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Science Insider

The Blueberries and the Bees

- July 1, 2018 - Alison McAfee - (excerpt)

beekeepers tending to hives

Thousands of honey bee colonies arrive in the Fraser Valley’s blueberry fields every spring, but beekeepers are worried this crop may be harming their bees.

My alarm only managed to announce one jolting ring before I slapped it off. The clock read 3:45 am, and there was no time to waste. Bleary-eyed, I threw together a thermos of coffee for the road and grabbed the day bag I had packed the night before, complete with sunglasses, 2 bottles of water, granola bars, and a pillow for the long car ride ahead. My colleague, Bradford Vinson, arrived to pick me up at 4:00 am on the dot. I jumped in his pick-up truck and we headed out to the Valley.

Bradford and I were bound for the blueberry fields in Agassiz, a small town in the Fraser Valley of British Columbia, two hours east of Vancouver. There, forty honey bee colonies were waiting for us – all New Zealand packages established earlier in the year – which had just been placed in the blueberry plots to fulfill pollination contracts.

Blueberries are Canada’s biggest fruit export, generating about $400 million in revenue annually. Most of those berries are grown in BC and rely on honey bee pollination for reliable fruit set. But over the last few years, beekeepers have voiced growing concerns over the health of their blueberry-pollinating colonies; in particular, an unusually high incidence of European foulbrood (EFB) disease and a yet-unidentified “snotbrood disease,” which looks similar to EFB but comes back as negative in diagnostic lab tests. Some beekeepers have even indicated that they will decline to participate in blueberry pollination in the future at a scale that could create a major pollination deficit. Too many commercial beekeepers have reported similar concerns to ignore, and it’s time for the issue to be investigated with scientific rigor. We are even willing to get up at 3:45 am to do it.

Heather Higo and Marta Guarna, the project managers, met us in the field to help with the long day of work ahead. We were about to interrogate these colonies for the five most prominent indicators of colony health we could think of: pollen quality, honey quality, amount of brood, presence of diseases, and the size of the adult population. The previous day, we had sampled and measured the same things in forty colonies which were established from the same package source but spared of any agricultural pollination duties. As more Fraser Valley beekeepers got the call to move their colonies into the fast-approaching blueberry bloom, we evaluated a further 120 hives with various genetic origins at four other field sites, creating one of the biggest experiments on bee health in blueberries to ever be conducted.

This isn’t the first time that beekeepers have questioned the impact that blueberry pollination has on their colonies. In the 1980s, Gordon Wardell devoted an entire PhD thesis to the topic of European foulbrood’s association with blueberry pollination in Michigan.1 He found that there might be a link between the acidity of the pollen and EFB susceptibility; that is, larvae on a diet of less acidic pollens (like blueberry and cranberry, pH 6.0-6.4) were more susceptible to the disease than larvae on a diet with more acidic pollens (like alfalfa, pH 4.4). Interestingly, he found that the same trend held true for more acidic and less acidic pollen patty supplements. In his thesis, Wardell proposed that the mechanism could be rooted in the diet’s ability to change the acidity of the larva’s gut, once ingested.

The logic is that Melissococcus plutonius – the causative bacterial agent of EFB – thrives in less acidic conditions, so the less acidic diet may be having a Goldilocks effect. It’s making the larval gut environment perfect for M. plutonius to multiply. Likewise, the more acidic diet was making the gut less appealing, offering a protective effect. Based on these findings, Wardell developed a nutritional supplement – MegaBee pollen patties – with a carefully adjusted pH to help counteract the low acidity of blueberry pollen. It’s still on the US market today.

Wardell’s experiments were easily the most detailed investigation into the link between EFB and blueberries, but they weren’t the last. Dean Polk, a county agent at the New Jersey Agricultural Experimental Station, reported that similar blueberry-associated EFB and “snotbrood” concerns are being raised by beekeepers on the East Coast of the US. Polk raised this point at the Entomology Society of America conference in Denver, Colorado last November and had conducted a small-scale field experiment to investigate the issue.2

In Polk’s study, the researchers monitored brood area and pesticide residues in commercial hives for the blueberry and cranberry pollination rounds in 2015, ’16, and ‘17. They found that the colonies’ brood areas decreased during the pollination period; however, their ability to draw further conclusions was limited, partially because relatively few colonies were sampled and partially because there were no comparisons to colonies from the same source, but which didn’t participate in blueberry or cranberry pollination. And that is a very important comparison to make, because otherwise skeptics can (reasonably) argue that any decline in colony health could be simply due to other environmental factors like a long bout of bad weather or an outbreak of EFB across all colonies – not just those in blueberries.

So, while concerns over bee health in blueberries have been voiced before, this is the first time it has been investigated at such a large scale. So far, whether there is a significant difference in disease incidence between blueberry pollinating and non-pollinating colonies is unknown. That’s what we hope to find out, and if so, what we can do about it. To get a head-start on addressing the latter, we are not only measuring the health of colonies in and out of blueberries, we are also testing if Wardell’s MegaBee pollen patties can improve colony outcomes in a large-scale, industrial setting, whether the blueberry-pollinating colonies are more EFB-afflicted or not. After all, pH might not be the only benefit of using a pollen supplement.

Blueberries are a notoriously difficult forage source for honey bees. The opening of the bell-shaped flower is usually too narrow for honey bees to efficiently ….