Christopher -- ow! -- Robin," called out the cloud.

"Yes?"

"I have just been thinking, and I have come to a very important decision. These are the wrong sort of bees."

A.A. Milne, "Winnie-the-Pooh," 1926

Suspended among the treetops from a blue balloon and disguised as a rain cloud, Pooh got pretty close to his honeycomb goal before reporting the bad news to Christopher Robin that "the bees are now definitely Suspicious."

Suspicious, for bees, means ready to sting. And nowadays, many beekeepers in South and Central America are finding their bees Suspicious with a capital S. Indeed, some beekeepers have concluded, like Pooh, that theirs are flat-out "the wrong sort of bees."

In many cases, they are right.

The problem is African honeybees. These easily agitated, aggressively stinging insects have gradually spread northward since their introduction into South America in 1956. Swarming roughshod over the countryside, they've been taking over hives inhabited by the more docile local bees while stinging to death a few hundred people along the way.

Just how big a threat these bees pose to the U.S. beekeeping industry or to the general public is a matter of considerable debate.

Two weeks ago, after years of anticipation, some federal planning and a whole lot of handwringing, USDA scientists intercepted the first swarm of African bees to enter U.S. airspace. About 5,000 of the six-legged, short-fused bees flew low over the Mexican border near Weslaco, Tex., only to be betrayed by their olfactory instincts.

The swarm was lured into a USDA trap laced with a synthetic pheromone -- a chemical that swarming bees secrete when they agree upon their choice of a new home. Officials destroyed the swarm after microscopic analysis of the bees confirmed their African lineage.

With their killer reputations preceding them, the bees' arrival in the United States has stirred growing concern among entomologists, beekeepers and the public at large.

To assess the danger, insect geneticists have focused on a key question: To what extent are African honeybees interbreeding with the more easily managed New World honeybees that live in U.S. hives?

Initially, entomologists reckoned that the African bees' irritable demeanor might be diluted after sufficient hybridization with their American cousins, most of which derive from European ancestors. Those hopes dwindled last year with the publication of two reports that found little genetic evidence of such interbreeding.

At the same time, scientists speculated that perhaps the bees would become more easygoing in cooler climes.

But since then, new studies have hinted that some hybridization may indeed be happening and that cold temperatures may not bother the bees as had been supposed. Faced with conflicting data painting very different pictures of critical genetic trends, entomologists cannot reach a consensus on how to deal with the influx of expatriate insects.

Anxiety about the bees has been fueled by reports of the gruesome deaths of people who were attacked by furious swarms. But deaths resulting from mass stingings by African bees have become less common in recent years, especially in the insects' northern range. Stinging deaths have dropped from an average of 75 per year in Venezuela during the bees' first five years there to only eight deaths in Mexico since the bees crossed its border in 1985, says Thomas Rinderer of the USDA's honey bee research laboratory.

Those numbers probably reflect both a mellowing among African bees and an increased human effort to avoid antagonizing them, Rinderer says. He and others hypothesize that in temperate regions, the meanest tropical bees will find themselves at an ecological disadvantage. Hybrid bees will likely predominate and a hybrid zone, perhaps a few hundred miles wide, may ultimately stretch across the southern United States. A similar hybridization zone seems to exist in Argentina, he says, which may form a barrier to the fiercer African bees.

African bees will have an increasingly difficult time as they cross the border and move northward through the United States, says H. Glenn Hall, an entomologist with the University of Florida in Gainesville. But in parts of the American South, African bees "are probably going to become well established -- and they're going to cause a lot of problems," he says. It is likely, scientists say, that these problems will be related to agriculture, not health.

To cope with the influx of alien bees, USDA officials have introduced large numbers of European bees into Mexico, with hopes of enhancing hybridization rates. And in an effort to buy time while hybridization occurs, USDA researchers have deployed hundreds of bee traps in the countryside and human "hit squads" in some cities to capture and kill African swarms moving through Mexico.

While agency officials say their strategy slowed the insects' advance, Hall says they have little to show for their efforts.

Still, he says, "I'm not sure any effort would have worked. This is a major biological phenomenon. You're talking about trying to stop the tide with a bailing bucket."Escape of the Killer Queens

The tide began its rise in southern Brazil, where Italian honeybees, although appreciated for their good temperament, have proved to be poor honey producers. In 1956, Brazilian scientists imported 46 Southern African queen bees as part of a program to breed a better bee -- a placid but prolific producer well adapted to South American conditions. The program backfired when 26 queens escaped from the lab into the jungle. The rest is entomological history.

Three decades and 7,000 miles later, the progeny of the escapees have begun what is expected to be a major influx into the United States. Their arrival was well-documented. The closest colonies spent last winter about 150 miles south of Brownsville, Tex. With African swarms capable of migrating up to 100 miles at a stretch, U.S. entomologists expected them to enter U.S. territory earlier this year. But a hot, dry summer apparently delayed their arrival.

Nobody looked forward to the bees' arrival. But now that the first splashes of this entomological wave have hit U.S. shores, scientists will have a chance to answer one of their most pressing questions: What kind of bees, exactly, will these newcomers be?

"Originally, we anticipated there'd be a lot of interaction, and the African bees would pick up European traits," says Orley R. Taylor, an entomologist at the University of Kansas in Lawrence. But Taylor, working with Deborah Roan Smith and Wesley M. Brown of the University of Michigan at Ann Arbor, has conducted genetic studies indicating that African queens, compared with European queens, seem either genetically dominant or ecologically better suited to take advantage of neo-tropical niches.

The researchers examined mitochondrial DNA from 66 honeybee colonies in Brazil, Venezuela and Mexico. Since mitochondrial DNA is inherited only from the mother, analyzing it in captured workers provides an indication of the relative mating success of European and African queens. The team reported its surprising results in an issue of the journal Nature published last year: 97 percent of the workers tested positive for African mitochondrial DNA. The researchers concluded that "mitochondrial genomes of a small number of African females have rapidly colonized most of a continent."

In the same issue of Nature, Hall and K. Muralidharan of the University of Florida reported that all 19 wild swarms they captured and analyzed in Mexico had African mitochondrial DNA. The finding further clarified the nature of the African bees' expansion, showing that it has resulted mostly from African maternal lineages spreading as swarms, rather than from African drones inseminating European queens. Those two papers shocked entomologists and beekeepers in North America; no one had expected the African matriarchies to make their way so far north without a little more genetic mixing.

"It's very surprising that the African bees in Mexico do seem to be offspring of an unbroken chain of African bees," says P. Kirk Visscher, a bee geneticist at the University of California at Riverside. However, he adds, "just how much this really tells us, I don't know."

The problem, explains entomologist Robert E. Page of the University of California at Davis, is that population dynamics over continental expanses cannot be deduced from a few spotty studies at random locations. The Nature papers were "significant," Page says, but he calls the authors' interpretation "overstated."

For example, he says, in some parts of Central America and Mexico, African bees may have had very little contact with European bees, but significant contact and hybridization may be occurring in other areas. Moreover, bees with differing genetic backgrounds may show varying survival rates in particular environments. "There's no reason to think that what's going on with African bees should be uniform throughout their range," says entomologist Richard Nowogrodzki in Ithaca, N.Y.

In fact, recent studies by Walter S. Sheppard of the USDA's Agricultural Research Service in Beltsville and Rinderer of the USDA's honeybee research lab in Baton Rouge provide good evidence for interbreeding. In two studies -- one performed in Argentina and the other comparing honeybee species from around the world -- the researchers used mitochondrial DNA analyses to prove that African males in the wild have been mating and producing offspring with European females, and vice versa.

The finding counters a suggestion by Taylor that metabolic differences between European and African bees may be significant enough to prevent their respective DNAs from functioning well in combination. Says Rinderer: "We conclude that hybridization does occur to a large extent and there's no fundamental (genetic) incompatibility."

But Will They Survive?

Taylor argues that even if African and European bees do interbreed, the offspring -- or the offspring's offspring -- may not survive as well as those of purer African strains. "The pattern indicated that at first there's a puff of hybridization, then the {gene} frequencies drift back more toward African," he says. This suggests that the hybrids ultimately do not compete well in nature.

"The African bees seem to pick up European characteristics, then lose them because of natural selection, genetic dilution or lack of European input," Taylor concludes. In this way, the African bee seems to genetically "reconstitute itself," he says. Indeed, he adds, his studies of wild bees captured more than 400 miles north of Mexico's southern border -- in an area that has one of the highest concentrations of European hives in all of Mexico -- indicate that "they're showing more African traits than they did farther south."

Hall concurs. "In Venezuela, in Honduras, in Costa Rica, in Mexico, it's the same story," he says. "The evidence to me is indisputable. We conclude that European maternal lines aren't making it."

Scientists on both sides of the issue acknowledge they still know too little about bee genetics to back up some of their sweeping predictions. "The story is far more complex than we had anticipated," Taylor concedes.

The economics of an influx of African bees remain difficult to predict as well. Hall maintains that honey prices probably won't change, in part because much of the honey in the U.S. is imported from such places as China. "But the economics of pollination will escalate," he says. Managed bees are critical to agriculture in the U.S., where roving beekeepers transport their hives around the countryside to pollinate an estimated $10 billion worth of crops, such as almonds, melons, squash, apples, cherries, alfalfa, and other commodities each year.

If African bees start taking over hives in the South, and traveling beekeepers encounter increased hassles and costs in controlling their bees, "food prices will probably go way up," Hall predicts.

USDA scientists tend to downplay such dire scenarios. So far, they note, government brigades using hormone-drenched traps have captured and then killed more than 13,700 northward-moving African swarms in Mexico. Taylor and other critics say that number is minuscule compared with the more than 2 million managed hives in Mexico and the large, uncounted population of wild bees. But USDA officials maintain that the delaying tactic has worked, and they say the bees' impact in the U.S. will be greatly reduced with expanded trapping of intruding swarms, periodic introductions of European queens and mass releases of European drones.

Ultimately, everyone agrees, the final picture will depend on just how much hybridization really occurs, how well the hybrids will compete in temperate environments and how genetic intermingling affects bee behavior.

"It's obvious to me that hybridization is occurring in some transition zones," says USDA's Sheppard. That observation leads him to believe that the bees will not pose such an extreme problem by the time they become a permanent part of the U.S. landscape. "But am I right about that? I'll know in 25 years, at the end of my career."

Adapted with permission from SCIENCE NEWS, 1990 by Science Service, Inc.