Even when outnumbered 10 to 1, hardworking sunflower leafcutting bees sometimes do a better job of pollinating sunflowers than domesticated honey bees. There is renewed interest in alternative pollinators because many commercial honey bee hives have been hard hit by varroa and tracheal mites. The sunflower leafcutting bee is Megachile pugnata. ARS researchers conducted the experiments in outdoor enclosures. Pioneer Hi-Bred International, Inc., at Woodland, CA, provided the four 100- by- 20-foot screened enclosures. Each held about 600 sunflower plants. For about 2-1/2 weeks, about 100 sunflower bees in each of 2 cages performed pollination chores. A few thousand domestic honey bees—about 10 times more than the sunflower leafcutting bees—performed the same task in 2 other cages. For one type of sunflower, seed size and total seed weight per flower head were about the same, regardless of which bees did the pollinating. For the second kind of sunflower, pollination by the sunflower leafcutting bee produced about a 30-percent increase in seed size and total seed weight per flower. Results of a follow-up test should be ready later this year or in early 2000.

Bee Biology and Systematics Laboratory, Logan, UT
Vincent J. Tepedino, (435) 797-2559, andrena@cc.usu.edu

Scientists have discovered a new clue to a mostly mysterious process: How do molecules called phytochromes switch on genes to command a plant to respond to sunlight? Plants use phytochromes to sense sunlight. Phytochrome-sensitive genes may trigger many responses such as flowering or making sugar for energy from sunlight, air and water. The scientists, based at the ARS/University of California Plant Gene Expression Center, determined that a kind of phytochrome known as phytochrome B, when activated by sunlight, will bind to a protein called PIF3—a previously unknown step. Phytochrome B doesn't bind if it is kept in the dark, according to the researchers' lab tests. The phytochrome investigations may eventually lead to new ways to change when and how plants respond to sunlight. This could speed development of genetically engineered plants that, for example, germinate or flower at times controlled by growers. New clues about how phytochrome B interacts with PIF3 to control genes should serve as a helpful new model of how other signaling pathways might work, such as those that control genes for resistance to drought or insects.

ARS/University of California at Berkeley Plant Gene Expression Center, Albany, CA
Peter H. Quail, (510) 559-5900, quail@nature.berkeley.edu