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Sunflower Bee's a Great Pollinator!

A hard-working native bee can sometimes top the pollination prowess of the domesticated honey bee—even when badly outnumbered. "In our experiments using outdoor enclosures," says ARS entomologist Vincent J. Tepedino, "sunflower leafcutting bees spread out evenly among sunflowers instead of visiting just the plants nearest their nesting boxes."

Tepedino has affectionately nicknamed the bees "megapugs," short for Megachile pugnata. They're native to southern Canada and most of the United States except the lower Mississippi Valley and Gulf Coast.

Dark-colored and about 3/4- to 1-inch-long, the bee forages on sunflowers and other species in the sunflower family. It uses leaf pieces and moistened soil to make partitions between compartments, or cells, that house its young.

"Megapugs could be used wherever sunflowers are grown," Tepedino notes. "They are charming and dutiful. Every sunflower grower should have a bunch."

Tepedino used four 100-by-20-foot screened enclosures, owned by Pioneer Hi-Bred International, Inc., at Woodland, California, for the experiment. One kind of sunflower produced significantly larger and heavier seeds after being pollinated by the megapugs than when pollinated by domesticated honey bees, Apis mellifera.

The test was the first using sunflower leafcutting bees to pollinate hybrid sunflowers in field cages, says Tepedino. In earlier work, other ARS researchers at Logan, Utah—where Tepedino is based—scrutinized megapug performance in open fields. There, too, the bees were better than honey bees as outdoor pollinators of sunflowers.

In the new test, Tepedino enclosed bees within the four cages, each with about 600 sunflower plants inside. For around 2-1/2 weeks, about 100 sunflower bees in each of two cages performed pollination chores. Meanwhile, a few thousand domestic honey bees—over 10 times more than the megapugs—performed the same task in two other cages.

For one type of sunflower, there was no significant difference in the size of seeds harvested or the total seed weight per flower head. For the second kind of sunflower included in the experiment, however, those pollinated by the sunflower leafcutting bee produced seeds that were about 30 percent larger, on average, than seeds on plants pollinated by honey bees. Total seed weight per flower head was also about 30 percent greater.

Tepedino expects to have results of a follow-up study late this year or in early 2000.—By Marcia Wood, Agricultural Research Service Information Staff.

Vincent J. Tepedino is at the USDA-ARS Bee Biology and Systematics Laboratory, 5310 Old Main Hill, Logan, UT 84322; phone (435) 797-2559, fax (435) 797-0461.

"Sunflower Bee's a Great Pollinator!" was published in the September 1999 issue of Agricultural Research magazine.