Managed honeybees and South American bumblebees exhibit complementary foraging patterns in highbush blueberry

Abstract

Despite Apis mellifera being the most widely managed pollinator to enhance crop production, they are not the most suitable species for highbush blueberries, which possess restrictive floral morphology and require buzz-pollination. Thus, the South American bumblebee Bombus pauloensis is increasingly managed as an alternative species in this crop alongside honeybees. Herein, we evaluated the foraging patterns of the two species, concerning the potential pollen transfer between two blueberry co-blooming cultivars grown under open high tunnels during two seasons considering different colony densities. Both managed pollinators showed different foraging patterns, influenced by the cultivar identity which varied in their floral morphology and nectar production. Our results demonstrate that both species are efficient foragers on highbush blueberry and further suggest that they contribute positively to its pollination in complementary ways: while bumblebees were more effective at the individual level (visited more flowers and carried more pollen), the greater densities of honeybee foragers overcame the difficulties imposed by the flower morphology, irrespective of the stocking rate. This study supports the addition of managed native bumblebees alongside honeybees to enhance pollination services and emphasizes the importance of examining behavioural aspects to optimize management practices in pollinator-dependent crops.

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

“…Cross-pollination can also result in a decrease of ripening time (Supplementary Table 1) and an increase of anthocyanin content (Doi et al, 2021). Insect pollinators vary in their efficiency in cross pollination: high pollen loads on their bodies combined with foraging behavior across rows and cultivars can facilitate greater cross pollination by bumble bees (Miñarro and García, 2021), although in some cases honey bees have been observed to alternate between cultivars more than bumble bees (Estravis-Barcala et al, 2021b). Northern and southern highbush blueberry cultivars have similar levels of heterozygosity (Brevis et al, 2008) and are consequently similarly prone to EID.…”

“…Quantity and quality of blueberry rewards can also drive floral visitation rates. Honey bees primarily collect nectar from blueberry flowers and may respond to differences in nectar volume and sugar concentration found across cultivars (Jablonski et al, 1985;Bozek, 2021;Estravis-Barcala et al, 2021b). Bumble bees more frequently collect blueberry pollen than honey bees (Bobiwash et al, 2018;Miñarro and García, 2021) and may be affected by pollen traits including pollen chemistry, which has been found to differ across wild and cultivated blueberries and to affect bumble bee foraging preferences in other systems (Vaudo et al, 2016;Egan et al, 2018).…”

“…Honey bees have long been used for highbush blueberry pollination because their large population sizes and ease of transport facilitate the high densities needed to meet pollination requirements (Tuell and Isaacs, 2010a;Estravis-Barcala et al, 2021b;Mallinger et al, 2021). Stocking recommendations and practices are highly variable: earlier guides recommended stocking rates ranging from 1.2 to 25 honey bee colonies per hectare (Delaplane et al, 2000;Rucker et al, 2012), while current practices can range from 0 to 40 colonies per hectare (Gibbs et al, 2016;Mallinger et al, 2021).…”

“…Colony stocking rate is poorly correlated with honey bee visitation and thus with blueberry yield, although honey bee visitation rates have been positively correlated with yield (Supplementary Table 2). Honey bees can become diluted in the landscape when there are natural habitats or other blooming entomophilous crops, and they can also be attracted to some cultivars more than others, resulting in poor correlation between stocking rate and managed bee density in the field (Díaz et al, 2013;Gaines-Day and Gratton, 2016;Quinet et al, 2016;Estravis-Barcala et al, 2021b;Osterman et al, 2021b). Furthermore, there may be interactive effects between honey bees and wild bee densities that could affect pollination outcomes (Eaton and Nams, 2012).…”

“…These target densities can be assessed either empirically (Reilly et al, 2020;Chabert et al, 2022), or with a modular approach (Ne'eman et al, 2010;Garibaldi et al, 2020). With the modular approach, pistil receptivity lasts at least 4 days in highbush blueberry (Moore, 1964;Young and Sherman, 1978;Krebs and Hancock, 1990;Kirk and Isaacs, 2012), flowers require 5 to 15 bee visits to maximize fruit weight (Danka et al, 1993;Rogers et al, 2013;Kendall et al, 2020), and honey bees visit about 5 blueberry flowers per minute (Shaw et al, 1939;Estravis-Barcala et al, 2021b;Sun et al, 2021). Based on the assumption of 6 hours of daily foraging activity, one blueberry field would require about 0.07 to 0.2 honey bees per 100 flowers (i.e., 0.2 to 0.6 honey bee visits per flower per hour).…”