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).