Bees and bumblebees are, thanks to their build and behaviour, good pollinators. But they have additional potential. They are also useful for disease control by transferring antagonistic microorganisms and for retrieving information about diseases in the fields. An important aspect for all these tasks is: How do we keep them working under the ‘new’ growing conditions in the greenhouse?
Sjef van der Steen, researcher in the department Bio Interactions and Plant Health at Plant Research International, Wageningen, the Netherlands, researched the additional possibilities for these pollinators such as in disease control and air quality detection.
His research considered two questions: Is crop protection via bees and bumblebees effective and is it safe for these creatures? He provided the bees with the antagonist Trichoderma that works against Botrytis. The bees introduced sufficient Trichoderma onto the plant to prevent it becoming diseased. The substance had no effect on bees and bumble bee families.
Exit and entry opening
Then he carried out exploratory research into possible ways to establish a system in which the incoming and outgoing flow of bees could be separated. He placed a small type of aquarium pump at the exit route that continually released fresh spores.
The principle was picked up and further developed by Biobest. Meyers Softfruit, of Riemst, Belgium, has been using this method for two years. The bumblebee hives are equipped with an entry and exit opening. A powder dispenser is integrated into the exit opening. When a bee flies away it automatically takes with it some of the fine powder to the leaves and flowers. It was first tried out with the biofungicide VerderaB4. This is the first substance that has been permitted for this application. This year Van der Steen will join on-going Dutch research in Bleiswijk once new antagonists have being selected.
During their flight back from the flower the bees carry with them not only pollen but also other ‘information’ such as bacteria and fungi which have carried by air into or onto the flower. By analysing which disease or pest is present it’s possible to take timely action before the symptoms become visible. In order to get a good picture of what exists, the researcher had to make a number of choices. Where to place the colony of bees? How many colonies do you need? How do you ensure that the bee colony flies to a certain crop?
The next step was to take samples. He used two methods for obtaining the bacteria or fungi for analysis. “One method involves pulling the bees off the flight path, killing them and then immersing them. By using the other method the bees remain alive. We get them to walk through a tube containing a sticky material. Part of what they carried with them remains in the tube.” For both methods the researcher created a solution containing the pathogens for analysis later.
Diseases on flowers
Van der Steen decided to use two different methods of analysis: One uses a reagent; the other DNA-analysis. For the first method he uses a lateral flow device (lfd): a double plastic strip with a piece of reagent paper sandwiched between that discolours when a certain fungus or bacteria is present. Prime Diagnostics of Plant Research International supplies such papers containing a reagent that detects various common diseases.
For DNA-analysis he uses a portable PCR-analyser (poly chain reaction). “We used this method two years ago in cooperation with Agis, an Austrian institute for quality in agri- and horticulture to detect fire blight in fruit. We have used them in the Netherlands for detecting bacteria in strawberry and brown rot in cabbage. The results show that bees and bumblebees only carry with them diseases that are present on flowers. This method doesn’t work for leaf diseases, such as brown rot in cabbage.”
Air quality detector
Thinking further ahead Van der Steen sees opportunities for bees to take samples ‘passively’. A honeybee colony spreads itself out over the landscape while searching for food. As well as pollen and nectar they carry ‘other material’ with them to the hive. By taking samples of this and analysing it you get a picture of the diseases that are present in the environment. “The limitation of this method is that it only works with flowers. On the other hand, the possibilities are great. Everything that is spread through the air can be found on the flowers, not only plant diseases, but also bacteria that cause Q-fever, for example,” says the researcher. Van der Steen does see possibilities for using bee colonies as ‘air quality detectors’. “Outside West-Europe, where you don’t find these poles that detect air quality we can use bee colonies as cheap indicators of the environment.”
One of the conditions for using bees and honeybees, whether it is for pollination or disease control, is that the (flying) conditions must be good. Among other things this depends on the greenhouse roof material and the lighting.
Effect of lighting
With the arrival of assimilation lighting the greenhouse conditions, which are already different to outside, are changed even further. Ten years ago, colleague Tjeerd Blacquière who was doing research into the direct effects of high light levels on pollinating insects saw that assimilation lighting affected both these pollinators and the crop as, among other things, the amount of light, duration of light, light spectrum (more heat radiation), the day length and the direction of the light changed. Artificial lighting also altered the vigour of the crop and the day-night rhythm of flowering.
A few years ago Blacquière offered a few suggestions: Set the timing of the lighting so that the opening of the flowers occurs at the most optimal hour for pollination. Close the exit opening of the hives (automatically) well before sunset to prevent (a lot of) workers trying to fly away from the hive in poor light. A few hours of light during the peak in flower opening – during the middle of the day – is sufficient. Research showed that in February around 10 am all sweet pepper flowers had already been stripped of pollen by honeybees.
Use lamps with a better spectrum. Pure red LEDs are probably the most ideal for bees and honeybees. They don’t see red light at all.
Different roofing materials
Blacquière also carried out exploratory research into the impact of using various roofing materials such as glass, polymethylmethacrylate and polycarbonate on the foraging behaviour of bees. In the glass greenhouse the sun was visible as a bright spot in the sky. In the polycarbonate greenhouse the light was scattered into a light arch along the entire firmament. An arch shaped distribution of light was visible to a lesser effect in the polymethylmethacrylate greenhouse.
All the greenhouse roofs allowed PAR-light to enter well. Ultraviolet is hardly transmitted by polycarbonate, partially by glass and completely by polymethylmethacrylate. After introduction to the greenhouse, bees and bumblebees showed normal orientation behaviour under a greenhouse roof of glass and polymethylmethacrylate. Under polycarbonate the bees and bumblebees failed to return to the hive.
In addition to being pollinators, bees and bumblebees are also useful for crop protection. They can carry antagonists to pests and thereby prevent diseases from developing. In addition they can act as air quality detectors because apart from pollen they also carry back bacteria and fungal spores, providing the flying conditions are good.
Text/photos: Marleen Arkesteijn