Invasive orchid bee outperforms native bees to promote an invasive Solanum

Little or nothing is known about the potential effects of naturalized solitary or semi-social bees on the environment. Here we took advantage of the recent naturalization of an orchid bee, Euglossa viridissima, in southern Florida to study the effects of this semi-social bee on reproduction of Solanum torvum, an invasive shrub. Flowers of S. torvum have a specialized pollination syndrome called buzz pollination, in which their anthers dehiscent through apical pores and require bees to vibrate out the small pollen grains and to deposit the pollen on stigmas. Through timed floral visitor watches and six pollination treatments: open, open with pollen supplement, single visits from halictid bees, single visits from  E. viridissima, and small and large mesh cages (to deny or allow E. viridissima access, respectively) at two sites we found that the orchid bee outperformed the native bees. The orchid bee is superior in all measures of pollination processes of S. torvum, including the proportion of time in patches, number of visits, number of flowers visited, and pollination efficiency. Moreover, when the orchid bee was excluded, the flowers set 1/4 as many fruits as when the bee was given the access. Where the orchid bee was abundant, its frequent and efficient visits completely eliminated pollen limitation in S. torvum plants. The overall importance of the orchid bee as a pollinator was 96 times higher than that of halictid bees. This specialized invasive mutualism may promote populations of both the orchid bee and this noxious weed.