Pollinator Strength

David Owens, Extension Entomologist; owensd@udel.edu and Gordon Johnson, Extension Vegetable & Fruit Specialist; gcjohn@udel.edu

Honeybees are used extensively to ensure adequate pollination for vine crop vegetables (cucurbits) and for many fruit crops (apples, berries, etc.). Without good pollination, poor fruit set or misshapen fruit can occur. Most of the honeybees used for pollination are rented from beekeepers. Questions have come up how to know if a colony is strong enough to provide adequate pollination service. A good resource on pollinators, colony strength, and farmer best management practices for pollinator health (including water sources can be found in the MidAtlantic Vegetable Production Recommendations, Section A, pages 21 – 27.

It is important to ensure having enough bees (managed and wild) to avoid having problems with fruit set and misshapen fruit. There are two ways to check the strength of a colony: in-hive inspection and assessing hive traffic at the entrance. In the hive, bees should cover 6 to 8 frames, have 4 to 6 frames of brood and (eggs, larvae, and capped) fill 1.5 to 2 boxes. This is considered a ‘minimum standard.’

An easier, but less accurate method of assessing colony strength is to watch colony entrances in late morning to early afternoon on a calm day. During a 1 minute interval, 50 – 100 bees should be arriving and leaving the colony. While counting bees, be sure to note the presence of bees carrying pollen. They will have large yellow ‘sacs’ on both back legs.

Farmers should work with their beekeeper to ensure that only strong colonies are placed in fields. This has become more difficult in recent years due to higher winter mortality caused by bee pests and pathogens. Stronger colonies provide much more pollination service than one or two weaker colonies. Beekeepers should work with the state apiarist, Meghan McConnell to assess colonies. On the farm side, farmers should read labels carefully and avoid making applications when bees are active in fields. Several insecticides and miticides have pollinator advisory language on them. The fastest way to find it is to download the label from a website such as cdms.net and search the label for ‘bee’ or ‘pollinator’ using Ctrl + F. Insecticides of special concern have a bee in a red diamond to indicate pollinator protection language. Bees can also be affected by fungicide applications. Bees feed their larvae fermenting pollen, and bees rely on the microbes living with them to fend off diseases; fungicides can disrupt the beneficial microbes in the colony. Thus, even fungicides should be timed for periods when bees are not active in the crop. On warm days, bees also forage for water to cool the colony. Having a clean water source within a ¼ mile will benefit the bees. This doesn’t necessarily mean flowing water; large puddles should suffice.