In collaboration with Marlene Jennings and Jonathan Jakes

Originally published in Hivelights

Transporting honey bees can be risky. On top of hazards like leaking bees or shipping delays, extreme temperatures can damage the queen’s fertility and reduce the productivity of the colony. With more and more extreme weather events, combined with growing interest in domestic sustainability of bee supplies, it is time to re-evaluate how and when we ship bees.

Hot and cold temperatures can cause queen infertility by killing the sperm stored within the spermatheca, and my previous research has shown that failing queens have more dead sperm than healthy queens. So far, most studies have focused on temperature fluctuations in shipments of caged queens, where the bees have trouble thermoregulating and are vulnerable to temperature spikes.

Temperature fluctuations within nucs, however, have seldom been investigated, despite the fact that nucs are also shipped within and between provinces and territories. One study tracked temperatures in box-style packages shipped on a flat-deck truck in the U.S., and identified a link between temperature fluctuations and subsequent colony outcomes. But enclosed nucs with frames of bees and brood may experience different temperatures, since nuc shipping boxes are generally not as well ventilated as packages.

Methods:

In June 2021, we (Marlene Jennings, who runs Behind the Barn, and Jonathan Jakes, manager of Urban Bee Supplies) investigated temperature fluctuations in three shipments of nucs that were delivered from Vancouver to Whitehorse via Air North Ltd. Months ahead of time, a plan was agreed upon by the airline and supplier to ship three batches of 16 nucs each. The nucs were produced locally in BC’s lower mainland and made up of four frames of bees, brood, food, and drawn comb contained in Ontario-style corrugated plastic shipping boxes. The boxes were engineered to have extra vent holes (approximately 180 cm2 total meshed ventilation, or 60 cm2 each), such that each box had one vent on the top and two on opposite sides. Shipment 1 was scheduled for June 1st, Shipment 2 on June 2nd, and Shipment 3 on June 7th).

The nuc boxes were strapped to a shipping pallet and spaced to avoid obstructing the vent holes. We included temperature loggers taped under the lid of a subset of boxes in each shipment, with the loggers sealed in stamped envelopes for the recipient to mail back to the UBC laboratory. Each nuc was also enveloped in a light mesh transport bag to prevent bee leaks. Upon arrival in Whitehorse, Air North accommodated an immediate pick-up for the bees from the airport, and the boxes were kept outside in the shade until the recipients arrived to claim their nucs.

Nuc shipment orientation. Combined layers show the final nuc arrangement on the shipment pallet.

Results:

The daily highs in Vancouver for the three respective shipment dates were 24.1°C, 28.2°C, and 15.6°C (airport data obtained from Environment Canada). In Whitehorse, the corresponding daily highs were 17.8°C, 17.2°C, and 19.4°C. We obtained temperature data for four, six, and two nucs in shipments 1, 2, and 3, respectively (designated as nucs 1 – 12; not all temperature loggers were returned). We found that under the lid, temperatures fluctuated from 20°C up to 48°C in one instance (nuc 5) – well beyond the “safe zone” for queens, which is defined as 15 – 38°C based on the best available data.

Worker honey bees have been previously shown to die at 48°C, and indeed, the nuc in Shipment 2 experiencing extreme heat unfortunately perished during transit. Other nucs (nucs 6, 8, and 9) in Shipment 2 experienced temperatures between 39°C and 41°C, a range which can lead to partial loss of queen fertility but which does not cause worker mortality.

Temperature data for three shipments from Vancouver to Whitehorse. Each color corresponds to a different nuc. The black bar indicates the time during which the nuc was in flight. Time = 0 h corresponds to midnight prior to departure.

Recommendations:

Several factors could influence the outcomes for shipped nucs, such as ambient temperature at the departure and arrival locations, ambient temperatures during transit, bee density within the nucs, construction material of the nuc boxes, and degree of ventilation. Ambient temperatures were the hottest on the day of Shipment 2, which was also the only shipment with nuc mortality. The temperature of the Shipment 2 nucs was stable in the early morning but began climbing ahead of the actual flight, which indicates that the ambient temperature on the ground in Vancouver probably contributed to loss of life. Future shipments should aim to depart at night or early in the morning, if possible, to avoid high temperatures during the late morning and afternoon. If airline delays push departure times into the late morning or afternoon, the shipment should be cancelled to ensure animal welfare.

Honey bee density within the nuc may have also been a contributing factor. Strong (populous) nucs are desirable in order to grow into robust colonies once received by the beekeeper, but having too many bees in a confined space could elevate risk of temperature stress during transit. One way to help avoid this problem may be to use nuc boxes constructed of a more breathable material (e.g. un-waxed cardboard or framed wire mesh), more like package bee containers, that can still allow for evaporative cooling. The nuc boxes used in these shipments are designed for shipping, and even had extra vent holes than the standard design. There was ample ventilation for oxygen flow but this was apparently not enough to enable sufficient cooling. Different materials should be tested to find the best balance between structural integrity and ventilation capacity, so that shipped bees can have the best outcomes possible.

Acknowledgements:

Thank you to all the Yukon beekeepers who returned the temperature loggers! We appreciate your support for this study.

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