Much to be gained by the 'smarter' opening and closing of bumblebee nest boxes

Higher pollination rates in artificially-lit tomato nurseries

The 'smarter' opening and closing of bumblebee nest boxes results in more pollination time and thus higher pollination rates. This was shown by tests conducted in the greenhouse facilities of Dutch tomato producer KesGro earlier this year. The research has provided new insights and knowledge about the behaviour of bumblebees and bumblebee colonies in artificially-lit tomato nurseries.

Bumblebee pollination in artificially-lit tomato nurseries can sometimes be a problem in the winter months, especially on days with limited daylight. Since the flowers usually close around noon, the bumblebees only have a short time to do their jobs. This may result in a lower pollination percentage than normal.

In autumn 2013, Koppert Biological Systems and HortiMaX discussed the idea of controlling the Wireless Beehome system (WBH), which regulates the opening and closing of the bumblebee nest boxes, from a climate computer. The companies developed a special bumblebee software module which not only opens and closes the nest boxes based on the pre-set clock times, but also takes into account sunrise and sunset times, solar irradiance (incoming sunlight) and the position of the screens. This method provides more effective pollination time for the bumblebees and thus a higher pollination rate of the crops.

Artificially-lit greenhouses
Until recently, the standard recommendation was to open the nest boxes automatically between 10 a.m. and 3 p.m. (relatively the brightest part of the day). If the screens close before 3 p.m., it is best to close the WBH flight holes half an hour before the screens close. This gives the bumblebees enough time to return to their nest boxes.
In order to pollinate all the flowers in the greenhouse, bumblebee colonies require at least two hours a day and sufficient daylight. This means that in most artificially-lit greenhouses the nest boxes must open at 10 a.m., as the flowers close around noon on days that the lights switch on at midnight. Every minute of extra pollination time allows more flowers to be pollinated.

Test regimes
To conduct the research at KesGro, the new software module was used to program 10 ‘test regimes’ with different opening conditions in the company's climate computer. These variations in the opening conditions included different levels of solar irradiance (in W/m2), various sunrise times and whether or not the screens were open. The researchers determined which of the regimes resulted in the highest total, but above all the highest effective, pollination time.
Controlling the nest boxes based on solar irradiance proved to be extremely effective. The test that produced the best results was when the nest boxes were opened once a smoothed solar irradiance of at least 30 W/m2 was reached and the nest boxes always opened at 10 a.m. These conditions resulted in an additional 9.8% effective pollination time in both December and January. That is a significant improvement if you consider that bumblebees have only two hours a day to pollinate the flowers with the current WBH control regime.

Return-to-nest time
The research confirmed the theory that the quantity of light in the greenhouse affects the time it takes the bumblebees to fly back to the nest. On different days, the researchers observed how long it took before all the bumblebees had returned to the nest boxes after the WBHs had been shut. This total duration was linked to the average light intensity during the observation period. It showed that bumblebees required less time to return to their nest boxes on bright days than on dark days. This means that on dark days the nest boxes must be closed at least two hours before the screens close, otherwise as much as 10% of the bumblebee population may be lost on a daily basis.

The research has provided new insights and knowledge about the behaviour of bumblebees and bumblebee colonies in artificially-lit tomato nurseries. Graphs and tables allow growers to see precisely when and how long the nest boxes were open. The research project will continue in the coming lighting season.

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