries. Only high-density populations were considered, and thus, it remains unclear how low-density populations of this invasive moth behave in Europe. The number of parasitoid individuals reared from different mine types of M. robiniella was rather small, resulting in the identification of only two eulophid species, whereas the parasitoid assemblage of M. robiniella in the invaded range is much larger (Csóka et al. 2009, Matošević and Melika 2012, De Prins and De Prins 2024). Further studies involving larger samples of leaf mines and parasitoid rearing over multiple years are needed to confirm M. robiniella's strategy of seeking refuge from parasitoids by exploiting different parts of leaflets for mining. Finally, it would be important to clarify whether constructing alternative mines (mimicking the damage of other endophagous insects) is a strategy observed over time in the invaded range or whether it is also evolving in the native range (some parts of North America). Long-term documentation of damage patterns would help elucidate the life history and evolutionary adaptations of M. robiniella in both its native and invaded ranges. Citizen science platforms, such as iNaturalist, which store photographs of leaf mines from both continents over time, could provide valuable data for exploring this question.
CONCLUSIONS
Four leaf mine types were described from highly dense populations of the North American leaf-miner Macrosaccus robiniella in Slovenia and Croatia in 2023. Mine type 1 (i.e., lower-side blotch occupying one of the leaflet halves) is the damage by that the species was known since its first detection in Europe. Mine type 2 is similar to mine type 1, but the mine is located upper side of one of the leaflet halves. Mine type 3 (blotch above the midrib on the upper side of the leaflet) and 4 (narrow blotch at the edge, causing strong downward folding) resemble the damage of two other invasive insects from North America, i.e., the gracillariid Parectopa robiniella and the gall midge Obolodiplosis robiniae, respectively. The mine types 1 and 2 were least present in the studied populations. Mine types 3 and 4 were up to four times more abundant than mine types 1 and 2. Parasitism rate was 6.5 times lower in mine types 3 and 4 compared to mine type 1.
Author Contributions
NIK, SG and MdG conceived and designed the research, NIK and SG carried out the field measurements, NIK and OVK performed laboratory analysis, NIK and MdG processed the data and performed the statistical analysis, NIK, MdG and BP secured the research funding, supervised the research and helped to draft the manuscript, NIK, SG, OVK, DM, BP, and MdG wrote the manuscript.
Funding
The study was supported by the core research group Forest Biology, Ecology and Technology (P4-0107) of the Slovenian Research Agency and the Administration for Food Safety, Veterinary Sector and Plant Protection at the Ministry of Agriculture, Forestry and Food of the Republic of Slovenia [field work], as well as by the Russian Science Foundation (grant No. 22-16-00075-P) [parasitism assessment].
Acknowledgments
The authors thank Jan Nagel for carefully checking the English in the manuscript and for suggesting improvements.
Conflicts of Interest
The authors declare no conflict of interest.
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