- The flower of carrot (Daucus carota) is hermaphroditic and self-pollinating.
- As the stamens in each flower and umbel ripen a few days earlier than do the pistils, cross-pollination occurs more often than self-pollination.
- The flower produces nectar as well as pollen.
- It is difficult to see whether the flower has been visited by bumble bees.
- The nectar produced by the carrot flower is not always sufficient for the optimal development of the colony. For this reason sugar water is supplied.
- The pollen production of the carrot flower is also insufficient for the development of a bumble bee population. Pollen is accordingly supplied with the hive, with which the bumble bees must be fed daily.
- For pollination of carrot, N colonies are normally used. On delivery, an N colony consists of 50 to 60 worker bees. The colony has an expected life span of 8 to 12 weeks.
- The approximate pollination range per hive is 500 m². For smaller areas, another type of hive may be suggested by your consultant.
- Place the hive 0.5 to 1 meter above the ground, in a place that is protected against sun and condensation/rainwater. During the winter period, placement in the sun may be desirable. Do not place the hive among foliage!
- Cut off any CO2 supply in the immediate vicinity of the hive.
- Secure the hive so that ants cannot enter it.
- After placement of the hive, let the bumble bees settle down for a while (½ - 1 hour) before opening the flight hole.
- If the crop is located in glasshouses or tunnels, open the flight hole of the hive when the ventilation windows are closed (at the end of the afternoon). This will prevent the bumble bees from going outside the glasshouse during their orientation flights and not returning to the hive.
- Following their initial orientation flights the bumble bees will immediately start pollinating the crop.
- In general, bumble bees are most active in the morning and in the afternoon. Their activity also depends on the flowering pattern of the crop.
- Bumble bees are active at temperatures between 10 and 30 degrees Celsius. They function best at temperatures between 15 and 25 degrees Celsius.
- Combining the use of bumble bees with natural enemies does not present any problems.
- Agricultural chemicals may have direct or indirect effects on the bumble bees. Direct effects occur when worker bees and larvae die as a result of contact with or digestion of a chemical product, and indirect effects occur when the smell of the treated flower puts off the bumble bees, causing visits to stop.
- Systemic pesticides (pesticides that are absorbed through the roots) often have a long-lasting residual effect. If a flower produces nectar in addition to pollen (e.g. sweet pepper), the damage to the bumble bee population may be much more serious than in a crop that only produces pollen (e.g. tomato).
- You will find detailed information about persistence and compatibility of pesticides with bumblebees and most other beneficials in Koppert's Side Effects Database On-line.
- In all cases the BEEHOME option of the hive must be activated before the crop is treated. This option ensures that bumble bees can enter, but not leave the hive. After about an hour the hive can be closed completely, so that it can either be covered or removed from the greenhouse.
- If the hive is temporarily removed from the greenhouse, it should be stored at 18 to 20 degrees Celsius.