•Each avocado flower opens twice on two consecutive days:
1)In the first opening, the flower is functionally female; no pollen is released but the stigma is white and receptive to pollen. The style stands erect from the center of the flower; the corolla and the stamens lie at a right angle relative to the style. The nectaries are not active, but the stamenoids do secrete nectar .The flower then closes until the next day.
2)At the second opening, the flower is functionally male; pollen is released and the stigma starts to dry up and turn brown. The three inner stamens hide the style and stigma. The remaining six stamens are inclined at a 60 degree angle relative to the style.
 
Avocado cultivars are classified according to the time of the day they flower. Type A cultivars have female flowering in the morning of one day and male flowering in the afternoon of the next day. 'Haas' cultivar belongs to Type A group. Type B cultivars have female flowering in the afternoon of one day and male flowering in the morning of the next day. 'Etinger' and 'Fuerta' cultivars belong to Type B group. Due to the unique blossoming rhythm, a well-accepted practice is to interplant avocado orchards with varieties of opposite groups to promote cross-pollination.

Inadequate pollination is known as the main limiting factor of fruit-set in avocado in Israel. Honeybees are apparently insufficient pollinators. They prefer the competing citrus bloom and wild flowers to the avocado flowers, thus limiting the fruit-set of early cultivars like ‘Etinger’ and ‘Haas’. Furthermore, in the case of interplanted ‘Etinger’ and ‘Haas’ cultivars, the honeybees are ineffective in pollinating ‘Haas’ at a distance of more than a row or two from ‘Etinger’. Since ‘Haas’ is highly dependent on cross-pollination, it represents another limiting factor on the yield of this variety.

•The bumblebee has been proven 10 times more effective than the honeybee for within-cultivar pollination and 20 times more effective at pollination between cultivars. The foraging habits of the bumblebee differ from that of the honeybee. Whereas the honeybee foragers follow the signs of the "patrol" group of foragers for new/alternative sources of pollen and/or nectar, the bumblebee workers forage individually. Therefore, bumblebees from hives placed in the orchard are likely to visit the avocado bloom at a relatively higher rate than honeybees, especially when competitive bloom is present. An additional advantage of the bumblebees is that they are active at relatively low temperatures, on cloudy and rainy days, conditions typical of the intermediate season when the avocado blooms and in which the honeybees will not leave the hive.

•A field trial carried out in conventional orchards in Israel for 5 consecutive seasons showed that pollination of avocado with bumblebees added to honeybees, increased the yield of ‘Etinger’ cultivar by 24% and that of ‘Haas’ by 15% compared to honeybee pollination alone. In a bio-organic orchard a 51% increase in total yield was recorded for ‘Haas’.

The hive
•When it leaves the factory, the standard bumblebee colony for avocado consists of the founder queen, about 50 workers and a few dozen young developmental stages (eggs, larvae and pupae). Under optimal conditions the colony develops and reaches its peak activity 2 weeks after introduction. This activity continues for at least 4 weeks. Thus the hive provides effective pollination for ca. 6-8 weeks.

•The bumblebee hive is introduced to the field with an initial amount of sugar water that serves as a substitute and/or supplement for the natural nectar in the avocado flowers. The sugar water lasts about 7-10 days. Thereafter the colony is strong enough to continue developing without additional sugar water. This situation stimulates intensive nectar foraging in addition to pollen foraging.

Introduction scheme
•The recommended introduction rate is 6-7 bumblebee hives per ha. in addition to honeybees at a minimal rate of 3-4 hives per ha.
•For 'Etinger' and 'Haas' interplanting, the bumblebee hives will be placed at three intervals: the first one at the start of 'Etinger' bloom (about 5% blossom), the second one at the peak of 'Etinger' bloom and the beginning of 'Haas' bloom, and the third one at the peak of 'Haas' bloom.
•This gradual introduction will ensure adequate pollination throughout the entire blooming period. Honeybee hives should be introduced simultaneously with the bumblebee hives.

Placement of the hive in the field
•The bumblebee hives are placed in groups of 4 (2 stacked pairs) on a vertical stand specifically designed for this purpose. The hives should be placed with their flight hole facing opposite directions to minimize drift among the colonies.
•The hives should be fastened to the stand.
•Once the sugar water is depleted, the hive becomes light and may sway or fall under strong wind.
•The hives should be placed under the tree canopy in order to avoid exposure to direct sunlight. When placing the hives one should also consider avoiding damage by mechanical equipment and minimize the chance of getting wet by adjacent sprinklers. In any case, a shade should be attached above each quadruplet to protect against both sun and rain.
•The minimal distance between bumblebee hives and honeybee hives should be 30m.

Field advisory service
•A Bio-Bee field advisor should be present at each introduction of hives in the field.
•Checking bumblebee activity will be carried out both on the trees and next to the hive's flight hole.
•Checking for the presence of bumblebees on the trees requires certain expertise. A trained field advisor will do it.
•Assessing bee activity at the hive's flight hole is easier and can be done by the grower as well as by the field advisor.
•In a normal hive, a minimum total of 5 entrances and exits should be observed within a 5-minute period.
•This examination should take place under reasonable weather conditions, i.e. neither rain nor extreme heat. In cases where sufficient activity is doubtful, the examination should be repeated.

Bumblebees and plant protection
•In Israel, no pesticides are being used during the pollination period in avocado. However, in case there is a need to use pesticides during the pollination period, the grower should consult Bio-Bee’s updated list of side effects of pesticides on the bumblebees.