Main doc

Efforts to prevent and manage invasive alien species have been developed globally over the past 30 years (Foxcroft et al. 2017). For most taxa, the rate at which new records are made is increasing over time suggesting that past efforts to curb invasions have been insufficient to cope with increasing globalization (Seebens et al. 2017). The prevailing paradigm for the research, monitoring and management of invasive alien species is that of early detection and rapid response (EDRR, Crall et al. 2012). However, to translate EDRR into an effective operational system, there is an urgent need for regular monitoring activities carried out according to a well-established monitoring plan (Reaser et al. 2020). EDRR would help prevent and reduce the impacts of biological invasions, considered one of the greatest threats to biodiversity, natural ecosystems and human well-being (Early et al. 2016; Blackburn et al. 2017). Invasive alien species are disproportionately prevalent on islands, where they also generate disproportionate impacts compared to continental areas, making them of greatest conservation value (Russell et al. 2017). Because islands tend to have fewer points of entry, they predispose themselves to successful biosecurity.

The impact and distribution of invasive alien species will continue to grow and interact with other global change threats, including climate change. A good proportion of invasive alien species has the potential to become major pests, primarily impact agricultural values, in the new areas unless effective monitoring and management systems are in place (Hellmann et al. 2008). The damage and costs associated with managing established invasive alien species (approximately 40% of global crop production is lost to pests each year, resulting in substantial management expenses of around US$28.17 billion just in Europe) could exceed the costs of measures taken to prevent introductions from occurring (Haubrock et al. 2021; IPPC Secretariat 2021). European states consolidated regulations, such as Regulation (EU) 2016/2031, Regulation (EU) 2021/2285, and Regulation No. 1143/2014, addressing plant health and invasive alien species by establishing a comprehensive framework for prevention, control, and management of such species within the European Union, fostering environmental protection and sustainable agriculture. The regulations derive their foundation from key international conventions such as the International Plant Protection Convention (IPPC) and the Convention on Biological Diversity (CBD), as well as pertinent EU directives including the Habitats Directive (92/43/EEC) and the Birds Directive (2009/147/EC). In this regard, surveillance includes monitoring, assessment and capacity building for detection and diagnosis at all levels, development of an EDRR plan and risk mitigation measures, and a list of pests of quarantine concern at regional and national levels. However, surveillance is often designed on a threat-by-threat basis. As such, it is prone to inefficiency and is often costly and time-consuming. Therefore, there is a strong need for surveillance that takes an integrated view, one that considers several threats/pests simultaneously, and identifies and prioritizes areas for multi-threat surveillance (see Jarrad et al. 2011).

In this study, we developed a surveillance plan that included a list of exotic and invasive insect pests, a trapping network for a total of 20 invasive alien species, and an EDRR system (Table 1). Twelve trapping stations were placed in areas of entry (ports and airport) and distribution of plant material (garden centres; Fig. 1), which were visited every two weeks, approximately, and fresh attractants were deployed following the period suggested by the manufacturer (Table 1). Shortly after implementing it in the Balearic Islands (Westernmost Mediterranean islands), we reported the introduction of a new species not previously detected, demonstrating its effectiveness in preventing and eradicating invasive alien species.

Table 1 List of insect species included in the EDRR system, regulations, type of trap and lure and their trade names. Start date of trapping May 2022
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Fig. 1
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Location of study sites in Mallorca (The Balearic Islands, Westernmost Mediterranean Archipelago). Maps were generated using the get_stamenmap function in the ggmap R package implemented in RStudio (Kahle and Wickham 2013)

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The traps and attractants used are the most specific ones for each target species available on the market. Nevertheless, they also had an effect on non-target insects. For example, we used VelutinaTrap for the detection of V. velutina, which consist in a yellow funnel, green lid and transparent base with a device within the base that prevents captured hornets from coming into contact with the food attractant. Between July and December 2022, a total of 2389 individuals were collected using VelutinaTraps from the twelve regions sampled in Mallorca. In this regard, VelutinaTraps captured: 65.8% Hymenoptera, 24.6% Diptera, 7.2% Coleoptera, 2.1% Lepidoptera, and just 0.3% Hemiptera. The total number of individuals captured was similar between traps placed on ports (P) and near to garden centres, with 1222 and 1066 individuals collected respectively. Finally, 101 individuals were collected at the airport (Fig. 2).

Fig. 2
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Number of captures per trap per day in each study site (P = Ports, GC = Garden Centres and the airport). Abundance patterns and pie chart of main insect orders, indicating the total number of individuals collected during July and December 2022 in VelutinaTraps are provided for each study site. Moreover, we indicate the sampling effort (days of trap deployment) per each site. Finally, red arrows in P4 indicate V. crabro captures

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Vespa velutina, commonly known as the yellow-legged hornet, is one of the species included in our trapping network. It is a polyphagous insect that preys on other insects, posing a significant threat to biodiversity and beekeeping. The first detection of V. velutina in Mallorca was in 2015. The species was officially eradicated in 2020 (Leza et al. 2021), and after two years with no specimens detected, a new introduction was confirmed in 2021. The nest was located and physically removed, and based on genetic analysis all males sampled were determined to be sterile, and a new entry of the yellow-legged hornet in the island (Herrera et al. 2023). Since then, neither nest nor individuals have been detected on the island. This new entry justifies the need to implement effective biosecurity measures to prevent invasive alien species in our study area. Therefore, V. velutina was included in the early detection network operating since July 2022. In VelutinaTrap, a specimen of the European hornet V. crabro was found in the port of Alcúdia (P4) on August 26th, which represents an unexpected finding of a congeneric species of V. velutina. A total of 8 individuals have been collected in VelutinaTrap. This omnivorous eusocial insect preys on various arthropods, including honeybees and it is found in Eurasia (Carpenter and Kojima 1997) and as an alien species in Central and North America (Kimsey and Carpenter 2012), and recently detected in Canada (Bass et al. 2022). Vespa crabro has been previously detected on a Mediterranean island, particularly on Sardinia (Italy) in 2010, and currently invasive surveillance programs concluded that the European hornet does not pose a threat to beekeeping (Pusceddu et al. 2022). Nonetheless, the potential impact on island biodiversity is unknown. It is worth noting that social Hymenoptera appear to be well-suited for dispersal through human transport. The establishment of a new population only needs a single fertilized queen. Moreover, they possess impressive dispersal capabilities, high rates of reproduction, diverse diets and habitats, effective defences against predators, and exceptional competitive skills (Moller 1996). These attributes enhance their capacity to establish, proliferate, and significantly impact native ecosystems once they inhabit a new region (Beggs et al. 2011). For example, there are endemic taxa including 16 wasps, and 9 bees in the Balearic Islands which could be potential prey for the European hornet (Baldock et al. 2020). Following established protocols, we notified ministry in charge of invasive species who responded to the finding as if it were a potentially invasive species and initiated the protocol for nest search. The protocol consists of installing feeding points with protein attractant (raw fish) in the area to identify the direction the hornets take to the nest, same protocol used to find V. velutina nests in Mallorca and described in Leza et al. (2021).

Our paper introduces the inaugural early detection network for invasive insects in the Balearic Islands. This trapping network was designed as species-specific as possible, nonetheless, it has been instrumental in detecting related species of alien species from the same genera, which was later classified as a potentially invasive alien species by the biosecurity authorities. Hence, the surveillance network could exhibit sensitivity to a wider range of alien species.