Evaluating hornfaced bees (Osmia cornifrons Radoszkowski) as pollinators of highbush blueberry

The highbush blueberry (V. australe Small and V. corymbosum L.) is the major cultivated species of blueberry in North America. A good commercial blueberry crop requires that at least 80 percent of the blossoms set fruit. Blueberry flowers are characterized as being an entomophilous flower, which is defined as a flower adapted for insect pollination. Three types of bees account for nearly all of the pollination of blueberry flowers; bumblebees (Bombus spp.), honeybees (Apis mellifera L.) and solitary bees (Osmia spp.). Due to cost and maintenance issues of honey bee colonies, other pollinator species for blueberry pollination needs to be evaluated.

Four pollinator treatments were evaluated; hornedfaced bee (Osmia cornifrons Radoszkowski), honey bees, natural pollinators, and no pollinators to determine if use of the hornedfaced bee will successfully pollinate blueberry blooms and produce an increased fruit set and a higher quality berry as compared to the other pollinator treatments. Hornfaced bees were not significantly different with respect to berry number, berry weight and weight per berry from the commercial bumble bee and the honey bee. The key difference was the population numbers of each treatment. Hornfaced bees per tent were approximately 30, commercial bumble bees per tent were approximately 75 and the honey bees per tent were approximately 10,000. This Preliminary data suggests that hornfaced bees are as or more efficient than other tested pollinators in this project.

Introduction:

Ericaceae are mostly shrubs comprising about 125 genera and 3,500 species which include several members that have economic importance for ornamentals and edibles in the U.S. Ornamental members include the genus Rhododendron (azalea and rhododendron) and edible members include the genus Vaccinium (cranberry and blueberry). Blueberry plants are cultivated primarily for their berries which can be eaten fresh or processed. Blueberry consumption has an added health benefit which has increased their market demand. Researchers at the USDA Human Nutrition Center (HNRCA) have found that blueberries have the highest antioxidant activity when compared to 40 other fresh fruits and vegetables (Wang et al., 1996). Antioxidants help neutralize harmful by-products of metabolism called "free radicals" that can lead to cancer and other age related diseases (Prior et al., 1998). Anthocyanin, a plant pigment that makes the blueberries blue is thought to be responsible for this major health benefit. Three distinct types of blueberry: rabbiteye (V. ashei Reade), lowbush (V. angustifolium Ait. and V. myrtilloides Michx.) and highbush (V. australe Small and V. corymbosum L.).

The highbush blueberry is the major cultivated species of blueberry in North America (NRAES, 1992). A good commercial blueberry crop requires that at least 80 percent of the blossoms set fruit (Merrill, 1936). Blueberry flowers are characterized as being an entomophilous flower, which is defined as a flower adapted for insect pollination and includes traits such as fragrant, pollen that is not wind-borne, and nectar producing (Eck, 1988). An entomophilous flower discourages self-pollination and encourages cross-pollination.

Three types of bees account for nearly all of the pollination of blueberry flowers; bumblebees (Bombus spp.), honeybees (Apis mellifera L.) and solitary bees (Osmia spp.)(Eck, 1988). Eck (1988) states that bumblebees are excellent pollinators but are not very prevalent during blueberry bloom and where land is intensively cultivated and suggests that colonies of honeybees are essential to insure adequate blossom pollination. Native bees have shown to interfere with blueberry pollination including a species of bumblebee (Bombus occidentalis Greene) and a species of carpenter bee (Xylocopa virinica L.)(Maloof, 2001; Sampson et al., 2004). Both of these species will cut slits at the base of the flower to reach the nectar, bypassing flower reproductive parts, thus they do not assist in pollination and has been termed as nectar robbery. Nectar robbery can have significant effects on reducing pollination of blueberry flowers due to the overlapping of foraging times of honeybees and carpenter bees. Sampson et al (2004) states that honeybee workers do not actively gather blueberry pollen and have a stronger predilection for gleaning nectar from robbery slits reducing their effectiveness as pollinators. Solitary bees are often considered to be pollen bees. Pollen bees gather pollen and honey to make bee bread used to feed their brood. Solitary female bees will mate, makes a nest with about 10 brood cells, stocks each cell with a nectar and pollen mixture as food for her larvae, lays an egg in each, and dies before her young emerge (Batra, 1994). Batra (1994) states that approximately 85% of all bees are pollen bees but due to intensive and extensive cultivation, urbanization and pesticide use, natural populations have declined in many areas resulting in the need for introduced colonies of honeybees for successful pollination.

The first species of pollen bee to be brought into management was the hornedfaced bee (Osmia cornifrons Radoszkowski) which was introduced in the U.S. from Japan in 1977 (Batra, 1994). Batra (1994) gives 10 reasons for the rapidly increasing popularity of hornfaced bees and their close relatives for pollination which are: 1. these bees are active in the spring, before honeybee colonies reach large sizes; 2. they prefer fruit flowers, thus stay in the crop; 3. they usually contact the flowers’ anthers and stigmas on every visit; 4. they fly rapidly, thus working many flowers; 5. the pollen is carried loosely under the abdomen, thus being freely dusted on the stigmas; 6. males also pollinate; 7. their short flight range keeps them in the orchard; 8. growers can easily raise their own bees; 9. they are gentle, with a mild sting; and 10. they can be stored away between pollination seasons. Another important aspect of the hornedfaced bee is that as few as 80 female bees are needed per hectare of apples which contrast with the thousands of bees recommended per hectare for pollination of an orchard (Batra, 1994). Mites and diseases that trouble honey bees do don infest hornedfaced bees and they cannot interbreed with Africanized "killer" honeybees. Research has been conducted on different plant spp. (Brassica spp., Sinapis alba, Helianthus petiolaris) comparing the horned faced bee with honeybees to determine pollination efficacy within controlled field cages (Abel et al., 2003; Wilson et al. 2000). Wilson et al. (1999) stated that using honeybees as compared to hornedfaced bees in field-cage pollinations of Brassicaceae, there was a seven-fold cost increase making the hornedfaced bees more economical for use as a crop pollinator.

Literature Cited

Batra, S. 1994. Diversify with pollen bees. Amer. Bee J. 134(9):591-594.

Eck, P. 1988. Blueberry Science. Rutgers University Press. New Brunswick, NJ

Maloof, J.E. 2001. The effects of a bumble nectar robber on plant reproductive success and pollinator behavior. Amer. J. of Bot. 88(11):1960-1965.

Merrill, T.A. 1936. Pollination of the highbush blueberry. Mich. Agr. Expt. Sta. Tech. Bul. 151.

Natural Resource, Agriculture, and Engineering Service. NRAES-55. Highbush Blueberry Production Guide. 1992.

Prior, R.L., G. Cao, A. Martin, E. Sofic, J. McEwen, C. O’Brien, N. Lischner, M. Ehlenfeldt, W. Kalt, G. Krewer, and C.m. Mainland. (1998). Antioxidant Capacity As Influenced by Total Phenolic and Anthocyanin Content, Maturity, and Variety of Vaccinium Species. J. Agric. Food Chem.46(7):2686 - 2693.

Sampson, B.J., R.G. Danka, and S.J. Stringer. 2004. Nectar robbery by bees Xylocopa virginica and Apis mellifera contributes to the pollination of rabbiteye blueberry. J. Econ. Entomol. 97(3):735-740.

Sanford, M. 1998. Pollination, the Forgotten Agricultural Input. Proceedings of the Florida Agricultural Conference and Trade Show J. Ferguson, et al eds., pp. 45-47

Wang, H., Cao, G. and Prior, R.L. (1996) Total antioxidant capacity of fruits. J. Agric. Food Chem. 44:701-705.

Wilson, R.L., C.A. Abel and R.L. Luhman, 1999. Comparing three bee species for controlled pollination of selected Brassicaceae. J. Iowa Acad. Sci. 106:1-3.