Honey bees, Apis mellifera, are important pollinators of the highbush blueberry variety Ventura despite the inability to sonicate

Animal-mediated pollination is an essential ecosystem service which over a third of the world’s agricultural crops depend on. Blueberry fruit production is highly dependent on pollinators and in their native range they are pollinated mostly by bumble bees (Bombus spp.). Demand for blueberries has increased in recent years due to their perceived health benefits. Consequently, blueberry cultivation has expanded well beyond their native range, including several regions where bumble bees are not present. In many areas, honey bees may be the only commercially available pollinators of blueberries because many countries ban the importation of bumble bees. This study aimed to determine the benefits of honey bee pollination on blueberry fruit quality and quantity for the variety Ventura by comparing yields of honey-bee-pollinated flowers to flowers where pollinators had been excluded. Honey bees significantly increased berry mass and diameter. Our results suggest that the presence of honey bee pollinators potentially increases revenue by approximately $864 501/ha in areas without bumble bees. We conclude that Ventura is reliably pollinated by honey bees, and that honey bee pollination may be a useful substitute for bumble bees in areas where bumble bees are absent. We also determined the extent to which blueberry yields could still be improved by comparing fruit quality and quantity under honey bee pollination to fruit quality and quantity achieved through ideal hand pollination. We found that blueberry yields may be still be significantly increased relative to ideal hand pollination and we discuss potential ways to improve the efficiency of honeybee pollination in the future. Additional research is required to study how beneficial honey bees are to fruit yield on varieties as the benefits of honey bees are likely to vary across different varieties.

optimized pollination (by hand). By comparing fruit quality among these three treatments, we 97 determined whether the addition of honey bees was beneficial to blueberry production as well as 98 the extent to which pollination by honey bees could potentially be improved upon (see Fig. 1   To determine the extent to which honey bee pollination can potentially be improved, we compared 130 the honey bee pollination treatment (above) to a hand-pollinated treatment (optimized pollination).

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We assumed that hand pollination would result in the best fruit production possible by maximizing 132 the deposition of pollen. 133

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Prior to hand-pollination, Ventura flowers were emasculated. We did this by removing part of the  Fig 2A).   Fig 2C, Table 1). There was no difference in the fruit set of 214 flowers with access to honey bees relative to flowers which had no access to honey bees or hand 215 pollinated flowers (Chi-square=1.36, df=4, p=0.507) (Fig 2D).

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The beneficial effects of honey bees on fruit mass and fruit set also translated into bees to 13 ± 0.64 (mean ± SE weeks to ripen) when pollinated by hand (Fig 2A). Hand-pollinated 230 fruits were significantly heavier (Table 1) at 3.69g ± 0.23g (mean ± SE fruit mass), than flowers 231 pollinated by honey bees at 2.89g ± 0.23g (mean ± SE fruit mass, Fig 2B), a ca.27% increase. Hand 11 232 pollination did not significantly increase the size of fruits compared to fruits resulting from honey 233 bee pollination (Table 1, Fig 2C).

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However, when both mass and fruit set were incorporated into a model to calculate total 235 yield, hand pollinations resulted in significantly greater yields than honey bee pollination (Table 1).

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This study revealed that the pollination environment has the potential to strongly affect the quality 242 of fruit produced by the highbush blueberry variety Ventura. In particular, yields are greatly 243 increased by the addition of honey bees in areas where bumble bee pollinators do not occur 244 naturally, and importation is illegal. Honey bees were the only pollinators at this site and therefore 245 the effects shown are a direct result of access to honey bees, rather than other unaccounted wild 246 pollinators. This provides valuable information for the pollination of commercial blueberries, 247 particularly with respect to the underutilized role played by honey bees, and suggests some 248 important directions for research on blueberry pollination.

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We show for the first time that Ventura can produce fruit without pollinators. However, 250 these fruits are of lower quality than the fruits of flowers exposed to honey bee pollinators. This 251 ability is not unique to Ventura, as other highbush blueberry varieties can also produce fruit in the 252 absence of pollinators. However, these fruits are also of noticeably poorer quality than fruits 253 produced by flowers with access to pollinators [5,6,15]. The presence of honey bees significantly 254 increased blueberry yields by improving fruit quality through greater fruit diameter and mass (Fig. 2).

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This shows that despite honey bees' inability to buzz-pollinate, they do extract blueberry pollen from 256 anthers and transfer it to stigmas. Thus, in areas lacking native blueberry pollinators, the addition of 257 honey bees may increase blueberry yields by more than 150% (Fig 2E).