Many pollination studies with honey bees have examined the effect of colony density on crop yield and yet overlook the effect of variation in the population size of these colonies. High colony density in northern highbush blueberry has been met with concerns from beekeepers who feel higher densities will intensify outbreaks of European foulbrood (EFB, Melissococcus plutonius, Truper and dé Clari), a honey bee brood disease. The purpose of this study was to confirm the prevalence of EFB in colonies pollinating blueberries and to determine whether field-level variation in the population of adult workers in colonies explained variation in blueberry fruit set and/or yield. We addressed these objectives over the course of two production seasons at 13 commercial blueberry fields in Oregon, USA, stocked with identical densities of 10 colonies/ha. We confirmed that all colonies had negligible symptoms of EFB at the start of blueberry pollination, but 53% of colonies in 2019 and 41% in 2020 had symptoms immediately following the pollination season. We also validated a method for rapidly assessing adult honey bee colony populations, namely by counting the rate of foragers returning to colonies, and it was found to be strongly correlated to true internal adult bee population independent of year and ambient temperature at the time of evaluation. Using returning forager counts, we determined there was considerable variation in the average population of colonies at each field, ranging from an estimated 10,300 to 30,700 adult worker bees per colony. While average colony strength did not predict variation in fruit set, it was related to variation in yield, independent of year. Our linear model of flight count (as a proxy for colony strength) predicts estimated yield increases of up to 25,000 kg/ha of blueberries could be achieved by colonies stronger than the recommended six frame minimum, suggesting that higher pollination benefits could be achieved without increasing hive density if stronger colonies are promoted.

中文翻译：

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蜜蜂（Apis mellifera）群体强度及其对高丛蓝莓（Vaccinium corymbosum）授粉和产量的影响

许多蜜蜂授粉研究已经检查了菌落密度对作物产量的影响，但忽略了这些菌落种群规模变化的影响。北部高丛蓝莓的高菌落密度引起了养蜂人的担忧，他们认为更高的密度会加剧欧洲臭虫（EFB、Melissococcus plutonius、Truper 和 dé Clari）这种蜜蜂育雏疾病的爆发。本研究的目的是确认授粉蓝莓的群体中 EFB 的流行，并确定群体中成年工人种群的田间水平变化是否解释了蓝莓坐果和/或产量的变化。我们在美国俄勒冈州的 13 个商业蓝莓田的两个生产季节中实现了这些目标，种植密度相同，为 10 个菌落/公顷。我们确认所有菌落在蓝莓授粉开始时都具有可忽略不计的 EFB 症状，但 2019 年和 2020 年分别有 53% 和 41% 的菌落在授粉季节后立即出现症状。我们还验证了一种快速评估成年蜜蜂群体数量的方法，即通过计算觅食者返回群体的比率，并且发现它与真实的内部成年蜜蜂群体密切相关，独立于评估时的年份和环境温度. 使用返回的觅食者计数，我们确定每个田地的平均蜂群数量存在相当大的差异，估计每个蜂群有 10,300 至 30,700 只成年工蜂。虽然平均菌落强度不能预测坐果的变化，但它与产量的变化有关，与年份无关。