Killer bees boost coffee yields. (Agriculture).

Coffee plants are self-pollinating, so they fruit and set seed without the help of pollinating insects. What do you get when bees nevertheless come by the coffee grove and do their thing? Bonanza yields, according to a new report.

David W. Roubik of the Smithsonian Tropical Research Institute in Balboa, Panama, knew that coffee blooms get a lot of traffic from pollinating insects. Since the early 1980s, most of the winged visitors there have been Africanized honeybees. To probe their impact on coffee growing, Roubik monitored berry yields from blooms pollinated with and without the help of bees. Each fruit has two seeds, better known as coffee beans.

Roubik put fine-mesh bags over some branches of flowering blooms on 2-year-old, shade-grown Coffea arabica shrubs. Other branches remained available to insects. Though a bloom lasts only about a day, each unbagged flower was visited on average by about 40 Africanized honeybees. Because these easily irritated bees have a tendency to form stinging swarms, they're often called killer bees.

Some 50 percent more berries reached maturity on flowers pollinated by bees, compared with self-pollinated flowers, and each of the mature beans was about 7 percent larger if bees were involved.

The bottom line, Roubik reports in the June 13 Nature, is that insect pollination boosted overall bean yields by 58 percent. Although Panama's native bees--mostly small, stingless varieties--helped coffee growers a little, Roubik says their virtual replacement by Africanized bees has begun stabilizing coffee yields in the country at near-optimal levels.

The findings emphasize the value of farming coffee in shaded environments. Not only does it allow for use of high-quality but sun-shy C. arabica plants, Roubik notes, but the free pollination services of native and Africanized bees are only available because of the presence of nesting hollows in nearby large trees.--J. R.