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Most of Missouri's native bees are thriving

Coneflower bee, Andrena helianthiformis.
Mike Arduser | Missouri Department of Conservation

This article first appeared in the St. Louis Beacon: If you visit one of Missouri’s native prairies when the coneflowers are blooming, you will see plenty of bees buzzing around them. You may not realize that some of these bees are a single species that collects pollen only from the pale purple coneflower and only on native prairie. This coneflower specialist flies for just a few weeks each year, collecting the pollen to feed its offspring until the coneflower blooms again.

Photo by Mike Arduser, Missouri Department of Conservation Coneflower bee, Andrena helianthiformis.

The coneflower bee, like the roughly 450 other bee species native to this area, seems to be doing OK. With a few important exceptions, according to Missouri Department of Conservation naturalist Mike Arduser, the native bee pollinators have been holding their own.  Arduser has been keeping track of bee diversity in the Midwest for about 30 years. 

Native bees — and there are about 3,500 species across the United States — have evolved to pollinate native plants. Some, like the coneflower bee, collect pollen from one specific group of plants, Echinacea. Some, like the squash bee, have slightly broader tastes and pollinate members of a single family like pumpkin or squashOthers, like the many varieties of sweat bees, are generalists and will visit almost any plant.

Bees are most important pollinators

Pollination by an insect is the only way that many of our foods can be propagated. As Arduser points out, each seed in a pumpkin or watermelon is the product of fertilization by one individual pollen grain. All those seeds show that the flower was visited many times by pollinators.

The so-called "pollinator crisis" does not refer to native bees. That very real economic problem concerns the honeybee Apis mellifera, which was imported from Europe in colonial times for beeswax and honey. No honeybees are native to this country.

"Colony collapse syndrome" is the condition in which honeybees leave the hive and do not return. Its causes are not clear. It may be pesticides. It may be the parasitic Varroa mite that came to this country in the 1980s. It may be the population density in hives used for today’s large scale agriculture. Or it may be a combination of all three or even a factor yet to be discovered.

Nonetheless, commercially raised honeybees are an economic necessity for pollinating large orchards and fields. The local Theis Farms uses commercial honeybees. Almond growers in California, whose orchards can be 10,000 acres, rely on truckloads of hives that migrate from location to location during the blooming season. 

Native bees have different lifestyle

Those honeybee hives, with their thousands of worker bees (up to 50,000 bees in a hive), and their ability to store food for the hive to survive the winter are not replicated by native bees. Their lives and habits are as different as a Wall Street financier’s and that of a subsistence farmer in sub-Saharan Africa.

Entrance to the nest of a ground-nesting bee
Credit Mike Arduser | Missouri Department of Conservation
Entrance to the nest of a ground-nesting bee

Native bees live for only one season.  Many of them nest underground, in solitary nests created by a single female. The coneflower bee is one such solitary bee. The newly hatched males and females emerge in the late spring and mate, which is the end of the line for the male. The female starts feeding and collecting coneflower pollen, as she builds her nest at least a foot deep in the ground. Each nest has 6-8 cells that she packs with pollen. She lays an egg in each cell, and then she dies. The larvae hatch in the early summer, feed on the stored pollen and emerge to mate just when the coneflowers are in bloom the following summer.

Two years ago, spring unexpectedly came to the Midwest weeks earlier than usual. Flowers bloomed weeks before their usual schedule. Yet the tiny bee that specifically pollinates one of the first flowers of spring — spring beauty— emerged synchronously with its pollen supplier, as did the coneflower bee a couple of months later. (Spring beauty pollen is pink, so that these bees often look pink.) Nobody has an explanation for the timing yet, says Arduser, but there is a sense that some underground signals are received by both the plants and their animal partners.

Many of the prairie specialists like the coneflower bee will not buzz around the coneflowers in your garden or in restored prairies like that in Forest Park. The reason may be that their flying ranges are limited and they have not yet discovered new sources of pollen. It may be that relatively undisturbed and unplowed soil in native habitats differs somewhat from heavily worked urban soil.

“Clearly there is a lot more to an animal’s life history than what they eat,” Arduser said. Ecologists have not yet discovered all the factors necessary to recreate a natural environment.

Not all native bees nest underground. About 15 percent nest in hollow twigs, holes in rocks, blackberry canes and other natural cavities. One of these, the blue orchard bee, is now being used commercially to pollinate orchards as an alternative to the honeybee. Only 250-300 females will pollinate an acre of orchard as they collect the fruit pollen for their nests. They tend to stay close to home, and orchard “bee condos” can be bought or made inexpensively. 

Native bumblebees are dwindling

The important exception to the overall health of Midwestern native bees is Bombus pennsylvanicus, one of six native bumblebees. Bumblebees are generalists, pollinating many kinds of plants during their summer lives. Because of their size, and because their numbers increase during the summer, they require large areas from which to collect pollen. Bumblebees mate during the fall, and the impregnated future queens go into solitary confinement insulated from the winter cold. In the spring, the queen emerges and establishes a colony.

Sydney Cameron, professor of entomology at the University of Illinois, and her colleagues have been studying bumblebees across the country.  Tracking eight common bumblebees, they have found that Bombus pennsylvanicus and three closely related species have suffered drastic losses, while four other bumblebees from a different sub-genera are thriving.

Bumblebee queen (Bombus auricomus) visiting Delphinium in the Ozarks
Credit Danny Brown | Missouri Department of Conservation
Bumblebee queen (Bombus auricomus) visiting Delphinium in the Ozarks

Bumblebees, like honeybees, are vital to  modern food production. Certain plants, like tomatoes and blueberries, depend upon bumblebees to "vibrate" their pollen loose. Honeybees can’t perform this vibration.

Growing tomatoes is a multi-billion dollar industry. Growers have come to depend upon commercial sources of bumblebees to pollinate the plants in their greenhouses. The bumblebee die-off began shortly after growers started importing bumblebees from Europe. Scientists hypothesize that these bees brought with them a fungal intestinal parasite, Nosema bombi. Cameron found that in all declining populations, the occurrence of the gut fungus was very high, 12 to 30 percent, as contrasted to 2 to 4 percent in nature. The correlation is striking, but it does not prove that the fungus is the basic cause of the decline. As with honeybees, pesticides, parasites, habitat loss or population density may be the primary cause and may make those species especially susceptible to the fungus.

Bees that do not pollinate

A surprising number of native bees do not collect their own pollen. These “cuckoo” or parasitic bees take over another bee's nest and lay their eggs in the cells prepacked with pollen. The cuckoo larvae hatch earlier than the host larvae and eat the stored pollen. Cuckoo bees sip nectar to fortify themselves so they can scout for good nests to conquer. They may inadvertently transfer some pollen as they sip, but they are not equipped to collect pollen. Many look like wasps. In Missouri, about 100 of the 450 species of native bees are parasitic.

Difference between bees and wasps

The short answer is that bees are vegetarian, and wasps are carnivores or omnivores. Both imbibe some nectar for energy, but bees require pollen as the only source of protein for feeding their young. Wasps are predators and scavengers.

You cannot tell by looking if an insect is a bee or a wasp. There are fuzzy wasps and naked bees, not to mention flies that look like bees. Nature is full of mimicry.

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