Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/11/2004
Publication Date: 2/11/2004
Citation: Sampson, B.J., Danka, R.G., Stringer, S.J. 2004. Nectar robbery by bees [xylocopa virginica (l.) and apis mellifera l.] contributes to the pollination of rabbiteye blueberry. Journal of Economic Entomology. v.97 p. 735-740. Interpretive Summary: Carpenter bees are often abundant when rabbiteye blueberries flower in March and early April. These bees usually pierce the base of the blueberry corolla to access nectar near the bottom of the pistil. Such robbery visits in which the corolla opening is bypassed may result in bees failing to pollinate flowers because pollen receptive stigmas are located at the top of the pistil and opposite where robbery slits normally occur. Nectar robbery slits produced by carpenter bees presumably provide honeybees with easier access to nectar. This type of floral larceny or robbery by carpenter bees and honeybees is thought to hinder fruit production. However, these earlier claims may have been misleading because a nectar-robbing honeybee transfers as much pollen as a legitimate forager or carpenter bee and multiple robbery by both honeybees and carpenter bees (as few as 2-3 visits) can effectively pollinate blueberry blossoms. In the field, carpenter bee robbery does not contribute to lower fruit sets. Therefore, nectar robbing carpenter bees and honeybees are not detrimental to blueberry pollination or production, and where abundant they could actually bolster fruit set and yield.
Technical Abstract: At the flowers of rabbiteye blueberry, honeybees probe for nectar from robbery slits previously made by male carpenter bees. This relationship between primary nectar robbers (carpenter bees) and facultative nectar thieves (honeybees) is seemingly unfavorable for blueberry pollination. We designed two studies to measure the impact of nectar robbers on rabbiteye blueberry pollination. First, counting the amount of pollen individual robbing and non-robbing bees delivered to unvisited stigmas was a measure of pollination efficacy. Both primary robbers and legitimate honeybee visitors were individually less efficacious and deposited fewer tetrads per stigma than did our benchmark pollinator, the southeastern blueberry bee. Increasing numbers of visits by carpenter bee robbers and honeybees produced larger stigmatic loads. Loads noticeably declined when robbery slits increased to four per corolla. In a second study, a survey of ten commercial blueberry farms tested whether corolla slitting by carpenter bees (i.e. robbery) influenced rabbiteye blueberry fruit set. Slitting was not negatively correlated with fruit set, and therefore, floral robbery should not concern southern blueberry producers. Robbers may even benefit blueberry pollination and greater effort should be devoted to retaining all pollinator species.