Agriculture Forum: Solitary bees play pollinator role


Well, spring just might be here at last. It was been a long wait for temperatures like we have seen this week. This should finally push along the development of our region’s crops, forests and landscape plants.

Warmer temperatures will also increase the numbers and activity of many species of insects. Some of these will be unwelcome pests, but fortunately, a lot of them will be pollinators, eager to visit the blossoms of our crops.

The first pollinator insect that comes to mind is usually the honey bee. Hives of honey bees can contain many thousands of bees, and they can easily transported to where they are needed for pollination. Certainly, agriculture and home produce gardeners rely on this important species for a great deal of crop pollination — but it is not the only important pollinator in our area.

There are more than 450 species of bees in Michigan. None of these other bees live in large colonies, and very few of them can be easily transported to where they are needed. Despite these limitations they are still very important pollinators.

Bumble bees account for about 20 species of the bees in the state. Most bumble bees live in small colonies, consisting of a queen and 20 to 40 worker bees at the peak of the season. In the fall of the year, new queens are produced by the colony. The workers all perish at the end of the season and only the queens survive the winter. This means that at the start of spring, every bumble bee you see is a queen, and they are all trying to establish a new colony. Bumble bees often nest in the ground, often in an abandoned animal burrow. Some companies offer cultured colonies of bumble bees for pollination services.

Most of the other bees in Michigan are “solitary,” meaning that they do not live in colonies.

Individual female bees do all of the work of forming nests and collecting food. Three-quarters of the state’s solitary bees nest in the ground; they excavate tunnels and small brood chambers in which they store a mixture of pollen and nectar. A single egg is laid in each chamber, then the nest is sealed up and the bee grubs that hatch from the eggs feed on the stored food. The adult bees have a relatively short period of activity, perhaps only a few weeks to a month — then they die of old age. The development of the next generation of adult bees usually takes until the next growing season.

Most of the rest of Michigan’s solitary bees are “cavity nesting” species; these use pre-existing cavities or holes in trees and other objects for their nest sites. The adult bees typically use mud or small pieces of leaves to line the cavity and form separate brood chambers. The rest of their behavior and life history is like that of the ground-nesting solitary bees. Commercially sold “bee hotels” are designed to provide nest sites for this group of bees.

Cherry bloom will be coming along soon. If the weather is relatively warm and the winds are light, honey bees will be very active and the primary pollinator in the orchards.

However, if the weather is cool or a little windy, the solitary bees will become more important, as they are more tolerant of poor weather conditions. We can keep hoping for nice weather, but it is good to know that the solitary bees are ready to fly and be our MVPs (most valuable pollinators) for the cherry crop.

Erwin “Duke” Elsner is a small fruit and consumer horticulture educator for the Grand Traverse County MSU Extension.