Bees perform a vital ecosystem function as the dominant insect pollinators in both agricultural and natural ecosystems (Klein et al. 2007). Native and managed bees pollinate crops, such as nuts (almonds, pistachio), fruits (raspberry, blueberry, tomato), fiber (cotton), and forage (alfalfa seed). It has been estimated that one-third of the world’s crop production is made possible by insect pollination, the majority of it coming from bees, and insect pollination contributes an estimated $27 billion to the U.S. economy and $210 billion worldwide (Calderone 2012; Gallai et al. 2009; Klein et al. 2007). Western honey bees (Apis mellifera Linnaeus) are the most widely used managed pollinators, yet studies show that a diversity of other bees contribute to improved crop quality and yield (Garibaldi et al. 2016). For example, the blue orchard bee (Osmia lignaria Say) is a native, solitary bee that nests in pre-existing cavities and has been used as an alternative to and as an enhancement for honey bees in orchard pollination in the U.S. and Canada (Torchio 1976; Bosch and Kemp 2002). Pollination services provided by O. lignaria have resulted in a two-fold increase in sweet cherry yield (Bosch et al. 2006) and increased strawberry size and growth rates (Horth and Campbell 2017).
Over 20,000 species of bees have been identified around the world, but it has been estimated that up to 30,000 species exist worldwide (Michener 2007). Unfortunately, bee populations and the number of species are declining, with potentially devastating consequences to natural and agricultural ecosystems (Biesmeijer et al. 2006; Goulson et al. 2008; Cameron et al. 2011). It is likely that multiple factors are involved in bee declines, including loss of habitat and reduced natural forage, unsustainable management practices, pesticide exposure, and parasites and pathogens (Kearns et al. 1998). Further, the introduction of non-native species, including non-native bees, can have serious economic and ecological impacts (Pimentel 2002; Goulson 2003; Thorp 2003; Pimental et al. 2005; Velthuis & van Doorn 2006).
Although some exotic bees may have positive economic and environmental impacts, such as agricultural pollination, they can also compete with native bees for shared flower resources and nesting sites, increase parasitism and disease transmission rates among native bees, modify the resident plant-pollinator community, and enhance non-native plant spread, leading to additional pressure on ecosystems and their services (Cane and Tepedino 2016; Russo 2016, and references both therein). Forty-six species of exotic bees have already become established in the U.S. (Ascher 2001; Cane 2003; Sheffield et al. 2011; Russo 2016), most of them the result of accidental introductions, and some have shown rapid range expansion beyond their point of introduction (Hinojosa-Díaz et al. 2005; Hinojosa-Díaz 2008; Gibbs and Sheffield 2009; Strange et al. 2011). Taxonomically, half of these exotics belong to the family Megachilidae, which also includes currently managed and potential crop pollinators (Giles and Ascher 2006; Sheffield et al. 2010). Given such introductions, as well as the potential population declines in many native species (Sarospataki et al. 2005; Steffan-Dewenter et al. 2005; Williams 2005) and in particular native pollinators around the globe and in the U.S. (Kearns et al. 1998; Cameron et al. 2011), detection and interception of exotic bees is essential for the preservation of our native pollinators and associated ecosystems.