A mason bee, Osmia ribifloris, as a potentially manageable pollinator of cultivated blueberries in the South

Managing megachilid bees often involves establishing small genetically uniform populations within agricultural settings very different from the bees’ native habitat. Among select populations of Osmia ribifloris used in our blueberry pollinator program, mtDNA (COI) markers show two very distant populations from different subspecies actually shared the closest phylogenetic kinship. In fact, the fittest adult females originated from Texas and California. These bees, when kept in captivity, provisioned the largest and healthiest broods using blueberry pollen. Osmia ribifloris from northern Utah, their Mississippi progeny, along with a floral generalist from east Texas (O. lignaria) produced comparatively fewer brood. Interestingly, reproductive fitness of O. ribifloris also depends on a female’s reproductive status. Namely, mated bees out-produced unmated bees. Mated bees nest 2 weeks earlier and produce broods that are twice as heavy. Unmated bees in fact exhibited counter-productive behaviors; 22% of them aggressively usurped active nests and in the process killed 67% of brood, a huge loss of potential blueberry pollinators. Such high rates of infanticide as well as a steepening rate of male production indicate declining growth for such a small captive bee population. Thus, prompt releases of wild O. ribifloris into blueberry fields with ample forage and nests are preferable to long-term captivity and its risk of unstable secondary sex ratios and facultative nest parasitism.