In order to assure effective pollination by bumblebees during the cold season, it is essential to enlighten a few aspects related to the tomato plant and its response to low temperatures and hence stress the implications on the bumblebees.

In general, temperatures below 10°C do affect the process of fruit-set in the tomato plant. The specific effect depends on the tomato variety.

Pollen formation and development 
• Night temperatures of 6-7°C for 4-5 consecutive days, two weeks prior to anthesis, may significantly harm pollen viability even if day temperatures reach 20°C. During winter, when pollen count drops to an average of 60,000 grains per flower, the bumblebee is still capable of contributing significantly to the rate of fruit-set. However, if the amount of pollen drops to 40,000 grains per flower or less, Bombus activity (even at its best) cannot guarantee proper fruit-set.

Pollination 
• High relative humidity, above 90%, that accumulates in the greenhouse during winter, creates difficulty in pollen release due to the fact that the pollen gets clumped and thus is difficult to be treated by the bumblebees.

Pollen germination 
• Germination of the pollen grains is seriously hampered at temperatures below 5°C.

Growth of the pollen tube
• Temperatures below 10°C considerably slow down the growth rate of the pollen tube to the extent that it will not bring to fertilization, i.e. successful penetration of the ovule. Even short periods of low temperatures (a few hours) may have a negative effect on development of the pollen tube. Relative humidity between 50% to 90% enhances growth rate of the pollen tube.

Fertilization 
• At 10°C it takes the pollen tube ca. 84 hours to grow down to and penetrate the ovule.

Fruit formation
• Night temperature of 12°C in non-heated structures brings to formation of pointed and unevenly-shaped tomato fruits due to inappropriate development of the ovule and lack of placenta, seeds and the dense gelatin substance in one or a few of the fruit's lobes.

Pollination services
• It is essential to follow the visitation marks of the bumblebees in the closed flowers even under the most extreme cold conditions. It should be emphasized that the bumblebees are not responsible to pollen formation in the flower, therefore in the case of the pollen count dropping to less than a minimum of 40,000 pollen grains per flower, even the best performance of the bumblebees will not result in a proper fruit set. 
• Hormones can be applied as a backup to pollination under extreme and continuous cold conditions. Since hormones affect the female organs in the flower, it will not interfere with the bumblebee activity.
•  It is desirable to keep the temperature in the greenhouse constantly above 10°C, using every possible tool available to the grower. 
• High relative humidity in the greenhouse (=dense fog and condensation) must be avoided as much as possible. This will ease pollen release and will render the buzz-pollination by the bumblebees more effective. 
• Hives should not be placed under dripping gutters in the greenhouse. Water that is dripping continuously on the hive may shorten its life span. On the other hand it is crucial to place the hive at the most ventilated spot in the greenhouse.