According to the literature search, a total of 349 alien species were identified (Suppl. material 1), distributed within 261 genera and 97 insect families (Fig. 1). The current number of alien insects of Cyprus has tripled (204% increase) since their first treatment (DAISIE 2009; Roques et al. 2010; Martinou et al. 2020). Out of these species, only one can be found in the EPPO A1 list of pests recommended for regulation as quarantine pests, namely Spodoptera litura (Fabricius, 1775), while 12 can be found in the EPPO A2 list (Suppl. material 1).

Figure 1.

Number and percentage of alien insect species by order detected in Cyprus.

Of the total number of species, most of them are “confirmed alien species” to the island (242 species = 69%), while more than one fourth (97 species = 28%) are “cryptogenic” and ten species (3%) were classified as “questionable” (Fig. 2).

Figure 2.

Status of alien insects species by order detected in Cyprus, classified as “confirmed alien” (truly demonstrated to be non-native to Europe and Cyprus), “cryptogenic” (species of unknown origin) and “questionable” (species whose status should be further investigated).

The largest percentage of “confirmed alien” insect species originates from the Indomalayan biogeographic realm (29%), followed by the Eastern Palearctic (15%). Each of the Afrotropical and Australian realms contribute 14% of “confirmed alien species”. Nearly one fifth of “confirmed alien species” originate from the New World, being native to the Neotropical (12%) and Nearctic (10%) realms. Species originating from the tropics and subtropics (4%), as well as “confirmed alien species” within the Western Palearctic (3%), had the lowest representation within the dataset (Table 1).

Almost half of the alien insects in Cyprus are classified as phytophagous (48%). Almost one in four are detritivores (24%), while the remaining quarter accounts for parasites, parasitoids (grouped) (17%) and predators (11%) (Fig. 3). Only one species, the ant-like beetle Anthicus crinitus La Ferté-Sénectère, 1849 was recorded as of unknown feeding habits (Denux and Zagatti 2010) and was subsequently excluded from the analysis.

Figure 3.

Trophic guilds of alien insects of Cyprus. The number of species and their percentages are shown on the pie chart. Further information on phytophagous insects and their classification is provided in the box depicting the overall number of species in each ecofunctional group.

Phytophagous alien insects were further classified into six functional groups (Table 2). Half of the represented phytophagous insects have sucking mouthparts, predominantly Hemiptera (92%) and some Thysanoptera (8%). Almost one third chew on leaves, stems and other soft tissues, mostly Coleoptera (57%) and Lepidoptera (30%). All leaf-, seed-gallers and pollinators are hymenopterans, whereas leaf-miners are equally divided between Diptera (Cecidomyidae) and Lepidoptera (Gelechiidae and Gracillariidae). Lastly, the majority of wood-feeding insects were from the order Coleoptera with just one moth from the family Castniidae (Table 2, Fig. 3).

Overall, most of alien insects (70%) seem to have established (producing viable, self-reproducing populations) on the island. Only two species, Octodonta nipae (Maulik, 1921) and the yellow fever mosquito Aedes aegypti Linnaeus, 1762 are considered to have been eradicated (1%). The Groundnut bruchid Caryedon serratus (Olivier, 1790) and the mango seed weevil Sternochetus mangiferae (Fabricius, 1775) were unintentionally introduced, but failed to establish (1%). The red scale parasitic wasp Aphytis holoxanthus DeBach, 1960 was intentionally released, but failed to establish and nine species (3%) are considered doubtful or dubious. More information regarding their establishment status is given below. Nevertheless, information about the establishment of more than one quarter of alien insects (25%) remains unknown (Fig. 4).

Figure 4.

Number and percentage of alien insect species by order detected in Cyprus according to their establishment status, classified as “established” (sustaining populations on the island); “failed to establish” (unintentionally-introduced, but failed to establish); “released, but failed to establish” (intentionally released, but failed to establish); “eradicated” (confirmed eradication); “Doubtful” (species potentially wrongly identified or records regarded dubious); and “Unknown” (establishment status could not be assigned because of lack of data or species or reported only once).

Collectively, 32 alien biological control agents of crop pests have been intentionally introduced to Cyprus, accounting for approximately 9% of all alien insects, comprising five alien Coleoptera (16%) and 27 Hymenoptera (84%). Within the Hymenoptera, 17 species (63%) belong to the superfamily Chalcidoidea, nine (33%) to Ichneumonoidea and one species (4%) to the family Vespidae (Suppl. material 2).

Of the total species list, 26 species (81%) have established populations on the island. Aphytis holoxanthus, a parasitoid released for the control of scale insects, failed to establish soon after its import and release (Greathead 1976). The establishment status of four species (13%) is unknown. The presence of Cirrospilus ingenuus Gahan, 1932, parasitoid of citrus leaf miners, is considered doubtful being catalogued both as established, as well as not established (Gerber and Schaffner 2016).

Most of the introduced biological control agents have been released for control of pests in citrus (59%), potato (30%) and olive (9%) pests (Fig. 5). A single record suggesting the introduction of the yellow jacket Vespula germanica to the island (Morris 1937) needs confirmation. Half of these biological control agents were imported to the island during the decade 1951–1960, against potato and citrus pests (Fig. 5). From the searches conducted to date, it appears that there have been no official records of biological control agents intentionally released into the wild since the beginning of the 21^st century. The introduction year of Rhyzobius forestieri (Mulsant, 1853), Forestier’s ladybird, is unknown. Although Gerber and Schaffner (2016) cite an annual report of the Cyprus Agricultural Research Institute published in 1984, Orphanides (1988) does not mention the species in his article as a biological control agent of Saissetia oleae (Olivier, 1791) in Cyprus. Thus, the presence of R. forestieri on the island is considered dubious.

Figure 5.

Introduction history of imported biological control agents to Cyprus. The graph shows the number of species per decade released to control citrus, olive, potato and other pests. The number of Coleoptera and Hymenoptera species introduced during each decade are shown in the box over the graph.

Only 19 species (5% of total alien insects in Cyprus) were identified as invasive alien species, having negative impacts upon biodiversity and ecosystem functions (Fig. 6). Thirty-seven species (10%) had a positive socio-economic impact, negatively affecting invasive alien host-animal or -plant species, being pollinators or contributing towards the biological control of injurious or alien pest species. The majority of species with recorded negative impacts affected socio-economic parameters (135 species – 38%). These species were predominantly “agricultural and horticultural pests” (61 species – 38%), “forestry and urban tree pests” (42 species – 27%), “stored product and infrastructure pests” (40 species – 25%) and “insects affecting human and animal health” (16 species – 10%) (Fig. 6).

Figure 6.

Known registered impacts of alien insects in Cyprus. The number of species classified as data deficient, having positive economic or negative environmental or socio-economic impacts, as well as their percentage are shown in the left pie chart. Negative socio-economic impacts are further divided into alien insects identified as “Outdoor agricultural and horticultural pests”, “Pests of protected horticulture”, “Stored product and infrastructure pests”, “Forestry and urban tree pests” and “Arthropods affecting human and animal health” (right pie chart). The total number of species in this figure does not total to 349 as species displaying both positive and negative impacts or that could be assigned to more than one subcategories of negative socio-economic impacts.

Most of the alien insects of Cyprus (170 species – 47%) were catalogued as data deficient due to the lack of studies addressing their impacts, the lack of observed impacts or the low quality of evidence for impacts (Fig. 6).

Coleoptera represent the most species-rich order of alien insects on Cyprus comprising more than 100 alien species (Fig. 1). Five families of Coleoptera, namely Nitidulidae (10%), Dermestidae (10%), Chrysomelidae (10%), Ptinidae (10%) and Curculionidae (9%), contain almost half of the alien beetles found in the island. These families include solely detritivores and phytophagous species found in stored products, such as the carpet beetles Trogoderma granarium Everts, 1898 and Trogoderma versicolor (Creutzer, 1799), the seed beetles Bruchus rufimanus Bohemann, 1833 and Callosobruchus chinensis (Linnaeus, 1758), as well as representatives of the genus Sitophilus Schoenherr, 1838 (Morris 1937; Georghiou 1977). Interestingly, the only references to Sitophilus sculpturatus (Gyllenhal, 1838) in Europe concern Cyprus nearly a century ago, when the species was reared from Eugenia jambolana (L.) Skeels seeds imported from South Africa (Morris 1937; Georghiou 1977). Nitidulids have been identified both as herbivores and detritivores feeding on ripe and rotten fruit (Georghiou 1977; Jelínek et al. 2016). In addition, these families include some easily detectable major pests of ornamental plants, such as the destructive red palm weevil Rhynchophorus ferrugineus (Olivier, 1790) (Kontodimas et al. 2006), but also the leaf beetle Chrysolina americana (Linnaeus, 1758), found damaging five aromatic Lamiaceae, including three species native to the island (Hadjiconstantis and Zoumides 2021). Despite the small body size of most species in the aforementioned families, their predominance in the list of alien Coleoptera may well be attributed to their peridomestic lifestyle and negative economic impacts on stored products, crops and ornamentals which reinforce the need for studies addressing their identification and approaches for mitigation of their negative impacts.

As is the case with Greece (Demetriou et al. 2021), Hemiptera are predominantly represented by scale insects (Coccoidea) (44%), followed by aphids (28%) and whiteflies (10%). The high numbers of alien Sternorrhyncha are strongly correlated to their unintentional transport as contaminants on infested plant material (Rabitsch 2010a), but also biological traits facilitating successful biological invasions, such as their minuscule body size, their ability to reproduce both through parthenogenesis and sexual reproduction, as well as their high fecundity (Coeur d’Acier et al. 2010; Pellizzari and Germain 2010). Furthermore, their host plants range includes a wide variety of economically important species increasing detection probabilities (Coeur d’Acier et al. 2010), although their ability to exploit “hidden” microhabitats (e.g. undersides of leaves, shoot and bark crevices) hinder their interception during phytosanitary inspections (Pellizzari and Germain 2010). Improving phytosanitary measures and quarantine inspections, while recognising the challenges, may minimise the import of alien Hemiptera to the island as most species have been associated with common alien ornamental and agricultural plants (Georghiou 1977; Şişman and Ülgentürk 2010; Ülgentürk et al. 2015).

The superfamily Chalcidoidea, holds 71% of all recorded alien hymenopterans. The superfamilies Ichneumonoidea and Formicoidea follow, accounting for 14% and 12% of species, respectively. More than one third of alien Hymenoptera have been intentionally introduced to the island. Introduction pathways of the remaining Hymenoptera are currently unknown and most probably reflect unintentional introduction alongside their hemipteran hosts [e.g. Psyllaephagus bliteus Riek, 1962, an Australian parasitoid of the red gum lerp psyllid Glycaspis brimblecombei Moore, 1964; (Karaca et al. 2017)] or host plants [e.g. Pleistodontes imperialis Saunders, 1882, a mutualistic pollinator of Australian Ficus rubiginosa Desf. & Vent.; (Compton et al. 2020a)]. Nine species of alien ants have been collected from Cyprus, including the dubious records (possible misidentifications) of Cardiocondyla nuda (Mayr, 1866) (Bernard 1956), Trichomyrmex destructor (Jerdon, 1851) and the fire ant Solenopsis geminata (Fabricius, 1804) (Georghiou 1977; Collingwood et al. 1997; Salata et al. 2019). According to Salata et al. (2019), the Pharaoh ant Monomorium pharaonis (Linnaeus, 1758), Nylanderia jaegerskioeldi (Mayr, 1904) and the fire ant S. geminata are responsible for the elimination of native species within invaded habitats due to the aggressive behaviour of the invasive ants. Although the fire ant S. geminata is only known from an old, possibly erroneous literature record, Cyprus is stated to be within the species’ known distribution (Collingwood et al. 1997; Dr Christos Georgiadis, pers. comm.).

All but one of the alien Lepidoptera are moths, with half of species falling under Pyralidae (19%), Gelechiidae (16%) and Tineidae (16%). These families include minute species commonly identified as stored product and household pests, such as the snout moths Corcyra cephalonica (Stainton, 1866) and Ephestia elutella (Hübner, 1796) and gelechiid moths Pectinophora gossypiella (Saunders, 1844) and Sitotroga cerealella (Olivier, 1789) (Morris 1937; Georghiou 1977). The sole exception is Papilio demoleus Linnaeus, 1758, a large alien butterfly reported only recently from Cyprus, but its impact on native biodiversity is still unknown (John et al. 2021, 2022).

Due to the geographic location of Cyprus, surrounded by Europe, Africa and Asia and the lack of literature data, the status of ten species was treated as “questionable” (Fig. 2). The soldier fly Pseudodoros nigricollis is believed to be native to the East Mediterranean and Afrotropics (van Eck and Makris 2016; André van Eck, pers. comm.). The recent discovery of the species on the island and the general lack of knowledge surrounding the distribution of Syrphidae in the Near East pose difficulties in assessing the native or “alien” status of P. nigricollis in Cyprus (André van Eck, pers. comm.). In addition, the “cryptogenic” status of its associate host Hyalopterus pruni (Geoffroy, 1762) and its observed relationship with both native (Phragmites australis and Prunus spp.) and alien host plants (Musa sp.), further complicate this assessment (André van Eck, pers. comm.). The date stone beetle, Coccotrypes dactyliperda, has been regarded as alien to Europe originating from some undetermined tropical or subtropical area (Sauvard et al. 2010). A more recent study characterises this species as of Middle Eastern origin (Spennemann 2019), but its main host plant Phoenix dactylifera L. is regarded as introduced to Cyprus (Christofides 2017). The planthopper Jacobiasca lybica probably originates from northern Africa, but is widely distributed in the Mediterranean (Mifsud et al. 2010). In Cyprus, the first and only record for the species dates back to 1967 when J. lybica was collected on grapes (Georghiou 1977). Previous studies failed to locate the species in the island (Lindberg 1948) and its “alien” status has been regarded as doubtful (Mifsud et al. 2010). The Asian moth Dichelia cedricola, has been labelled as alien to Europe (Lopez-Vaamonde et al. 2010). The species is a renowned pest of Cedrus spp. causing serious defoliation of Cedrus libani A. Rich. in neighbouring Lebanon and Turkey (Nemer et al. 2015). In Cyprus, management of the species in Cedar Valley, where the endemic cedar C. brevifolia occurs, was initiated a decade ago (Gatzogiannis et al. 2010). The isolation of Cedar Valley, situated deep within the islands’ Troodos mountain range, the reduced available habitat for D. cedricola and nativity of similarly perceived alien associate of cedar C. cedri, may indicate that, not only D. cedricola could be native to Cyprus, but also consist an endemic subspecies.

In relation to Hymenoptera of “questionable” status, six species are presented. The Aphelinidae Aphytis coheni has been reported as of both western and south-eastern Asian origin (Avidov et al. 1970; Gerber and Schaffner 2016; EASIN 2021). Despite being intentionally introduced to the island as a biological control agent for Lepidosaphes beckii (Newman, 1869), the type-locality of A. coheni in neighboring Israel raises doubts about its region of ancestry (Gerber and Schaffner 2016). In Europe, Scutellista caerulea was released in France and Greece against Saissetia oleae (Olivier, 1791) (Gerber and Schaffner 2016). The species has been collected from Cyprus since 1931 (Wood 1963; Georghiou 1977), but there is no evidence of intentional introduction to the island. A native population of this African species already existed in Crete prior to the species’ intentional introduction (Gerber and Schaffner 2016). Taking into account the proximity of both Crete and Cyprus to northern Africa, S. caerulea may indeed be native to Cyprus. The same principle applies to both African Encyrtidae Diversinervus elegans and Microterys nietneri released in Europe as biological control agents, but collected in Cyprus without a recorded history of intentional introductions (Wood 1963; Orphanides 1988; Gerber and Schaffner 2016). Regarding Vespula germanica, as stated in Morris (1937) “is said to have been introduced to the island some years ago in hopes of reducing the number of flies”. To date, this statement remains unconfirmed. Despite being widespread and common in the Western Palearctic, V. germanica has been introduced to various islands, such as Iceland, Madeira and Canary Islands (Rasplus et al. 2010; Beggs et al. 2011). It is, therefore, not possible to confirm the native or “alien” status of V. germanica in Cyprus. Nevertheless, this hypothesis could be tested through molecular population genetics. Finally, Xylocopa pubescens is perhaps the most common carpenter bee species observed in Cyprus. Despite extensive research on the island’s bee fauna conducted during the 1940s and 50s by Georgios Mavromoustakis, the species was not recorded (Mavromoustakis 1949[1948], 1951, 1952). Earliest records of this large and easily identifiable species in Cyprus emerged after the 1990s (Terzo and Rasmont 2014; Varnava et al. 2020). There are no known cases of intentional introduction of X. pubescens or other bees on the island (Cyprus Veterinary Services – Ministry of Agriculture, Rural Development and the Environment, pers. comm.). The import of Apoidea from EU countries must be registered in the TRACES platform (https://food.ec.europa.eu/animals/traces_en), while introductions from third countries are mediated by health certificates and inspections upon arrival from custom controls. The Ethiopian ancestral origin of X. pubescens, recent detection of the species in 2012 from Athens, Greece (Terzo and Rasmont 2014) and its positive role as a pollinator of greenhouse crops in Israel (Sadeh et al. 2007), may reflect a recent range expansion or perhaps its introduction to the island for agricultural purposes.

Species originating from biogeographic realms surrounding the island, i.e. the Eastern and Western Palearctic, the Afrotropics and tropical/subtropical regions, account for more than one third (36%) of the “confirmed alien” insects of Cyprus. However, introductions from remote regions seem to have a strong influence on the composition of the island’s “confirmed alien” entomofauna, with Indomalaya accounting for more than one fourth (29%) of “confirmed alien species” of insects (Table 1). Asian species, originating from Eastern Palearctic and Indomalaya represent the majority of introduced taxa (44%). This may derive from increased imports from Asian countries, such as China, Israel and Turkey, although the island’s largest trading partners correspond to European countries, predominantly Greece and Italy (Trend Economy 2021). Therefore, Greece and Italy may contribute to the introduction of alien species to Cyprus, hidden as stowaways in shipment or avian cargo (Inghilesi et al. 2013; Avtzis et al. 2017; Demetriou et al. 2021).

As trade plays a crucial role in the introduction of alien species (Hulme 2009; Seebens 2019), enhancing biosecurity for regions with high import rates could be advantageous. This could include ongoing effective inspection mechanisms deployed through customs and border controls, at entry points such as airports and harbours, alongside implementation of specialised inspection protocols according to cargo type and origin.

The diversity of functional groups represented within each insect order reveals the range of alien insects of Cyprus. Detritivorous species are predominantly beetles (62%). To a lesser extent are Lepidoptera and Psocodea (12% each), followed by Diptera (6%) and common house intruders in the orders Blattodea and Zygentoma (6% and 3%, respectively). The overwhelming majority of parasitic taxa are Hymenoptera (79%), mostly wasps combating agricultural pests of economic significance, such as the Neotropical braconid Apanteles subandinus Blanchard, 1947 tackling the common and destructive moth Phthorimaea operculella (Zeller, 1873) (Georghiou 1977; Gerber and Schaffner 2016) and others discussed below. These are followed by just a few animal parasites in the orders Siphonaptera and Phthiraptera, as well as some parasitic flies, such as Trichopoda pictipennis Bigot, 1876 (Kazilas et al. 2020; Dios et al. 2021). Most of the predatory species belong to Coleoptera (50%) and ants (26%). Predatory behaviour of alien insects has received little to no interest in Cyprus, except from alien Coccinellidae (Wood 1963). Five out of six alien ladybirds found in the island have been intentionally released as biological control agents.

Phytophagous insects are mainly sap-feeding Hemiptera (45%) and Coleoptera (24%) feeding on leaves and stems of plants (Fig. 3; Table 2). Gall formers (gallers) are mostly host-specific to alien ornamental plants, such as Eucalyptus spp. infested by the Australian leaf gallers Leptocybe invasa Fisher & La Salle, 2004 and Ophelimus maskelli (Ashmead, 1900) and alien Ficus spp. hosting a wide variety of fig wasps (Compton et al. 2020a; Demetriou et al. 2022; Demetriou et al. in press). Regarding wood-feeding insects, the only exception to Coleoptera is the Neotropical moth Paysandisia archon (Burmeister, 1879) (Table 2). The moth was discovered in Paphos and Limassol (Cyprus) boring in Chamaerops humilis L., Phoenix roebelenii O’Brien and Washingtonia filifera (Lindl.) H.Wendl. palms imported from Italy (Vassiliou et al. 2009). The infested plant material was destroyed, but due to the extended biological cycle of the insect, surveys continued until the end of the detection year (Vassiliou et al. 2009). Since then, the palm moth has been sighted once at Zygi (Larnaca) (John and Skule 2016). This demonstrates that wood boring insects can expand into new regions outside their native range even during their immature stages, which can be transported when inside their host plants (later used for planting) or even with timber (Cocquempot and Lindelöw 2010; Demetriou et al. 2021). Thus, in addition to phytosanitary measures reinforced against Hemiptera and species responsible for visually detectable infestation signs (e.g. galls, leaf mines, bite marks), monitoring imported plants and furniture for signs of infestation by wood-feeding insects constructing galleries could be informative for as a biosecurity measure.

Detritivorous species are mainly associated with household commodities and are, thus, probably introduced to the island through international commerce of stored goods. Phytophagous insects may have reached Cyprus through the introduction of their host plants, as indicated for Hemiptera (Rabitsch 2010a), but also Hymenoptera. Although introduction pathways in Cyprus are largely unknown, these assumptions are in accordance with scientific evidence pinpointing the introduction pathways of terrestrial invertebrates in Europe (Peyton et al. 2019, 2020; Pergl et al. 2020). In particular, primary pathways include stowaways and contaminants of food, plants and nursery material (Pergl et al. 2020), while secondary pathways also include the transportation of habitat material, such as soil and vegetation (Pergl et al. 2020). An extended literature survey, not only on a local, but also continental scale, would help identify the main introduction pathways of alien insects to Cyprus. Furthermore, this information could provide information for the design of specific investigation protocols, according to the feeding habits of alien insects and the taxonomic groups present in each feeding guild, to underpin biosecurity.

A total of 245 alien insect species have established viable, reproducing populations on the island (Fig. 4). Species that failed to establish include the seed-beetle Caryedon serratus, a species considered unable to establish itself both in the wild and storehouses (Yus-Ramos et al. 2014) and the mango seed weevil Sternochetus mangiferae reared once from mango imported from Sri Lanka in 2011 (Biodiversity of Cyprus 2022). As stated earlier, although Aphytis holoxanthus was introduced to Cyprus from Israel in 1959 and 1960, it failed to establish and provide any control of Aonidiella aurantii (Maskell, 1879) (Gerber and Schaffner 2016).

Although reported as present in Cyprus from Burmeister (1939), the presence of the carabid beetle Laemostenus complanatus (Dejean, 1828) is considered unlikely (Austin et al. 2008). Despite their extensive survey work, Austin et al. (2008) failed to detect the species on the island, while it has also been stated that the species is not present in Turkey and the Middle East (Casale 1988). As explained earlier, Rhyzobius forestieri is also considered doubtfully present as it has not been mentioned in any literature dealing with the Coccinellidae of Cyprus and their use as biological control agents of scales (Wood 1963; Orphanides 1988; Özden et al. 2006). Lastly, records of Oligota parva Kraatz, 1862 and Nomius pygmaeus (Dejean, 1831) also seem to be doubtful as the species have been reported only from Baudi di Selve (1870) and Fauvel (1889), respectively. Since then, no records of the species have been found and their presence on the island has not been confirmed (Bordoni 2010). The only dubious record referring to Hemiptera concerns Ploiaria chilensis (Philippi, 1862) (Putshkov and Putshkov 1996; Rabitsch 2010b). The remaining four doubtful species are the chalcid wasp Cirrospilus ingenuus (mentioned above) and three ant species; Cardiocondyla nuda, Trichomyrmex destructor and Solenopsis geminata (Bernard 1956; Georghiou 1977; Collingwood et al. 1997; Salata et al. 2019). The alien ant fauna of Cyprus will be examined in greater detail during the following years (Demetriou et al. in prep).

Management of alien species is easier and more effective during the initial stages of biological invasion than later in the process (Simberloff et al. 2013). In Cyprus, this was the case with Octodonta nipae, a flower beetle which was found on young leaves of ten Syagrus romanzoffiana (Cham.) Glassman palms in Limassol and was rapidly eradicated (Vassiliou et al. 2011). Host-plants were potted and maintained as transplants in urban habitats of Germasogeia (Limassol), and infested plants and areas at risk (e.g. gardens, warehouses and production sites) were immediately treated with chemicals and monitored for a period of eight months “due to the long and cryptic life cycle of this palm insect pest” (Vassiliou et al. 2011). Overall, the rapid implementation of measures against O. nipae is considered to have resulted in successful eradication of the species on the island. The second invasive alien insect which was considered as eradicated is the yellow fever mosquito Aedes aegypti, although it was predicted through horizon scanning to have a high potential for arriving again in the future (Peyton et al. 2019, 2020). However, the species was rediscovered in September 2022 at Dromolaxia, Larnaca District almost one century after it was last reported as present in the country by Aziz (1934). The presence of established populations that might have escaped past eradication efforts or the unintentional re-introduction of the yellow fever mosquito in Cyprus need to be confirmed. Nevertheless, systematic mosquito surveillance in the Akrotiri Peninsula and surrounding regions since 2012 has failed to detect the species thus far (Martinou et al. 2022a). Aedes albopictus (Skuse, 1894) has also been recently (October 2022) recorded at six locations in Limassol District (Martinou et al. 2022b; Christou et al. in press). Due to the most recent discovery of these invasive alien mosquito species (exceeding the data collection period), these records are not presented in our checklist, but will be added to the database.

The establishment status of 90 alien insect species (25%) is unknown, due to the collection of single specimens, incomplete record files, as well as data deficiencies in recovered, provided or investigated literature. Thus, further research is necessary to confirm the presence of these insects on the island. Material sampling and identification of alien species in museum and personal collections, as well as communication with experts and digitalisation of grey literature could assist these endeavours. For example, little is known about the establishment status of alien Phthiraptera, where all species were catalogued as “unknown”. These data deficiencies could be addressed through the construction and maintenance of databases with observations from veterinarians and municipal veterinary services. Knowledge gaps also appear in Coleoptera, Hemiptera and Lepidoptera where the establishment status was considered as unknown for 38%, 29% and 23% of cases, respectively.

Releases of alien insects as biological control agents in Cyprus reached a peak during the 1960s (Fig. 5; Suppl. material 2). During this decade, half of the released classical biological agents were introduced to the island, to tackle the increased damage caused to cultivations, particularly due to citrus pests, such as the hemipterans Chrysomphalus aonidum (Linnaeus, 1758), Lepidosaphes beckii and Planococcus citri Risso, 1813 (Wood 1963; Gerber and Schaffner 2016). These releases concerned the Asian ladybugs Chilocorus circumdatus (Gyllenhall, 1808) and Chilocorus hauseri Weise, 1895 whose impacts and establishment are unknown, as well as the import of representatives of the genus Aphytis Howard, 1900 (Wood 1963). Although alien Aphelinidae seemed to offer at least partial control of their associated pests, range expansion of Aphytis melinus DeBach, 1959 and A. coheni led to the competitive exclusion of native-to-Cyprus Aphytis chrysomphali (Mercet, 1912) (Orphanides 1984). Ichneumon and braconid releases during the 1960s were aimed at controlling populations of Phthorimaea operculella (Gerber and Schaffner 2016). Most species established viable populations on the island although their efficacy as biological control agents remains unknown (Gerber and Schaffner 2016).

Releases during the 1980s included that of Comperiella bifasciata Howard, 1906 against the citrus pest Aonidiella aurantii (Orphanides 1996), as well as the African species Metaphycus helvolus (Compere, 1926) and Metaphycus lounsburyi (Howard, 1898) successfully combating the olive grove pest Saissetia oleae (Orphanides 1993). In the 1990s, four additional chalcid wasps were recruited against the citrus leaf miner Phyllocnistis citrella Stainton, 1856 (Schauff et al. 1998), although their overall impact is rather unknown (Gerber and Schaffner 2016). The reported intentions of rearing and release of the Neotropical chalcid wasp Cales noacki Howard, 1907 against Aleurothrixus floccosus (Maskell, 1896) have been confirmed (EPPO 1997; Nicos Seraphides pers. comm.). Since the beginning of the 21^st century, no data on intentional releases of alien biological control agents were found. Although this may show that alien insects have not been imported to the island during the last two decades, the presented data (Fig. 5) may also indicate the lack of published information in scientific journals.

The history of biological control agents in Cyprus is largely intertwined with commercial potato, olive and citrus crops. Most of the intentionally introduced species have successfully established on the island (81%). However, the efficacy of these releases remains unknown for the vast majority of species (71%). Out of the 19 alien species introduced against citrus pests, only four were reported to offer some degree of control over their hosts (Gerber and Schaffner 2016). Regarding potato crops, out of the ten alien biological control agents introduced to the island, only Apanteles subandinus was reported to effectively tackle the common and destructive potato moth Ph. operculella (Greathead 1976; Georghiou 1977; Gerber and Schaffner 2016). The inaccessibility of data may be the reason why the percentage of biological control agents considered to be successful in controlling the pest, against which they were released, is seemingly low. For example, in contrast to the only data made available online, stating the intentions of introducing and rearing C. noacki (EPPO 1997), the species has not only been introduced and released, but it is also well-established and has provided successful control of A. floccosus (Nicos Seraphides pers. comm.).

It could be informative to map the current distribution of historically-known introduced biological control agents to the island, such as Aphelinus mali (Haldeman, 1851) or Copidosoma koehleri Blanchard, 1940, species for which the presence of established populations is currently unknown (Gerber and Schaffner 2016). The presence, efficacy and non-target effects of biological control agents would be valuable for assessing the benefits of these species, while documenting overall impact towards native biodiversity.

Positive impacts of alien insects are largely anecdotal. Out of the 37 species identified, less than half (41%) concerned intentional introductions of biological control agents, as the efficacy of most intentionally introduced species remains unknown. The remaining insects, unintentionally introduced along with their host-plants, reduce the growth of alien invasive plants, such as that of Leucaena leucocephala (Lam.) de Wit by its obligate seed-feeding beetle Acanthoscelides macrophthalmus (Schaeffer, 1907) (Vassiliou and Papadoulis 2008) or Ficus microcarpa L. suppressed by alien non-pollinating fig wasps that inhibit its seed-germination and subsequent spread (Demetriou et al. in press). Although the 37 insect species with registered positive impacts may be presumed as beneficial, the overall lack of studies assessing their integration into natural ecosystems and food-chains may bias such conclusions.

Studies addressing the adverse impacts of alien insects in Cyprus mostly focus on insects of agricultural or horticultural significance (Morris 1937; Georghiou 1977; Kontodimas et al. 2006; Şişman and Ülgentürk 2010; Ülgentürk et al. 2015; Compton et al. 2020b; Hadjiconstantis and Zoumides 2021). The impacts of alien insects on the biodiversity of Cyprus has received minimal attention, evidenced by the small number of alien insects (19 species) classified as invasive (Fig. 6). These species include, inter alia, the rosemary beetle Chrysolina americana infesting native aromatic plants (Hadjiconstantis and Zoumides 2021), the aphid Myzus persicae Sulzer, 1776 (Georghiou 1977; Ioannou and Iordanou 1987), as well as two scale insects Aspidiotus nerii Bouché, 1833 and S. oleae feeding on native and alien plants (Morris 1937; Georghiou 1977; Orphanides 1993; Şişman and Ülgentürk 2010; Compton et al. 2020b). In addition, four hymenopterans are known to compete with and displace native species (Orphanides 1984; Salata et al. 2019), while another has been found parasitising a native scale insect (Georghiou 1977). Lastly, two alien Siphonaptera, Ctenocephalides canis (Curtis, 1826) and Ctenocephalides felis (Bouche, 1835) have been found to negatively affect human and animal health as vectors of pathogens (Psaroulaki et al. 2006, 2014) (Suppl. material 2).

The impacts of alien insects in Cyprus are unquestionably in need of a detailed literature investigation covering both published and unpublished literature. Impact assessments, using the protocols and criteria of EICAT and SEICAT (Hawkins et al. 2015; Bacher et al. 2017; IUCN 2020; Kumschick et al. 2020a), to comprehensively assess the impacts of alien insects of Cyprus would be valuable in providing a list of invasive alien species of national concern. Additionally, such impact assessments could be included within risk assessments and should take into account any recorded impacts of alien insects studied in neighboring Mediterranean and Middle-Eastern countries (e.g. Egypt, Greece, Israel and Turkey). Thus, these assessments could act as an early warning system for insects with harmful impacts detected in neighboring regions (Kumschick et al. 2020b), which have been classified as data-deficient in Cyprus, but also species remaining undetected or yet to have reached the island. Nevertheless, the updated checklist of alien-to-Cyprus insect species (Suppl. material 1) constitutes an important first step towards prioritising management decisions and implementing monitoring schemes for invasive alien species on the island.

Horizon scanning for invasive alien species with the potential to threaten biodiversity, human health and the economy of Cyprus (including insects) have been already implemented, addressing species with high likelihood of arrival, establishment and potential impacts (Peyton et al. 2019, 2020). A total of 14 alien insects likely to be imported and established on the island were prioritized. Amongst them, four alien mosquitoes (Aedes spp.) with the potential to harm human health and well-being, crop-pests, such as Leptinotarsa decemlineata Say, 1824, Daktulosphaira vitifoliae (Fitch, 1855) and Anoplophora spp., but also invasive alien species, such as Linepithema humile (Mayr, 1868) and Vespa velutina Lepeletier, 1836 (Peyton et al. 2019, 2020). These species could be included in alert-lists (Peyton et al. 2019). Management measures could benefit from the construction of dynamic, dichotomous identification keys available online for the rapid identification of species in order to support border control and phytosanitary surveillance. In parallel, data availability, usefulness and transparency could be enhanced by data-digitisation of grey literature, following core biodiversity data standards (Groom et al. 2017). In accordance with these recommendations, the updated checklist and data curated by the ACE database are being integrated to the CyDAS, with hopes that they can assist risk assessments on a national and European level.

Lastly, the large percentage of alien insects assessed as data-deficient (47%) (Fig. 6) combined with the high percentage of species whose establishment status is considered unknown or presence is doubtful (25%) (Fig. 4), clearly illustrate the necessity for “more boots in the ground” (Wilson 2017) regarding the study of insects in Cyprus.