Honey bee (Apis mellifera) colony strength and its effects on pollination and yield in highbush blueberries (Vaccinium corymbosum)

Abstract

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.

Honey bee (Apis mellifera jemenitica) colony performance and queen fecundity in response to different nutritional practices

“…Colony performance includes colony strength and productivity ( Chemurot and de Graaf, 2019 ). The colony strength is determined by the number of adult worker bees in the hive, brood pattern, and the flight activity around the hive entrance ( Pokhrel et al, 2006 , Delaplane et al, 2013 , Taha and AL-Kahtani, 2019 , Grant et al, 2021 ) while colony productivity is measured in honey production and pollen collection ( Hoover and Ovinge, 2018 ). The physical characters of the queen are associated with colony performance and were investigated using a different behavioral attribute by Akyol et al, 2008 , Hatjina et al, 2014 .…”

The Honey Bee Apis mellifera: An Insect at the Interface between Human and Ecosystem Health

“…The presence of healthy colonies also guarantees fruit quality and quantity across seasons in both apple and pear crops [ 44 ]. The strength of the bee colonies is also decisive for promoting crop production in the northern highbush blueberry, which is self-fertile, but higher fruit set and yields occur following visitation by honey bees from healthy colonies [ 45 ]. For watermelon crops, as native solitary bees are effective pollinators but do not allow optimal yield, supplementary pollination services through A. mellifera are suggested, even if in this case native managed stingless bees are preferable because they compete less with native pollinators [ 46 ].…”

Toward evidence-based decision support systems to optimize pollination and yields in highbush blueberry

“…Combined, these functional differences based on colony size and forager population further complicate the utility of stocking density recommendations on a per colony basis. Assessing honey bee colony size can be done using the cluster size method (Nasr et al, 1990;Chabert et al, 2021) implemented with a beekeeper and/or an intermediary such as a bee broker (Goodrich, 2017), with thermographic imaging (Shaw et al, 2011;López-Fernández et al, 2018), or by assessing activity at hive entrances (Rodet and Henry, 2014;Ovinge and Hoover, 2018;Grant et al, 2021). When assessing honey bee colony sizes, it should be noted that the relationship between colony size and cluster size is exponential and not linear (Chabert et al, 2021).…”