The domesticated cranberry is a low, perennial woody vine native to northeastern North America (Eck, 1986). Fruit set and fruit size are maximized when eight or more pollen grains are transferred to the stigma of the flower; if fewer than four viable grains reach the stigma, fruits are small, deformed, or altogether absent (Cane and Schiffhauer, 2003). As a result of limited self-compatibility, for optimal fruit set, cranberry requires outcrossing by insect pollinators (Sarracino and Vorsa, 1991). In North America, Apis mellifera, the European honeybee, is used extensively to provide pollination services for cranberry (Evans and Spivak, 2006; Ratti et al., 2008; personal observation). However, cranberry flowers have poricidal anthers whose pollen is best accessed by buzz pollination (Buchmann, 1983; Free, 1993). Because honeybees do not buzz-pollinate, they are considered to be less effective at removing pollen from this type of anther (Cane et al., 1996; Cane and Schiffhauer, 2001; King and Buchmann, 2003; MacKenzie, 1994), although some pollen transfer may still occur while foraging for pollen and/or nectar. Additionally, the number of available hives has decreased with recent threats to honeybee health such as Colony Collapse Disorder. As a result of these factors, alternative pollinators are needed for pollination services in cranberries.
Cranberry pollination research in North America has largely been conducted in the Great Lakes and New England areas and has focused on the use of commercially available bee species: honeybees, managed bumble bees (Bombus spp.; Cane and Schiffhauer, 2003; Evans and Spivak, 2006; Stubbs and Drummond, 1997), leafcutter bees (Megachile spp; Cane et al., 1996; Cane and Schiffhauer, 2003; MacKenzie and Javorek, 1997; Stubbs and Drummond, 1997), and mason bees (Osmia spp.; Cane and Schiffhauer, 2003; Stubbs and Drummond, 1997). In these studies, bumble bees proved to be effective pollinators of cranberries, depositing, on average, over 60 pollen grains per visit, resulting in a twofold increase in berry mass, compared with pollination by honeybees, which deposited only 10 pollen grains per visit (Cane and Schiffhauer, 2003). In addition, honeybees are reported to be more likely than bumble bees to collect nectar and not pollen (MacKenzie, 1994). Although this behavior results in stigmatic contact, pollen foraging yields 63% more berries than nectar foraging (Cane and Schiffhauer, 2001). For these reasons, previous studies have concluded that bumble bees are superior pollinators of cranberry (Cane and Schiffhauer, 2003; Macfarlane, 1995; Ratti et al., 2008), particularly short-tongued bumble bees (Macfarlane et al., 1994; Macfarlane and Patten, 1997). However, others question if populations are sufficient to provide adequate pollination (Evans and Spivak, 2006; Filmer and Doehlert, 1959; Free, 1993). In contrast to the Midwest and the East, little research has been done on cranberry production systems in the west, where ≈16% of the cranberries in North America are produced (BC Cranberry Growers Association, 2007; USDA, 2009a). Of these, Oregon produces 4%, worth $36.6 million (USDA, 2009b).
Cranberries bloom from mid-May to mid-July in Oregon, during which time cool, overcast, and windy conditions prevail. These conditions do not favor foraging by honeybees and can dramatically reduce their pollination efficacy (Burrill and Dietz, 1981; Percival, 1947). In contrast, native bees, adapted to coastal conditions, have the potential to be superior pollinators. There is a great diversity of bees native to Oregon, but little data exist pertaining to which species are present in cranberry-producing areas and which species are associated with cranberry bloom.
The objectives of this study were to: 1) estimate native bee richness and abundance in the cranberry-growing region of Oregon; 2) correlate bee foraging behaviors with the abiotic factors of temperature and wind; and 3) compare pollen loads from honeybees and native bees foraging on cranberry flowers.
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