Election Section

UC Study Counts Albany, Berkeley Bee Population

By JOE EATON Special to the Planet
Tuesday March 30, 2004

Listening to biologists could easily lead you to believe that all field work has to cope with impassible roads, extreme weather, tropical diseases, leeches, guerilla movements, or some combination of the above. I remember the late herpetologist, Joe Slowinski, describing how everyone in his party contracted malaria in Burma, then going on about what a great place it was in which to work. (On his next trip back, Slowinski was fatally bitten by one of his research subjects.) 

So I was pleased to learn of a recent study by a team of entomologists that entailed nothing more risky or strenuous than walking the residential streets of Berkeley and Albany, counting bees and flowers. 

Robbin Thorp, an emeritus professor at UC Davis, and his colleagues were looking for patterns of native bee diversity in urban settings. Since we’re talking about artificial habitats filled with flowering plants from all over the world, and since many native bee species are specialists in only one or a few kinds of flower, you might not expect much in the way of variety. 

But you’d be wrong. As reported in Fremontia, the journal of the California Native Plant Society, the bee counters found 74 species in their study area. All but two—the ubiquitous honeybee and a European leafcutter bee—were natives. That’s not much compared with a bee hotspot like Pinnacles National Monument with its 398 species, but it’s not bad for next door. The natives were common visitors to native shrubs like ceanothus and California poppies, but they also patronized cosmos, marigolds, marguerites, and other exotics. 

Bee diversity peaked at two locations, the Peralta Community Gardens and the Oxford Tract. With large numbers of bee-attractive plants packed in close proximity, each drew about 20 species of native bees. It probably helped that both gardens were pesticide-free. 

We tend to think of the honeybee as the typical bee, but in fact its social lifestyle is unusual. The hive habit evolved only a few times, in honeybees, bumblebees, sweat bees, and some tropical groups. The vast majority of bee species are solitary. 

If you’ve noticed a non-honeybee in your garden, odds are it was a bumblebee—maybe the yellow-faced bumblebee, which has the resounding Latin name of Bombus vosnesenskii. Their colonies are annual, like those of wasps; the workers die off in fall, leaving the queen to hibernate through the winter and found a new realm when spring comes. 

In some parts of northern California up to a dozen bumblebee species may coexist in a small area, partitioning the floral resources. Species with tongues of different lengths feed at flowers with nectaries of different depths. But some short-tongued bumblebees cheat by biting into the base of a flower to get at the nectar, bypassing the pollen-bearing parts. 

Among the solitaries, the leafcutter bees are the most conspicuous. Males will stake out a patch of flowers and patrol it for females. You’re more likely to see the work of the females, though: neat semicircular cuts excised from the leaves of your rosebushes with the bee’s scissor-like jaws. 

The leafcutter’s nest can be in almost any crevice or cranny, including hollow plant stems and beetle tunnels in wood, garden hoses, even the radiators of abandoned cars. She lines it with elongated leaf fragments, pads it with oval pieces, provisions it with pollen and honey, lays a single egg, seals the brood cell with a plug of circular leaf bits, and moves on. Leafcutter bees will also use artificial nests with ready-made holes, and that European species, the alfalfa leafcutter, has become a commercially important pollinator. 

Mason bees—here’s one species in Berkeley—have their own variation: using resin from pines and other trees, mud, and chewed-up plant material to construct their brood cells. These were favorites of the pioneering French entolomologist Jean-Henri Fabre. 

Fifteen of the bee species recorded in the Berkeley-Albany study were miner bees in the genus Andrena, which has 150 species in California alone and over 500 in North America. As the name implies, they dig their nests, usually in the form of a straight shaft with brood chambers branching off it. The excavation is usually two feet deep or less, but one Colombian miner bee is known to tunnel more than eight feet down. 

What’s remarkable about andrenid miner bees is the way they line their brood cells to keep out the dampness of the soil. They’ve evolved a biological equivalent of polyester. Female miners have an organ called the Dufour’s gland which secretes a sticky substance that the bee spreads over the cell wall. The stuff dries to a waxy or varnish-like finish, effectively watertight and fungus-proof. The chemistry varies: andrenids use a mix of terpenes, others produce polymerized lactones. 

The authors of the Berkeley bee study didn’t have an historic baseline to work from, but they report anecdotal evidence that honeybee numbers have decreased in the last 10 years or so. Since honeybee populations all over North America have been hard hit by parasitic mites, the local decline makes sense. It’s a good thing for home gardeners that the bumblebees, leafcutters, masons, and miners were still around to take up the slack.