National Geographic : 2005 Mar
prompted domestication of the cat-but it's one with a rather mixed record. A moth aptly named Cactoblastiscactorum tamed 16 million acres of prickly pear cactus infesting the Australian out back. But a weevil introduced to subdue inva sive musk thistle in the U.S. is clobbering native thistles. Research and testing of biocontrol agents are extremely expensive. And even effective bio controls rarely accomplish the job on their own. The flea beetles used to combat spurge, for example, are no magic bullet. They don't work in sandy soil, they don't perform in cool weather, and they can take years-as many as ten-to reduce really bad infestations. The best approach, experts say, is integrated pest management (IPM), combining, in this case, sheep and bugs and herbicides where needed. In North Dakota, research is showing that IPM has an added advantage: grazing two or more species, sheep and cattle, for instance, and managing the amount of time each spends on a given patch of land, increases the biodiversity of the grasses and improves soil, strengthening the land's abil ity to resist invaders. It's too soon to declare victory, but for the first time in almost a century, spurge in North Dakota is on the wane. Integrated pest management is a good approach to controlling established invaders, Jim Carlton says. But better yet is "integrated vector man agement-preventing invasives by managing every footstep of the pathway that brings a spe cies from Brazil to France or from Hong Kong to San Diego. People always ask me, 'Hasn't everything that can be introduced already been introduced?'" Carlton says. "Well, there's a European fouling invertebrate called a sea squirt, Ascidiella aspersa,that's probably been on the hull of thousands of European ships over 500 years of shipping. But it only showed up for the first time in a New England bay in the 1980s. Based on that time line, I'd say no: Everything that can invade has not invaded, and we can't afford to let it." 116 NATIONAL GEOGRAPHIC * MARCH 2005 It will take worldwide political action to tackle the problem of invasives, Lodge and others believe. They suggest that the new, more strin gent security measures being instituted in the U.S. to prevent terrorist activity offer an oppor tunity. Invasive species control measures could be piggybacked onto them. Military experts might welcome such collaboration. A 2004 article in Parameters,the U.S. Army War Col lege quarterly, warns that terrorists could use in vasives as weapons to "disrupt and demoralize the U.S. government and its citizens over time." Individual action is needed too. "Roll up your sleeves and get out there," urges Dan Simberloff of Tennessee University. Many people have. Leahi Santos, 5, has her nonindigenous Cayuga ducks in a row-ready to feast on the invasive gold en apple snails that infest her family's taro crop. Although the ducks are the family's most effective weapon against the snails, Hawaii no longer allows Cayuga importation fearing that they may themselves become inva sive, interbreeding with or displacing native ducks (justas the exotic plants along this path have over whelmed native plants). So taro farms may soon join the casualties of man kind's urge to tinker with nature's balance.