Diversity and Pollen Loads of Flower Flies (Diptera: Syrphidae) in Cranberry Crops

Abstract

Flower flies are one of the most important groups of pollinators worldwide. Unfortunately, little is known about their pollination capacity and the importance of their role for many crops grown commercially, such as cranberries. To address this information gap, 12 cranberry farms were sampled during the blooming periods of 2013 and 2014 in Quebec, Canada, to evaluate hoverfly diversity and pollen load. Moreover, the effects of the following three factors on community structure were investigated: farm management (organic vs conventional), edge mowing (mowed vs non-mowed), and type of adjacent natural habitat (forest vs meadow vs bog). Flower flies were captured using pan-traps and hand-netting once a week for 3 wk. In total 461 specimens of flower flies were captured and 33 species were identified. Among the three factors studied, edge mowing explained most of the variation among communities, followed by farm management. Natural habitat type did not appear to influence hoverfly communities, contrary to our expectations and reports from other studies. Pollen load analyses and interactive connectance plot showed that two flower fly species, Syrphus torvus Osten Sacken and Eristalis tenax L. (Diptera: Syrphidae), transported the most cranberry pollen, both in terms of quantity and proportion.To our knowledge, this study is the first to describe and provide a complete list of flower fly species found in cranberry crops. Our results also highlight the importance of floral resource diversity for these potential cranberry pollinators, since edge mowing was revealed to be the most influential of all factors we considered.