THROUGHOUT THIS spring’s battle over gypsy moth spraying in Seattle, the pro-spray forces hammered away at just one message: There is no scientific evidence that the anti-moth agent Bacillus thuringesis kauristaki can harm human beings and higher mammals.

There is plenty of evidence, on the other hand, that the microorganism Bacillus cereus is not harmless. B. cereus is a well-known cause of “food poisoning,” with symptoms ranging from headaches and diarrhea to vomiting and unconsciousness. B. anthracis is even worse: The anthrax bug multiplies in the blood of its victim— producing symptoms such as loss of motor control, bleeding, convulsions, and suffocation—and often kills its victim outright.

So what’s the connection? Just this: According to a group of Norwegian scientists who have been studying all three bacteria for over five years, they aren’t three different bugs but a single species. The different effects each has on its victims depend on the presence or absence of little loops of extrachromosomal DNA called plasmids.

Bacteria normally don’t go in for sex; they just keep budding off new copies of themselves, passing some of their characteristic plasmids along in the process. But under stressful conditions, bacteria do get sexy, cuddling up beside each other and exchanging genetic information—in the form of plasmids. In other words, all it would take for a “harmless” btk bug to become a blood-eating anthrax bug is a swapped plasmid or two.

Now, before you imagine you hear the whup-whup-whup of black helicopters coming to get you, be assured that there is no evidence that such a swap has ever taken place. But until the good folks in Professor Anne-Brit Kolst’s research group at the University of Oslo’s Department of Microbiology started looking into the matter, there was no evidence that it could take place either.

The authors of the study, which was recently published in the journal Applied Environmental Microbiology, go out of their way to avoid running up any red flags about btk, which is used all over the developed world to control moths destructive of commercially valuable crops. But their findings were striking enough to persuade the staid scientific journal Science—no friend of radical enviros—to highlight their study in its weekly survey of the cream of just-published research.

The citation in the June 16 issue of Science concludes “[I]t is known that all three Bacillus species are naturally able to take up plasmids. Indeed, plasmid exchange between B. cereus and B. anthracis has been verified experimentally. However, before sounding a general alarm, it cannot be ruled out that there is some other special, but as yet undetected, feature of the B. anthracis genome that makes it alone of the three species particularly adept at retrieving and retaining virulence plasmids.”

What do scientific and governmental authorities who have been telling the public that btk offers no risk to public health have to say about the Norwegian research? So far, two things, neither reassuring. “We’ve known for a long time about the close similarity between these microorganisms,” says the state health department’s John Kobayashi. “The question was raised before spraying began this year, but we were assured by the [federal] Centers for Disease Control that the CDC did not feel there was cause for public concern.” According to King County chief epidemiologist Jeff Duchin, the source of that comforting information was David Ashford, of the CDC’s Bacterial Disease Division in Atlanta. A copy of the Norwegian report was forwarded to Dr. Ashford soliciting his comments but had not borne fruit by press time. Nor had there been any response from a similar query to Vic Mastro, director of the Department of Agriculture’s Falmouth, Massachusetts, Plant Health and Technology Labs, the federal government’s top scientific advocate for the use of btk as an insecticide.

WHILE WE’RE WAITING to hear what state and federal gypsy moth experts have to say about the future of their program, we can pass the time reading about what it’s costing us. Active ground and aerial spraying for both European and Asian varieties is over for the year, but a spreadsheet made available by the state Department of Agriculture shows that the really pricey part of the program is just getting under way. Altogether, $1.7 million was allocated for fiscal 2000 for gypsy moth control, with the state picking up 55 percent of the tab and the federal government the rest. The $175,000 spent on spraying makes up less than 20 percent of the budget, compared to the $1 million plus set aside to cover the salaries and benefit packages of employees of the program, not to mention leasing and gassing the vehicles they use for “follow-up” surveys.

Anti-spray protesters often call attention to the role the economic interest of companies that manufacture btk sprays plays in keeping such programs going. Less often noted is another group with a financial interest in heavy-duty, high-investment control efforts: the state contractors and employees who carry these efforts out.

Unfortunately for the public interest, we depend on these same people for advice about whether such programs are economically viable and clinically safe. Even more unfortunately, our public health authorities depend on them too. Check out the King County Health Department’s Web page to inform the public about btk. After some helpful hints on what to do if you think you’ve come in contact with the spray, you’re told who to get in touch with if you think your health has been affected. The health department? No: “Call the Washington State Department of Agriculture Gypsy Moth Hotline at 1-800-443-6684.”

For more on moths, see Moth-eaten state.