Identifying and conserving bees in Michigan blueberry fields
Julianna Tuell and Rufus Isaacs
Entomology

Honeybees are by far the most economically important bees in our blueberry fields, and most growers know what these bees look like. However, there are many of other types of bees native to Michigan who nest in the soil and in cavities in old plants. This article provides some tips on identifying these “other” bees and some guidelines on how to improve the landscape in and around your farm to provide some help to build their abundance.

During bloom, the majority of bees on blueberry flowers are honeybees brought into the farm in hives. You may have also noticed bumblebees and some smaller bees on your flowers and wondered what type of bees these are.

In Table 1, we have provided a list of the different types of bees found on blueberry blooms, their common names, and the ecology of these different groups. In recent sampling of blueberry fields, we found that around 30 percent of bees were non-managed bees such as the Halictid and Andrenid bees shown in the pictures. The rest of the bees were honeybees. While this may not be a high proportion, many native bees are highly efficient pollinators of blueberry (which is a native plant). This is because they will forage at lower temperatures than honeybees, many will provide efficient transfer of pollen through buzz-pollination, they have a high rate of flower visitation, and they stay focused on blueberry flowers. Because of these factors, the overall influence of native bees may be greater than simply counting their numbers on bushes may suggest.

With this community of native bees visiting blueberry flowers and helping achieve pollination, it makes sense to consider easy approaches to help make blueberry farms more hospitable to these bees. Some basic approaches that growers can consider include providing flowering plants for bees to collect nectar and pollen from. To avoid overlap with blueberry bloom, the plants to select would be those that bloom early in the year such as willow, cherry etc., or plants that bloom after blueberry. Aggressive use of herbicides around the edge of fields are likely to prevent flowering plants from growing and will make the field less likely to have native bees. Because many native bees do not fly far, flowering plants should be provided in close proximity to fields, in the perimeter regions.

In addition to food, native bees need a place to live. Most of the native bees we have found in blueberry fields (miner bees, sweat bees, bumble bees) make their nests in the ground (Figure 1), with species aggregating their individual nests together in suitable areas. Providing areas of open ground or mounds of soil that are well-drained near fields can provide places for them to nest. We have seen bee nests in the weed-free strip under blueberry bushes and in bare areas of soil near fields. The adult native bees fly in and out of these nests many times during the year, collecting pollen to feed to their young developing larvae in the nest.

Some of the bees we have found visiting blueberry flowers are active only during the short window of time around blueberry bloom. For these species, minimal use of pesticide will be critical for their ability to emerge, survive long enough to lay eggs, and provision their nests. Other species are active through the season (e.g. bumblebees), and these species will require suitable resources throughout the season to sustain and build their abundance.

In summary, there are some simple practices that growers can adopt in and around their blueberry fields to enhance their suitability for native bees. It may take many years for populations of native bees to build, but enhancing native bees will provide a more diverse strategy for helping achieve high levels of pollination every year.