Controlling bumblebee nest boxes based on incoming sunlight and screening

'Innovative software helps improve bumblebee pollination in artificially-lit greenhouses'

Growing tomatoes under artificial lighting requires special care to ensure proper fruit setting, since these conditions make it difficult for bumblebees to do their job.  Wireless bumblebee nest boxes (called 'bee homes') now tend to be opened and closed at fixed times, while controlling the bee homes based on the incoming sunlight and operation of the screens would seem more logical. HortiMaX has designed new climate computer software to do just that. As with many successful innovations, the strength of this software lies in its apparent simplicity and logic.

Kesgro, a pioneering tomato nursery in the Netherlands, has just started a new crop under artificial lighting. While the staff are hard at work twisting the plants, the bumblebees buzz back and forth pollinating the flowers. There is still plenty of sun at this time of year, so there are no problems with fruit setting. It's a different story when the days grow shorter, the lamps go on and the screens close. With red light flooding the greenhouse, the bumblebees become disoriented.  They need natural, ultraviolet light to see and navigate.  It's well-known that artificial lighting can have serious impact on the bumblebees.

Screen-based control
Joost Veenman of HortiMaX, who's had a penchant for the flying workers since he was young, wondered whether it wouldn't make more sense to open and close the bee homes based on the incoming sunlight and screening, as opposed to the common practice of operating the hives at fixed times of the day. This led HortiMaX to design new control software, now available for their CX500 and MultiMa climate computers. Remco Huvermann from Koppert Biological Systems plans to monitor bumblebee activity using counters and assess the fruit setting at Kesgro this winter. He finds this particularly interesting, because there is still much to learn about bumblebees and pollination.

Time setting
The 37-hectare tomato nursery has a total of 400 bee homes. Paul Groot Scholten tells us: 'When we had a research greenhouse in the advent of grow lighting, we soon began to notice that the bumblebees were dying.' Now, thirteen years later, much more is known about the cause. 
He now controls the opening and closing of the bee homes with a time setting, including a safe margin. This is not an ideal solution.  There are still wintry days when it's better for the bumblebees to stay inside and when he keeps the bee homes closed. The bumblebees can cope with that, provided it doesn't last too long. 'The screens stay closed at least one day every year. We've had quite a few Christmases when fruit setting was poor. Screening is our main concern', he explains.

Two hours needed
The current recommendation for November is to let the bumblebees fly out between 10:00 and 15:00.  It's best to do so two hours after sunrise until two hours before sunset and, if possible, only when the screens are open. Grootscholten knows from experience that the flight holes of the bee homes should close one and a half hours before the screens close, so the bumblebees have enough time to return to the bee homes before their natural GPS, the sun, is gone. 'Closing the bee homes at the right time in relation to the screens is crucial, so the bumblebees can make it back in time,' according to the grower.

Huvermann: 'The bumblebees need about two hours a day to pollinate all the new flowers.' Since a flower blooms twelve hours a day for two to three days, the bumblebees have several opportunities to pollinate the flower. An extra complication in growing tomatoes under artificial lighting is that there are far fewer effective pollination hours compared to cultivation without artificial lighting. The artificial lighting switches on at night and the flowers start closing at midday. If the screens also close due to extreme cold or snow, the bumblebees sometimes have less than the two hours needed to do their pollination work.

Opening hives based on incoming sunlight
The new control software for the HortiMaX climate computers links the wireless bee homes to the incoming sunlight and the opening and closing of the screens. The software that coordinates this process is simple but unique, allowing growers to set their own preferences.
Since the tomato grower must comply with strict light emission regulations, the screens are not only used to save energy, but also to block light from the greenhouse using a special foil.  The main challenge in terms of the control process is when the screens close earlier than expected. The software keeps an exact record of when and how long the bumblebee hives were open and closed.   This provides new insights for the grower and his pollination specialist. 'That's why we're closely monitoring the changes in fruit setting this winter,' says Veenman.

Bumblebee counter
'We want to determine how long the bee homes are open and examine when pollination problems could occur due to the bee homes closing at the wrong times or the flying periods not overlapping with the times when the flowers are open.' 'We've fitted a 'bumblebee counter' to the closing unit of each bee home, so we can record exactly what is happening," adds Huvermann.
Veenman: 'There are, of course, several ways of improving fruit setting, one of which is to simply use more bumblebees.' In short, keeping track of the bumblebees this winter could not only prevent a reduction in fruit setting, but may even help to improve it.   'The first step is obviously to avoid losses from unpollinated flowers", says Veenman. 'This will help make life easier for the grower.'

Translation of article published in 'Onder Glas', October 2013.

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