Bumble Bee Pollinators in Red Clover Seed Production

Abstract

Bumble bees pollinate red clover (Trifolium pratense L.) but impact on seed production depends on the species, abundance, and synchrony with bloom. The objectives of the current study were to examine pollination by a native bumble bee, Bombus vosnesenskii (Radoszkowski), determine the bumble bee fauna associated with red clover in Oregon, and assess if seed set is limiting. In a cage study, yields with B. vosnesenskii (average = 661 kg ha−1) and honey bees (Apis mellifera L.) (average = 640 kgha−1) were comparable. Yields were lower compared with open pollinated plots (average = 1127 kg ha−1), which was likely due to cage effect, as seed set (# seeds/# florets per seed head) was similar in all three treatments (excluding control). Examination of the diversity of endemic bumble bees through field counts and trapping in red clover fields indicated the presence of six species. Over 92% of these were B. vosnesenskii indicating that it is the key pollinator in Oregon. Seed set across four commercial fields was high (0.84–0.88) documenting that existing pollinators, including rented honey bees, and indigenous bumble bees and solitary bees, provide close to maximum pollination of red clover in Oregon. Higher yields will require improved production practices and new cultivars with more heads per plant. Sustainability of high yields in Oregon will depend on protection of indigenous bee pollinators through conservation of habitats that provide nesting sites, judicious pesticide use, and provision of floral resources before red clover bloom.

When ecosystem services interact: crop pollination benefits depend on the level of pest control

“…The effect on red clover seed set by individually manipulating the supply of the two ecosystem services followed expectations. We observed a considerable increase in seed set following augmentation of insect pollination, which is in line with earlier reports on the importance of insect pollinators for seed set in red clover [19,25]. Maximum average seed set under high levels of pollination and pest control was still under 60 per cent, which may be due to a limited proportion of fertilized ovules setting seed in tetraploid red clover, or partial inability of B. terrestris to successfully pollinate tetraploid red clover flowers [26,27].…”

Investigating Temporal Patterns of a Native Bee Community in a Remnant North American Bunchgrass Prairie using Blue Vane Traps

“…Although originally designed for beetle collection, Stephen and Rao (2005, 2007) discovered that these traps also attract a variety of native bees and have used them in several studies of agroecosystems (Stephen and Rao 2005, 2007; Rao and Stephen 2009, 2010; Stephen et al 2009). This trapping method adds another option for sampling native bees to the traditional methods used that include sweep- and hand-netting, visual observations in plots or along transects, pan traps, and trap nests (reviewed by Westphal et al 2008).…”

Relationships between parasitism, bumblebee foraging behaviour, and pollination service to Trifolium pratense flowers

“…Trifolium pratense (Fabaceae; red clover) is pollinated by a small number of bee species, including bumblebees (Rao & Stephen, 2009), and bumblebee visitation is positively related to seed set (Gillespie & Adler, 2013). Flowers are composed of multiple florets arranged into a single inflorescence head ('flower' from now on).…”