Arboreta serve as effective tools for identifying alien insect pests and novel trophic associations. In this study, we used an arboretum in Slovenia to survey woody plants and identify both alien and native leaf miners. The leaves and twigs of 50 woody plant species and their cultivars were examined for characteristic damage. We used an integrative approach that combined identification based on leaf mines and DNA barcoding of the larvae and pupae found in the mines. In total, 62 leaf-mining species were identified, including eight alien species, of which the heliozelid Coptodisca lucifluella (Clemens, 1860) and the agromyzid Cerodontha unisetiorbita Zlobin, 1992 were documented for Slovenia for the first time. Additionally, three presumably native Gracillariidae moths Phyllocnistis labyrinthella (Bjerkander, 1790), P. ramulicola Langmaid & Corley, 2007 and P. saligna (Zeller, 1839) represented the first record for Slovenia. Furthermore, we documented 23 novel-to-science trophic associations, 20 of which involved native insects and alien woody plants, primarily from Asia. This study highlights the importance of arboreta and botanical gardens for the interception of invasive alien insects and the early detection of trophic shifts of native insects to alien plants, which can aid in predicting their potential spread.

Here, we report the first detection of the North American leaf-mining moth Chrysaster ostensackenella (Fitch, 1859) (Lepidoptera: Gracillariidae) on North American black locust Robinia pseudoacacia (Fabaceae) in Primorsky Krai (the Russian Far East) in July 2022. Overall, six moths were reared from the leaf mines and identified based on adult morphology (forewing pattern and male genitalia) and three of them were DNA barcoding. Description of the leaf mines that allowed us to distinguish the damage of Ch. ostensackenella from other gracillariids associated with R. pseudoacacia is provided. The phylogeographic analysis comparing the DNA barcodes from Russia with those from other invaded countries in Europe (Italy) and East Asia (South Korea and Japan) and from the native range (North America) was performed. Intraspecific genetic diversity reached 3.29%. Altogether, 10 haplotypes were revealed among 21 studied specimens in the Holarctic. The detection of one haplotype common for Japan and the USA (North Carolina) suggests that the invasion to East Asia could have happened from the USA directly, rather than through Europe. A shared haplotype defined for Japan and the Russian Far East points at a possible moth species’ spread to Primorsky Krai from earlier invaded Hokkaido. Further distribution of Ch. ostensackenella in East Asia and Europe is expected, bearing in mind the wide planting of R. pseudoacacia in these continents. Furthermore, an accidental introduction of the moth to the Southern Hemisphere, where black locust was introduced, is not ruled out.

Gracillariidae is one of the richest families of leaf mining moths, known by its ornamental and orchard plant pests expanding their primary ranges. We here provide a revised checklist of Gracillariidae (Lepidoptera) of Slovenia that presently accounts for 123 species. Among them, four species, Dialectica imperialella (Zeller, 1847), Phyllonorycter abrasella (Duponchel, 1843), Ph. trifoliella (Gerasimov, 1933), and Phyllocnistis valentinensis M. Hering, 1936, are new records for the country. The distribution of the other three species in Slovenia, Caloptilia honoratella (Rebel, 1914), Dialectica scalariella (Zeller, 1850), and Ph. messaniella (Zeller, 1846), is clarified. For the above seven species, short synopses of the bionomics, a current range, and images of biotopes, adult moths and their genitalia are provided. For P. valentinensis sampled at a larval stage, the DNA barcode was obtained to confirm the species identification. Given the known distribution of some of the newly recorded moths in Europe, we believe that these species do not represent a new invasion but rather are discoveries of native species, except for the newly documented Ph. trifoliella in Slovenia, which is likely to be an alien species for the country.

The aim of this study was to determine whether opportunistic citizen science can support the detection of life history traits in invasive insects. Using the invasive leaf-mining micromoth Macrosaccus robiniella (Clemens 1859) (Lepidoptera: Gracillariidae) as a model species, we analyzed data from iNaturalist submitted by citizen scientists to assess the variability in its leaf mines on its native host, Robinia pseudoacacia L., 1753 (Fabaceae), across both the moth’s invaded (Europe, North America–Eastern United States) and native range (North America–Southern and Western Unites States, Eastern Canada). We examined 86,489 photographs collected over the past 20 years to compare the occurrence and proportions of different M. robiniella leaf mine types between invaded and native ranges using three search variants: (I) M. robiniella, (II) all endophagous invasive insects associated with R. pseudoacacia, and (III) the host plant itself. The first two datasets revealed differences in the ratio of leaf mine types between Europe and North America (when analyzed separately for native and invaded areas), whereas the third dataset showed no significant differences in either the presence or proportion of mine types between invaded and native ranges. Leaf mine types atypical of M. robiniella, which resemble damage caused by other invasive insects such as Parectopa robiniella Clemens, 1863 (Lepidoptera: Gracillariidae) and Obolodiplosis robiniae (Haldeman, 1847) (Diptera: Cecidomyiidae)—also associated with R. pseudoacacia—have been observed in Europe for at least a decade. Our main conclusion is that, when investigating the life history traits of invasive herbivorous insects, focusing data collection on the host plant rather than on the insect species alone can reduce biases associated with opportunistic citizen science and help reveal true ecological patterns.

The paper reveals 113 new records of Eriogaster catax (Linnaeus, 1758) from 78 localities in Slovenia. Its known distribution was extended from 44 to 56 UTM grid squares. Most of the new records come from the Primorska region. The most valuable extension of the currently known distribution is in north-eastern Slovenia: at the Ledava, Mura and Drava Rivers; in eastern Slovenia: the Kozjansko region and along lower stretches of the Sava River. The species was recorded for the Bela krajina region for the first time. Additional records were collated also in the Notranjska region (Cerkniško Lake and Pivka lakes), at southern slopes of Mt. Nanos and in the Dragonja River valley. Using all the data, an analysis of phenology and vertical distribution of species was conducted. Observations of larval stages of E. catax were made from late March until mid-June, while adults were observed from mid-September until early November. Altitudinal distribution varies between 0 and 960 m a. s. l. The median of vertical distribution is at 258 m a. s. l. Half of the records were made between 166 and 420 m a. s. l. We conclude that the distribution of the species in Slovenia is still inadequately known.

The Siberian moth, Dendrolimus sibiricus Tschetverikov, is one of the most destructive conifer pests in Northern Asia, causing severe ecological and economic losses. In Russia, its range overlaps with that of the closely related pine-tree lappet Dendrolimus pini (L.), and this raises the potential for hybridization and complicates accurate identification, particularly in the context of the potential westward expansion of D. sibiricus. Here, we present the first comprehensive morphometric analysis of male genitalia aimed at distinguishing these two major forest pests and their hybrids. The study was based on D. sibiricus and D. pini specimens collected during the last 130 years (1894–2024) across Europe and Asia, including their hybrids reared indoors by crossing D. pini females with D. sibiricus males in 1956 and preserved in the collection of the Zoological Institute of the Russian Academy of Sciences (St. Petersburg, Russia). Overall, 70 permanent genitalia slides were prepared (33 D. sibiricus, 33 D. pini, and 4 hybrids), and the following genital structures were measured: valva and harpe length, aedeagus width and length, and cornuti length. Dendrolimus sibiricus had significantly larger genital structures compared to D. pini: 74% longer harpe, 32% longer valva, and a 28% wider and longer aedeagus. In contrast, in D. sibiricus cornuti were 21% shorter than in D. pini. Hybrids displayed intermediate values for valva, harpe, and aedeagus lengths, and for these parameters, they significantly differed from both parental species. The following diagnostic indices were suggested to distinguish between the two species and their hybrids: Harpe Length/Valva Length Index (HL/VL) and Cornuti Length/Aedeagus Length Index (CL/AL). Decision-tree analysis identified HL/VL as the strongest predictor for separating the parental species and the Combined Genital Proportion Index (CGPI), which integrates harpe, valva, aedeagus, and cornuti lengths, as the strongest predictor for identifying hybrids. The morphometric criteria developed here have practical applications for monitoring programs and quarantine diagnostics, particularly in sympatric zones and regions at risk of D. sibiricus expansion.