HORTICULTURAL ENTOMOLOGY Pollination Efficiencies of Three Bee (Hymenoptera: Apoidea) Species Visiting Rabbiteye Blueberry 1 2 BLAIR J. SAMPSON AND JAMES H. CANE J. Econ. Entomol. 93(6): 1726Ð1731 (2000) ABSTRACT Inadequate bee pollination limits rabbiteye blueberry, Vaccinium ashei Reade, pro- duction in the some areas of the southeastern United States. Honey bees, Apis mellifera L., are currently the only manageable pollinators available for pollinating V. ashei. However, a new adaptable pollinator for rabbiteye blueberry, Osmia ribifloris Cockerell, was successfully reared and ßown in captivity. The bee nested successfully in wooden shelters and conferred superior fruit set to 2-yr-old potted, rabbiteye blueberry bushes. Pollination efÞciency or the percentage of blueberry ßowers to set fruit after being visited once by a female O. ribifloris was comparable to that of the female blueberry bee Habropoda laboriosa (F.) and worker honey bees. Interestingly, honey bees once thought to be inefÞcient pollinators of rabbiteye blueberry were found to be very efÞcient, especially for ÔClimaxÕ and ÔPremierÕ ßowers. KEY WORDS Apis mellifera, Habropoda laboriosa, Osmia ribifloris, blueberry, pollination, fruit set BLUEBERRY PRODUCERS HAVE traditionally relied on wild H. laboriosa by active management is difÞcult and bees for blueberry pollination. Many native bee spe- might further be hindered by a tendency of females to cies are highly efÞcient pollinators with single visits to abandon their burrows after disturbances to nesting virgin ßowers setting Ͼ40% fruit (Cane and Payne substrates (Cane 1995). A very promising and new 1990, Payne et al. 1991); repeated or unrestricted visits pollinator for blueberries is a solitary, cavity-nesting can further improve fruit set and size (Danka et al. bee indigenous to the western United States, Osmia 1993, Stubbs and Drummond 1999). For many of the ribifloris Cockerell (Torchio 1990). O. ribifloris co- SoutheastÕs Ϸ10,000 acres of blueberry farmland, pol- coons can be safely harvested and transported and lination problems arise in larger Þelds where there are after a brief courtship period adult females will nest in too few bees to pollinate available blossoms. Clepto- portable wooden shelters. The bee is native to the parasites, pesticides, and competing bloom also con- United States and is subject to less regulation than the tribute to lower pollinator abundance in blueberry A. pilipes and is far easier to manage than H. laboriosa. Þelds (Parker et al. 1987; Payne et al. 1989; Spiers 1990; Osmia ribifloris is a pollen specialist of plants like Torchio 1990; Cane 1993, 1995, 1997; Cane and Payne blueberries that are in the heath family (Ericaceae). 1993; Batra 1995, 1997; Kevan et al. 1997; Pittman et al. Although the single-visit pollination efÞciency of O. 1998). ribifloris females at blueberry ßowers has not been The long-tongued bees Anthophora pilipes Smith determined, when bees were given unlimited and sole (Anthophoridae), Habropoda laboriosa (F.) (An- access to ßowers of rabbiteye blueberry, Vaccinium thophoridae), and Osmia ribifloris Cockerell ashei Reade, average fruit set was 54% (Sampson et al. (Megachilidae) have been evaluated as supplemental 1995). Also, adult emergence, courtship, foraging and pollinators of the major North American blueberry oviposition for this bee can be timed to coincide ex- crops (Cane and Payne 1990, Torchio 1990, Batra 1994, actly with rabbiteye blueberry ßowering. Adult O. Stubbs et al. 1994, Cane 1997, Stubbs and Drummond ribifloris live Ϸ2Ð3 wk (Torchio 1990, Stubbs et al. 1999). A. pilipes nests in portable clods of adobe clay 1994) and their offspring overwinter as preemergent and pollinated both highbush and lowbush blueber- adults in silken cocoons. Thus, there is no need to feed ries (Batra 1994, 1997; Stubbs and Drummond 1999). O. ribifloris beyond blueberry bloom (Parker et al. Originally from Japan, A. pilipes is currently in quar- 1987). antine and unavailable to blueberry producers To justify releasing O. ribifloris into southern blue- (Stubbs and Drummond 1999). H. laboriosa is a wild berry orchards, the beeÕs relative pollination efÞ- and efÞcient native bee pollinator that, although spe- ciency must Þrst be compared with already estab- cializing on southern blueberries, is often rare in many lished and important blueberry pollinators. The two commercial blueberry Þelds. Bolstering populations of important southern pollinators are the native H. la- boriosa, and European honey bee, Apis mellifera L. 1 Small Fruit Research Station, USDA-ARS, Poplarville, MS 39470. The percentage of fruits set after single visits by bees 2 Bee Biology and Systematics Laboratory, USDA-ARS, Utah State to virgin rabbiteye blueberry ßowers is a useful and University, Logan, UT 84322Ð5310. standardized measure of pollination efÞciency (Cane December 2000 SAMPSON AND CANE:POLLINATION EFFICIENCIES OF THREE BEE SPECIES 1727 1997). Xenia pollen effects in blueberry fruit set (Gup- O. ribifloris subspecies between the years 1999 and ton 1984, 1997) should not seriously affect compari- 2000. All females were released during blueberry sons of single-visit pollination efÞciency for this and bloom. We also obtained 565 males, of which one-third other studies, because the interplanting of only a few were released in the screenhouse for mating purposes. highly compatible V. ashei cultivars is consistent Nectar and pollen for the bees was supplied by nearly throughout the Southeast. The three most common equal proportions of 2-yr-old ÔClimaxÕ, ÔPremierÕ, and cultivars ÔTifblueÕ, ÔPremierÕ, and ÔClimaxÕ are largely ÔTifblueÕ plants (n ϭ 300 plants). Portable nesting self-incompatible and currently comprise 80% of the shelters each housed 17 acrylic-coated, untreated pine rabbiteye blueberry production in the southeastern blocks. Each block provided female O. ribifloris with United States (Spiers 1990). Þve or 10 tubular nests lined with paper straws (0.7 cm diameter by 15.0 cm long). Potted strawberry, rose, oak, and southern highbush blueberry plants supplied Materials and Methods female O. ribifloris with suitable leaf material to fash- Fruit set resulting from single visits by bees to 887 ion nest cell partitions and entrance plugs. Additional ßowers occurred on potted, 2-yr-old ßowering V. ashei nest shelters and blocks were provided as needed. plants from the commercial cultivars Climax, Premier, Tanglefoot barriers (Tanglefoot, Grand Rapids, MI) and Tifblue. Single-visit fruit set is a standardized prevented predation of bee brood by the red imported measure of pollination efÞciency that is independent Þre ant, Solenopsis invicta Buren. Single visits by O. of pollinator foraging density. Plants were exposed to ribifloris occurred at 348 virgin ßowers from a total of the same environmental conditions and handling to 134 racemes from 15 plants per cultivar. ensure that management practices did not contribute The second study site was at two nearby rabbiteye to differences in fruit set. Only virgin ßowers on plants blueberry plots (USDA-ARS Small Fruit Research Sta- received single visits by bees; plants were left in the tion in Poplarville, MS). The plots contained Ϸ200 Þeld for only a few hours each day and then returned blueberry plants ranging from 2 to 15 yr of age, hosted to a common area (screenhouse) to mature fruit. All a large foraging population of H. laboriosa, and pro- potted plants received the same amount of water and vided highly compatible pollen sources (ÔClimaxÕ, fertilizing. Intraclonal variability was reduced by se- ÔPremierÕ, ÔTifblueÕ, ÔWoodardÕ, and ÔDeliteÕ). We ob- lecting plants of the same age, plants growing in the served single visits to 434 ßowers by H. laboriosa at 72 same type and size of pot, same soil medium and from racemes from six plants, two plants for each cultivar. the same mother plants and nursery. Plants were returned to a screenhouse so they could On 36 racemes, 228 virgin ßowers were enclosed in mature fruit under the same conditions as plants used Þnely woven mesh bags to completely exclude polli- to evaluate captive O. ribifloris already conÞned inside nators (unvisited control). Caging plants within the screenhouse as well as plants visited by honey bees 1.5-m3 Lumite enclosures (Synthetic Industries, from another site. Gainesville, GA) greatly increased the number of vir- The third and most remote site in 1999 was a com- gin ßowers that were available to bees. Any open mercial blueberry farm, 100 km SE of the Poplarville ßowers that could have been previously visited by an station. No screenhouse existed at this site; O. ribifloris insect pollinator were removed before caging. were not released and Habropoda were entirely ab- When sufÞcient ßowers had opened, random plants sent. This provided a unique opportunity to test the were brought to each of three study sites. Bags or cages pollination efÞciency of honey bees without native were then removed to expose virgin ßowers to single blueberry pollinators being present, a situation that pollination visits by both nectar and pollen foraging normally necessitates the renting of honey bee colo- female bees. Male bees rarely visited our virgin ßowers nies for blueberry pollination. Commercial honey bee and so were not included in the data analysis. colonies were clustered along the tree line at a stock- The Þrst study site was inside a 133-m2 screenhouse ing rate of 1.2 colonies per acre. Compatible pollen at the USDA-ARS Small Fruit Research Station, Pop- sources at the third site included