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Pollination in crops grown under artificial light in dark weather conditions
The dark weather conditions in the winter months create orientation problems for bumblebees. The spectrum of artificial light is barely visible to bumblebees as it consists primarily of red light. With a little daylight, the bumblebees will generally be able to find the flowers, but if there is no sunlight or if the sun's rays are fully filtered, they will be unable to navigate well enough to find their way back to the hive.
At this time of year, the light levels in the early hours of the day are not always sufficient for the bumblebees to be able to find their way around optimally. In the winter, the sun is at its lowest in the sky. In addition, the rest of the UV light - which helps the bumblebees to navigate - is often filtered by clouds, energy screens, and matt glass, or absorbed by snow.
A number of guidelines are presented below, in addition to our standard positioning advice:
Extending the lighting cycle
Recommendation: Avoid nights that are too short (i.e. less than six hours).
Influence of the lighting cycle on the opening and closing of the flowers
Recommendation: Bumblebees usually need at least 1.5 hours of effective daylight in order to pollinate all the flowers in the greenhouse. The recommendation is not to begin the lighting cycle before 1:00 AM (i.e. during the night) as this could lead to the flowers closing before 12:00 noon, leaving the bumblebees with insufficient time to pollinate all the flowers.
Effect of energy-saving screens/insulation
Recommendation: Ensure that the screens are open at the times when the bumblebees are able to leave the hive (i.e. when the Wireless Beehome systems are open). The screens must not be closed while the bumblebees are still flying around, as many bumblebees could then become trapped above the screens, where they would not survive overnight. Since the side walls of the greenhouse are often covered with insulation screens, it is better to only allow the bumblebees to fly out of the hive once the sun has risen above the height of the side walls. Polycarbonate side walls reflect a great deal of UV light in all directions, creating a 'disco light' effect which disrupts the bumblebees' orientational ability.
Lack of ventilation
Recommendation: Reduce the ventilation only when necessary, keeping a close watch on ethylene production.
Effects of artificial lighting on the greenhouse climate
Recommendation: Keep a close watch on the climate (temperature and relative humidity) and increase the ventilation when necessary. If the relative humidity is above 80%, the pollen doesn't release as easily.
Recommendation: Keep a close watch on pollination and if there is insufficient natural pollination, release extra bumblebees or pollinate by hand. Remove snow from the greenhouse as necessary.
Recommendation: Keep a close watch on pollination and if there is insufficient natural pollination, release extra bumblebees or pollinate by hand.
Recommendation: Make sure that the bumblebees have enough time to fly while the flowers are open (at least 1.5 hours per day) so that they can collect enough pollen. Also make sure that the flowers are attractive enough to bumblebees (plants in a highly vegetative state, powerful viruses, pesticides, etc., can make flowers less attractive).
For the correct approach, please consult a Koppert specialist or a recognised distributor of Koppert products.
IMPORTANT: There are known cases where bumblebee colonies have lost all foraging bumblebees in just two hours because the advice relating to using the colony was not followed. If it is not possible to follow the advice, it is better not to let the bumblebees fly on that particular day and to wait until the following day to open the hive. Never keep the hive closed for longer than one day.