Bee hotels: a springboard for the invasion of exotic bees
In the meantime, scientific knowledge has also progressed regarding the status of wild solitary bees. National research campaigns and conservation plans have been launched in many countries such as in the United States, England, France and Germany (Drossart & Gérard 2020; Schatz et al. 2021). Citizens’ science programs have also been developed, inviting many civilians to contribute to awareness on solitary bees (Deguines et al. 2018; Koffler et al. 2021). To a certain extent, the increase information on the importance of wild bees and the growing number of evidence on competitive interactions exerted by honeybees on wild bees, may have opened new avenues for other managing practices in favor of wild bees such as the establishment of bees hotels (MacIvor & Packer 2015; von Königslöw et al. 2019). Historically, bee hotels were mainly used as trap nests to sample wild bees or as a tool to improve pollination service to crops (Daineseet al. 2018). Now, the purpose behind this practice is to provide aboveground nesting bees (mostly Xylocopinae and Megachilidae) with nesting substrates that can be locally limiting and therefore help to support their populations. The use of trap nests as bee hotels has also become widely popular (MacIvor & Packer 2015) and they are nowadays commonly sold in garden centres and on online platforms with, for example, more than 1,000 offers listed on Amazon at a price up to 300 US$ (von Königslöw et al. 2019).
However, the multiplication of bee hotels could also be an ecologically unsound practice because they can shelter invasive alien bee species, thereby potentially facilitating their spread (MacIvor & Packer 2015; Geslin et al. 2020; Straffon-Díaz et al. 2021). This second misplaced management is highly problematic, as invasive alien insects can have severe consequences for ecosystems and the economy (Bradshaw et al. 2016). A convincing example involving bees is the case of Bombus terrestris, which has become invasive worldwide (Aizen et al. 2020). The commercial introduction ofB. terrestris nest boxes for pollination services in greenhouses has had dramatic consequences for native wild bumblebee populations in Japan, South America, New Zealand and Australia (Geslin et al.2017). Introduced exotic bumblebees have escaped and robbed flowering resources, thereby disrupting the native bumblebee populations and the structure of plant-pollinator networks (Geslin et al. 2017). More worryingly, exotic bumblebees have brought several pathogens and parasites that have infected native bees (Graystock et al. 2013). Hence, in Argentina, the rapid local extinction of the endemic bumblebeeB. dalhbomii has been associated with the spread of B. terrestris , most likely due to pathogen spillover (Aizen et al.2020).
To date, 80 bee species have been recorded outside of their native range and even though not all are invasive their impact on native ecosystems may be important (Russo et al. 2021). For example,Megachile sculpturalis , a bee native to Asia and accidentally introduced in North America and Europe, has been shown to exhibit aggressive behaviour toward the local bee fauna through nest eviction and competition (Geslin et al. 2020). This species commonly nests in bee hotels whose can, in turn, favour its spread (MacIvor & Packer 2015; Le Féon et al. 2018; Geslin et al. 2020). Recently, Straffon-Díaz et al. (2021) showed that M. sculpturaliscolonized the tunnels of native Osmia spp. in insect hotels while blocking the entrance of their nests. They also showed that M. sculpturalis ’ brood could be infested by local parasites without reducing drastically its reproductive success potentially suggesting apparent competition with native bees through increase in the abundance of parasites for native species. Finally, because most of wild solitary bees (~70-75%; Michener 2007) nest in the ground, bee hotels are susceptible to host less than 15% of all bee species (Rahimiet al. 2021). Overall, we argue that the installation of bee hotels is a misplaced conservation practice because of a) the misinformation of public: evidence showing the capacity of bee hotels to support cavity nesting bee populations is weak (Rahimi et al.2021); b) the misallocation of resources: instead of adding artificial nests, we suggest to conserve natural habitat susceptible to shelter native population of bees, including below-ground nesting bees and c) potential indirect impacts on biodiversity: bee hotels could promote the spread of invasive species with repercussions on native flora and fauna (Ivanov & Fateryga 2019; Geslin et al. 2020).