Native Bees and Pollen Collection: How Flexible Are They?

Abstract

Aim: Globally, populations of the honey bee (Apis mellifera) are declining, threatening pollination services and thus the reproduction of crops and wild plants. Native bees may be a free source of pollination services and act as ‘insurance’ against potential honey bee losses in Australia. This study aims is to determine whether native bees collect pollen mainly from native plants, with which they have a shared evolutionary history, or whether they have diversified and also collect pollen from introduced plant species. To this end, we investigated whether native bees collected more or less pollen from native plants or introduced species, and whether there are differences in the patterns of pollen collection between the different bee genera studied. Methods: This study collected different species of native bees off flowering plants from agricultural and remnant forest sites in the Yarra Valley, Victoria. Pollen was transferred from the bees and taken through acetolysis before being mounted on microscope slides. With the assistance of the Specicount tool, pollen on these slides was identified and counted using a microscope to determine what pollen the bees carried. Pollen loads and pollen load composition were calculated based on this analysis. Results: Rather than all bees collected carrying pollen, for the most part only those with visible pollen on the bee at the time of collection or processing ended up with enough pollen on the microscope slide to analyse. The different taxa of native bees had statistically different pollen load compositions in both the agricultural and forest sites. There was also a correlation between bee body size and the overall amount of pollen carried. All the bees studied carried pollen from both native and non-native plant sources to some extent, ranging from 27% non-native pollen in Exonuera to 78% in Homalictus. When the data set was divided into agricultural sites, different trends emerged, with bees more likely to collect pollen from crops and weeds in agricultural sites. Site type was found as the primary driver of inter-species pollen load composition variation. Main Conclusions: The finding that mostly only bees with visible pollen at the time of collection resulted in visible pollen on the slide will inform the processing of the remaining bee samples in subsequent studies. The pollen load composition of the native bees in this study is not limited to native plants. Location, rather than plant origin, determined the makeup of the pollen load carried by the bees. The native bees in the study have potential as crop pollinators as given the opportunity they will collect pollen from introduced species including crops. Show more