PUSH is finally coming to shove for the Africanized honey bee.In its three-decade expansion outward from the jungles of Brazil, the Africanized honey bee encountered relatively small populations of bees with which to compete. But with its drive into northern Mexico and its arrival in Texas last fall, the Africanized honey bee has run headlong into established populations of European honey bees. Nature will select the winner. "We're dealing in a whole new arena here," says Thomas Rinderer, a geneticist specializing in bees. "The selection pressures are not the same." If the Africanized honey bee takes over commercially kept hives, the economic consequences could be enormous. Honey bees pollinate $20 billion worth of crops that directly or indirectly account for one-third of the United States diet. In Texas, beekeepers rent 17,000 hives to farmers to pollinate vast fields of melons and vegetables and huge citrus orchards. Africanized honey bees would be more difficult and expensive to manage for this purpose. The US also produces honey and other bee products valued at $200 million. Some of this could be impaired by the undesirable behavioral characteristics of Africanized honey bees. The high cost to mitigate these characteristics could drive many beekeepers out of business. The risk to public health from feral colonies of Africanized bees, though believed to be small, will be the largest concern of many people. Africanized honey bees have the same kind of venom as European bees, though less of it. But if the bees are provoked, the colony will inflict up to 10 times as many stings. Texas officials worry that the state tourism, worth over $17 billion, will suffer if people stay away. One thing is certain: "We cannot eradicate the bee," says Elba Quintero. As manager for the Africanized Honey Bee Program at the Department of Agriculture's Animal and Plant Health Inspection Service, Ms. Quintero is in charge of educating the public in south Texas about their new neighbor. Less than 400 years ago, European colonists brought the Western Hemisphere its first honey bees, which were called "white man's flies" by the Indians. So well adapted were these insects to North America's climate that a thriving feral population was soon established. Bees expanded westward faster than new colonists did. The European honey bee, accustomed to four predictable seasons and to finding food in the same place as the previous year, developed a preference for staying put and storing honey for the winter months. Beekeepers in the United States have encouraged those traits - and gentleness - through genetic selection. EUROPEAN bees never flourished in the monoseasonal tropics, where plants might produce the most nectar when daylight was shortest, in contrast to the cycle in the European bee's home latitudes. That's why African bees, which have a different strategy, were brought to Brazil as an experiment. These bees came from the Transvaal, a province of South Africa that has long droughts interrupted by unpredictable rainfall. The African bees deal with that by reproducing rapidly when there is food. The new swarms fly off in search of favorable conditions, and those that find them survive. Although they produce more than European bees, there's little storing of honey; it's all fed to the young. The bees defend their hive vigorously. But when the weather turns dry and starvation threatens, the original swarm will abscond - abandon its home in search of a better one. Scientists know that commercial hives can be kept populated with bees that are largely European by killing the queen and replacing it with a fully European one each year. But this process will be costly. Leon Praetorius, head of the Texas Honey Bee Identification Lab at Texas A&M University in College Station, Texas, points out that the more aggressive Africanized honey bee drones will shove a European honey bee aside in order to mate with the queen. So far, where Africanized and European honey bee populations have mingled, the offspring eventually revert to Africanized characteristics. But that took place in the tropics, where natural selection favored the Africanized honey bees. "The African bee may be different in south Texas than way down in South America," says Paul Jackson, chief apiary inspector for the Texas Agricultural Experiment Station. "Climate and stuff like this may make it react differently. We don't know for sure." Dr. Rinderer, who directs the Agricultural Research Service's Honeybee Breeding, Genetics, and Physiology Laboratory at Baton Rouge, La., warns against trying to predict natural selection. "The bee that's best adapted to that area [will dominate]. Unless that area is exactly Africa, the African-type genes are not necessarily the ones that are going to be selected." Texas is more like Europe than it is like Africa, he adds. "We know pretty much that they're going to go just about everywhere [in Texas]," adds Merry Makela, a geneticist with the Texas Agricultural Experiment Station who is working on a computer model to predict the course of the Africanized honey bee invasion. She says they will reach San Antonio by next spring, and swarms could even show up in Houston. "Whether they survive equally well all over the state of Texas is something we don't know," she adds. Judging by the areas of South America where the Africanized honey bee hasn't penetrated, it cannot survive long winters, Dr. Makela says. "There is a stable transition zone where Africanized honey bees and European honey bees are surviving at equal rates," Makela says. "Somewhere in the United States there is this hypothetical transition zone above which they cannot survive the winter." Scientists have varied widely in drawing that line. Some give only south Texas to the Africanized honey bees, others the southern third of the US, and others even Chicago and Boston. Meanwhile, 12 counties in south Texas have been placed under quarantine, meaning that beekeepers are not allowed to move hives out of those counties. "We don't want man to spread it," Mr. Jackson says. "The quarantine is not going to stop the [Africanized] bee," he adds, but "it will slow it down, let it start interbreeding. That's one of the main goals for it." THE spread of the Africanized honey bee is being monitored through traplines that extend for hundreds of miles across south Texas. Once the bees break the line, the quarantine area will be extended. Bees caught in the traps have to be dissected and measured to determine if they are Africanized or not. This procedure takes several hours and requires at least 10 bees, Mr. Praetorius says. If the average length of the right forewing is 10 millimeters or longer, the sample is not Africanized, he says. If it is shorter, then another 27 measurements must be taken from the left fore and hind wings, the right rear leg, and the third abdominal plate. A program called USDA-ID records the digitized measurements, compares the sample to thousands of others on file, and calculates the probability that it is Africanized, European, or mostly one with evidence of introgression of some of the other genes . HOW THE AFRICANIZED HONEY BEE SPREAD African bees were brought to Brazil in 1957 as an experiment. When 26 queens accidentally escaped, they mated with feral European bees to create the Africanized honey bee. The expanding population has been moving north at 200 to 300 miles per year. Now Africanized honey bees have reached Texas, and scientists are wondering how far they will go and whether their defensiveness and tendency to abscond can be bred out of them.