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Title: Association between density of honey bee (Hymenoptera: Apidae) foragers and fruit set in commercial fields of rabbiteye blueberries in Louisiana and Mississippi

item Danka, Robert
item Sampson, Blair
item Villa, Joseph

Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/21/2018
Publication Date: 2/11/2019
Citation: Danka, R.G., Sampson, B.J., Villa, J.D. 2019. Association between density of honey bee (Hymenoptera: Apidae) foragers and fruit set in commercial fields of rabbiteye blueberries in Louisiana and Mississippi. Journal of Economic Entomology. 112(3):1322-1326.

Interpretive Summary: Rabbiteye blueberries are an import crop grown in the southeastern United States. Good production of the crop requires adequate cross pollination during bloom, a service provided by various types of bees as they forage on the flowers. There is uncertainty about the usefulness of honey bees as pollinators of this crop. We examined the relationship between the density of foragers of four species bees and fruit set in commercial fields of rabbiteye blueberries in Louisiana and Mississippi for three years. Overall, fruit set was good despite the density of foraging bees being highly variable from field to field and from year to year. A strong relationship between foraging activity and fruit set was found in only one of three years. Honey bees were the most abundant pollinator each year. They increased fruit set, but this effect was only strong in the largest fields where other bees were scarce. In one year, supplemental colonies of honey bees were added to fields at different densities (one or five colonies per acre). We did not find increased density of foragers or fruit set in these fields, suggesting that bees found forage sources more attractive than the blueberries. The southeastern blueberry bee was the most effective pollinator overall and was consistently found in some fields across all years. Bumble bees and carpenter bees were seen at low densities but did contribute to fruit set in some fields. This research can help blueberry growers by providing methods to assess the foraging activity of pollinators, which would provide information useful when making decisions about trying to enhance pollination services by either adding colonies of honey bees or by promoting native populations of wild bee species.

Technical Abstract: Field-scale data on the relationship between pollinator activity and fruit set are scarce for rabbiteye blueberries (Vaccineum virgatum syn. ashei Aiton). We measured the densities of foraging Apis mellifera L., Habropoda laboriosa F., Bombus Latreille spp. and Xylocopa virginica L. in 7-21 commercial blueberry fields during each of three years in Louisiana and Mississippi. Foraging bees were counted on 10 bushes per field on two days during bloom, and the density of bees per flower was calculated based on the number of flowers open during the counts. Fruit set was measured 30 days after bloom. The impact of foraging activity on fruit set was inconsistent when densities of either all foragers or foragers of individual taxa were considered. Strong associations were observed only in 2001, with fruit set was increased by H. laboriosa and Bombus spp. and with a weaker contribution by A. mellifera. Floral robbery by X. virginica had no negative effects. Populations of H. laboriosa was relatively consistent across sites. Managed colonies of A. mellifera were added at two densities (12.5 or 2.5 colonies per hectare) in seven fields each in 2001. These supplemental bees did not result in greater forager densities or fruit set in stocked fields. The observations show the challenge of field-scale pollination tests but provide an initial framework for rabbiteye blueberry growers to assess the availability of foraging bees early in bloom to help decide whether to add supplemental A. mellifera to try to enhance pollination if populations of non-Apis bees are low.