Can small wild pollinators be used practically for fruit set in apple trees?

Abstract

The pollination services provided by small wild pollinators in apple orchards were investigated in Akita Prefecture, northern Japan. In the apple orchard in 2017 and 2018, wild species constituted about 43% of all pollinators collected; these wild pollinators belonged to the order Hymenoptera (with most in the families Andrenidae [Andrena spp.] and Halictidae [Lasioglossum spp.]) and the order Diptera (mainly Melanostoma spp.). To exclude the introduced bees Apis mellifera and Osmia cornifrons, we protected flower bud clusters with 3.5-mm-mesh net bags that allowed access only to small wild pollinators from 2019 to 2021. There was no significant difference between protected and unprotected king flowers in terms of fruit set or the number of ventricles with seeds in the king fruits. Moreover, significantly fewer lateral fruits, which need to be removed by thinning, set in the protected clusters. These observations indicated that apple fruits might set normally without the need for introduced pollinators, and in some cases introduced bees might promote fruiting beyond the capacity of labor to manage.