Biotic and abiotic factors contribute to cranberry pollination

Abstract

As bee populations continue to decline, farmers face possible crop failures due to insufficient pollination. Crops, however, vary in the degree to which they depend on pollinators, suggesting that some crops may not be as sensitive to variation in pollinator availability and/or abundance as others. The objective of this study was to determine the contribution of biotic and abiotic factors to cranberry pollination. We performed field and greenhouse experiments to compare the effect of biotic (i.e., bee or hand pollination) and abiotic (i.e., wind, agitation) factors on yield. We found that even in the absence of bees, cranberry is able to produce a significant yield. In the field, plants in the abiotic treatments produced higher yields (wind 230 bbl/ac [barrels per acre], agitation 200 bbl/ac) than the closed control treatment (108 bbl/ac), although these yields were not as high as the open, biotic treatment (367 bbl/ac). This corresponds to a contribution of 41% by bees, 30% by non-bee insects, and 29% by mechanical agitation. In the greenhouse, the agitation treatment had, on average, higher berry weight per upright (0.6 g/upright) than the undisturbed control treatment (0.04 g/upright), but again, not as high as the biotic treatment (3.0 g/upright). This confirmed that cranberry does not autogamously self-pollinate indicating that all yields are due to biotic or abiotic vectors moving pollen between flowers. Although bees clearly contribute to cranberry pollination, previous studies have understated the contribution of alternative mechanisms by which cranberry pollen can move between flowers.