Bumble bee Troubleshooting

Most of the time our customers have good results with bumble bees, but to help you in those times when there are difficulties here is a trouble shooting checklist.

Sometimes growers feel that their bees are not working properly, when the markings seen on the flowers are very light. As long as a flower has been visited, and marked, no matter how light the markings are, the flower will have set. The best indication of the activity of a hive is not from how many bees you see working, or how many bees are in the hive, compared to how many flowers are open, but from the percentage of marked flowers you can see in the house. When using hives supplied by Zonda Beneficials, it is best to use the following guidelines:

House Size
Under 750m2 Small Hive
Between 750-1100m2 Medium Hive
Between 1100-1500m2 Large Hive

Hives should be replaced every 4 weeks, or if your house is larger than 2000m2, new hives should be introduced more frequently.

Over the summer months, markings may be much fainter. This is due to the fact that the pollen is very ripe and the bee has only to touch the flower for the pollen to fall onto it.

The number of bees working the flowers will always be a minority of the total bees in the hives, and is mainly affected by the amount of brood and the strength of the queen. You should expect to have about one bee foraging per 300 plants, or 100sq metres.

Comparisons between hives:

Bumble bee hives are quite variable and for smaller houses (less than 1000sqm) many of our hives are “over-strength”. So if you find one hive is less active than another it does not mean it is too weak for the job. You should use the level of flower marking as your judgement guide.

First, always check – Are the flowers marked?

There should be marks on the oldest flower in each truss. It does not matter whether the marks are faint or dark. If there is consistent marking you do not have a bee problem, even if you do not see much activity (one bee can visit about 300 plants).

If there is no adequate flower marking there can be many causes:

Bees may be attracted outside the greenhouse to other flowers.

This can be recognised by the hive being quite busy but returning foragers have pollen on their legs of various bright or dark colours and not the yellowy-white of tomato pollen. This may be a difficult habit to break. The best remedy to try is to use the ‘Bee Home’ to shut the bees inside the hive for most of the day. You can either let them out for 1 or 2 hours in late morning when the pollen flow from the flowers is greatest, or if possible with manual vents let them out in the late afternoon after you have closed the vents (or early morning before the vents open). When the bees are prevented from flying like this they develop a strong desire to forage when the opportunity comes and should be very busy during the ‘open’ period.

The flowers are not attractive to the bees.

This is often part of the same problem as above i.e bees go outside instead of foraging in the greenhouse. It can happen at low temperatures, high humidities or very high temperatures. It is difficult to give figures for these quantities because they are affected by the pattern over the course of a day, light levels, plant variety etc.

The hive is active but the bees will not fly.

Foraging for pollen is stimulated by larval brood (to whom it is fed) and a dominate queen. If the queen dies or larval brood is damaged (for example by rough handling during transport) foraging may stop. Foraging may also be reduced in dull weather especially under some twin-skin plastic coverings. A hive which seems strong but won’t fly should be returned to Zonda for an exchange.

The hive is too weak.

All hives eventually stop producing new workers and rear males (drones) and often queens instead. It is like “going to seed”, and is impossible to predict how soon this will happen. After this change the workers gradually die off and the males and queens fly away. Sometimes a hive can die out because the workers are visiting flowers contaminated with insecticide or they can be caught in spider webs. Get a replacement hive as soon as possible.

Misset can also be caused by several reasons:

  • Temperature
  • Light Level
  • Plant Balance
  • Humidity
  • Fertilisation
  • Pollution


When the temperature goes under 14 degrees some plants will stop setting. The germination of the pollen is too slow. Also at temperatures over 30 degrees setting maybe poor.

Light level

Very much temperature related. The temperature can be easily too high when the light level is very low. The difference is that at a direct high temperature (>30c) the pollen does not germinate, but with a temperature level which is relative to high compared to the light level the pollen does germinate but the plant does not have the energy to maintain the just set fruit. In the winter/early spring this can be easily the case.

Plant balance

Very vigorous crops, especially as long as they are not fully loaded with fruit , can cause problems with setting.Again there is no problem with the germinating of the pollen but the plant does not dedicate enough sugars to the fruit, sending them mostly to the vegetative parts. High run offs can indicate a watery plant.

VD2 is comparable to:

Temperature (◦C) RH %
15-17 80%
18-23 85%

VD7 is comparable to:

Temperature (◦C) RH %
15-18 50%
19-20 55%
21-22 60%
23-24 65%
25-26 70%
27-28 75%
29-30 80%


Lack of Boron will cause flower and fruit drop in very early stage. Also unbalance in fertilisation can cause problems. This should be checked by slab or soil analysis.


There are several polluters which can cause problems with mis-setting:

  • herbicides used in neighbourhood
  • acidity caused by CO2 gas due to bad working of burners. CO2 goes with H20 to form H2C03 =acid
  • acidity caused by wrong fertilizer (releasing ammonium gas)
  • nitrous oxide problems due to bad working of burners