The flower, pollination and fertilization
•The sweet cherry (Prunus avium) flowers are white and occur in clusters of 2-5 on short lateral spurs. Each flower has 5 sepals and 5 petals, one upright pistil with an ovary and 2 ovules and about 30 stamens.
•The flower opens for 3-5 days. The stigma is receptive before the anthers release pollen. Ample quantity of nectar rich in sugar (30-45%) is secreted near the base of the pistil.
•Almost all sweet cherry varieties require cross-pollination with pollen from a compatible pollenizer cultivar. Therefore main varieties and suitable pollenizer varieties should be interplanted in orchards in order to encourage good cross-pollination. Insect pollinators must be present in sufficient numbers to transfer pollen from the pollenizer to the main varieties.
•Cherry blossom in Israel takes place during the months of March-April (depending on region, variety, chemical treatments for breaking winter dormancy and the amount of chilling accumulated in winter). This is an intermediate season characterized by unstable weather, expressed by extreme temperature fluctuations that might affect insect pollinators’ activity.

The hive
•Because the cherry flower is rich in nectar, the bumblebee hive is introduced without sugar-water. The natural level of nectar in the crop is sufficient to support normal development of the bumblebee colony.
•When it leaves the factory, the standard colony for cherry consists of the founder queen, a few dozen workers, pupae, larvae and eggs. The hive does not contain males. •This is a strong colony with an anticipated life expectancy of 5-10 weeks.
 
Introduction scheme
•Ten bumblebee hives provide adequate pollination for one hectare during the entire bloom period. The hives should be introduced at about 10% bloom or less.

Placement of the hive in the orchard
•The bumblebee hive is placed on a vertical stand of 1 or 1.5 m in height. It is possible to install up to 4 hives on a stand (2 stacked pairs). In the case of 2 or more hives per stand, they should be placed with their flight holes facing opposite directions to minimize drift among the colonies.
•The hives must be fastened to the stand. In the absence of sugar water the hive becomes light and may sway or fall under strong wind.
•The hives should be placed in shady and well-ventilated spots within the orchard or adjacent to it. In any case, a shade should be attached above the hives to protect against both sun and rain.
•After placing the hive, let the colony inside “settle down”. After a few minutes, carefully open the flight-hole by lifting the shutter that blocks it. The bees will leave the hive immediately and commence their “orientation flight” which will later enable them to find their way back to the hive without difficulty. Soon thereafter the bumblebees will start visiting the cherry flowers.
•The activity of the bumblebees is most intensive during the morning and afternoon. The bumblebee can function under a wide range of temperatures (8-33°C), the optimal range being 15-25°C. Cloudiness or rain does not interfere with outdoor bumblebee activity.

Field advisory service
•The bumblebee does not leave a visual sign of visitation on the cherry flower.
•Follow-up of bumblebee activity and state of the hive should take place once every 10-14 days and should include two elements:
1) Observation of entries and exits of workers to and from the hive. In a normal colony, a minimum of 10 entries and exits can be observed within 10 minutes. Attention should be paid to the color of the pollen loads on the workers entering the hive. The color of pollen load from cherry flowers is light yellow.
2) Direct observations on bumblebee activity on the cherry trees.