Hive ventilation system improves summer bumblebee activity

26/07/2021 - Since the 1990s, Bombus terrestris bumblebees have been used to pollinate tomato crops grown on the south-eastern Iberian Peninsula.

During this time, Biobest has greatly improved the quality and design of its commercial bumblebee hives. However, occasionally issues can still arise with tomato pollination - predominantly due to adverse environmental factors.

Challenges

Although now rare, problems can arise following the application of plant protection products that are incompatible with bumblebees - which negatively impacts on colony development. Also, greenhouse plastics that filter out UV light below 400mm can make it challenging for bumblebee workers to see, leading to reduced hive active. Ants in the crop can also negatively impact colony development. Coming in search of the sugar solution at the base of the hive, they can disturb bumblebees and their juvenile stages.

However, the main crop pollination issues are usually associated with adverse microclimatic conditions in the crop that affect both the bumblebees and tomato plants.

Extreme heat

In summer, bumblebee activity is reduced by extreme heat. At temperatures above 30°C, bumblebees spend time ventilating the hive during the middle of the day. Reducing their activity in the crop, they tend to only emerge in search of pollen in the early morning and late afternoon.

It is therefore essential to keep hives as well ventilated as possible by placing them in cool places in the greenhouse. However, this alone is sometimes insufficient. To improve the situation, Biobest has developed a passive ventilation system for its hive that improves the flow of hot air inside the colony, especially in summer months.

Passive ventilation system

Air enters through slots at the bottom of the hive, rises and is expelled through the top - creating a chimney effect. This ventilation system improves the performance and useful life of the hive under high-temperature conditions.

Biobest hive with passive ventilation system

Field trial

To evaluate Biobest’s passive hive ventilation system, a 10,000 m² greenhouse producing Camelot cherry tomatoes was selected in Níjar (Almería). The trial took place over four weeks - from late August to late September.

In an area close to the ventilation band in the crop, hives were placed in three experimental blocks with each ventilation system either open or closed.

As the graph shows, during the trial the highest bumblebee activity was recorded for hives with open ventilation. These results were reflected in the external appearance of the hive.

Flight activity of bumblebee workers over four weeks

Those with the highest bumblebee flight activity were heavily stained around the exit opening (See images below.) 

  
Hive with closed ventilation                                           Hive with open ventilation showing higher activity - entrance more stained

Practical recommendations for summer hive use  

As we have seen, Biobest’s specially designed passive ventilation system improves bumblebee activity during the hotter periods of the year. This higher activity can be translated into better colony development (more durability in the crop) as well as more effective pollination.

In addition to opening the hive ventilation system, it is essential to place the hive in the coolest area - next to the greenhouse ventilation band, in the shade and in the lower part of the crop - in order to facilitate the entry of air into the hive.

Biobest also recommends placing the hive on top of a box and protecting it from ants - which are usually more active during the hottest periods of the year.