In Nature Vs. Nature, Nature May Not Win

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Subject: In Nature Vs. Nature, Nature May Not Win

      By GINA MARANTO
      
     S everal weeks ago, when 170 Michigan schoolchildren were infected
     with hepatitis A after eating tainted strawberries imported from
     Mexico, the nation wondered what other viruses and bacteria might
     be hitching a ride across the border on foodstuffs.
     
     Microorganisms, it turns out, are but a tiny part of a growing
     problem. Every day hordes of foreign insects, plants, and animals
     infiltrate the United States.
     
     There are 500 million plants flowing into the United States each
     year -- about 80 percent through the Port of Miami -- and tons of
     fresh fruit, vegetables and grains where alien insects can hide
     out. In Florida alone, state biologists have tallied some 1,300
     established alien plant species, some of which have despoiled
     uncounted acres.
     
     Today the scale of the international traffic in flora and fauna is
     so vast -- and the resulting hazards to agriculture and ecosystems
     potentially so great -- that there is a whole branch of science
     devoted to the militaristic sounding study of "invasion biology."
     
     How, then, should one react to the news that scientists, in an
     attempt to deal with what are variously called aliens, immigrants,
     xenophytes or, simply, introduced species, are opting to bring in
     still more exotic species? Isn't this foolhardy?
     
     For example, the U.S. Department of Agriculture is about to do a
     controlled release of the snout beetle near Loxahatchie to try to
     get rid of the Australian melaleuca, a tree which is spreading
     across the Everglades at a rate of about 35 acres a day, forming
     dense thickets that crowd out native plants. The snout beetle, also
     known as the melaleuca weevil, is one of the most tested bugs in
     history, so it probably won't wind up eating mahogany or palms
     instead of melaleuca.
     
     But the snout beetle isn't the only foreign bug that is being
     drafted to gobble up a pest. Researchers in Gainesville, Fla., have
     finished up Brazilian field tests of a parasitic fly, the phorid
     fly, that can kill non-native fire ants, which have decamped in 11
     southern states, by laying eggs upon the ants' bodies. The
     researchers hope to do outdoor tests in Gainesville this summer and
     then to turn the flies loose in nature. Spectacular Goofs
     
     This strategy, known as biological control -- fighting nature with
     nature -- has had some spectacular failures. Take the cane toad.
     Imported by Australia in the 1930s to oblige sugar cane growers --
     against the dire advice of a naturalist named Walter W. Froggatt --
     the poisonous cane toad was meant to get rid of a beetle that was
     devastating the sugar cane crops.
     
     However, explains herpetologist Walter Meshaka, Jr., supervisory
     curator at the Everglades Museum, "Beetles fly at night and were
     inaccessible to the toads." So the voracious toads ate everything
     else, having a field day in an under-exploited niche. Soon 102
     toads turned into a trillion.
     
     Or think of that staple of ecology textbooks, the Indian mongoose,
     which Hawaii imported to eat rats that were overrunning cane
     fields. Between 1883 and 1885, the mammals were brought in, leading
     not only to a small drop in the rat population but to the
     destruction of ground-nesting native birds throughout the islands.
     
     Then there was Kudzu. Although not technically a biocontrol agent,
     this Japanese plant was planted across the American South during
     the 1930s as an erosion buster; it now blankets whole landscapes,
     ruining native habitats.
     
     Or recall the arrival of tilapia, a fish meant to take care of
     hydrilla, a runaway exotic aquatic plant that clogs Florida
     waterways: The tilapia didn't make a major dent in the problem they
     were supposed to solve but they did manage to drive out native
     fish, especially large-mouth bass, the prime freshwater sport fish.
     
     It is cases like these that make ecologists frown on using
     vertebrates and amphibians as controls.
     
     Yet there have been successes, cases where insects imported to take
     care of a runaway colleague or an invasive plant have done their
     work, with limited impact on other species. Parasitic wasps have
     proved helpful in California's orchards. Beetles from Europe and
     northern African have pushed Klamath weed out of some 5 million
     acres of rangeland in the West. In the South, flea beetles have
     thwarted alien alligator weed.
     
     Peter Room, an entomologist at the Center for Tropical Pest
     Management in Brisbane, Australia, has had successes all over the
     world with a Brazilian beetle. First he cleared 500 acres in Lake
     Moondarra of a free-floating aquatic species called Salvinia
     molesta. Then, he introduced the beetle to Sri Lanka, India,
     Zambia, Kenya, Fiji and Malaysia.
     
     When the costs and benefits of the Sri Lanka project were tallied,
     the return for every $1 spent was $53, and farmers were saved 1,673
     hours of clearing salvinia for every hour of work by scientists.
     
     It's no wonder that in the 1960s, biological controls were touted
     as the "green" alternative to pesticides and herbicides. But now
     the supporters of biocontrols are duking it out with skeptical
     ecologists over what "success" and "safety" really mean.
     
     And some former supporters of biological controls, notably Daniel
     Simberloff, a biologist at Florida State University, have changed
     their minds. Mr. Simberloff suggests that the impact of biocontrols
     on natural systems has not been adequately assessed and they should
     be a last resort.
     
     Of course, as the ecologists are battling it out, exotic species
     that are not part of any controlled program are coming to our
     shores every day, with the possibility of wreaking havoc. In its
     1993 report the Office of Technology Assessment said the nation
     spends at least hundreds of millions of dollars each year to
     extirpate exotic species that endanger native species or threaten
     agriculture.
     
     Biocontrols are, naturally, also subject to the law of unintended
     consequences. Even though scientists may know a fair amount about
     an ecosystem, they can never predict with complete accuracy what
     will happen when they release a new exotic species.
     
     But after all is said and done, taking a considered risk may be
     better than sitting around while the invading hordes run riot.