www.czu.cz ; www.raupp.info

Why it's OK for transgenic plants and animals to spread. "GE Grass Spreads
Genetic Pollution over Large Distances" warns the headline in the
environmentalist magazine Grist last month. Pollen from a grass genetically
modified for herbicide tolerance was found 13 miles from where it was
planted. Biotechnology foes have always warned us that genetically modified
creatures, once free in the outside world, are beyond our control, October
2004 by Ronald Bailey.

For example, the Sierra Club worries, "These organisms cannot be
recalled?they will continue to pass on their spliced-in genes, or
transgenes, to future generations. Many of the gene changes may turn out to
have unexpected secondary effects. Serious errors in judgment might prove
unrecallable as trillions of copies are broadcast via pollen and seed."
Sounds ominous, right? However, that genetically modified organisms released
into the wild might be unrecallable is not necessarily a knock-down argument
against them. After all, lots of unmodified organisms are unrecallable too.

Most transgenics so far allowed outdoors are crop plants genetically
enhanced to resist insects and diseases, and to tolerate herbicides. Crop
plants have been modified through millennia by farmers so that they simply
cannot survive in the wild. You won't see corn plants taking over forests or
swamps. Nevertheless, some genetically modified crop plants have crossbred
with wild relatives. But so do conventional crops. Norman Ellstrand, a
genetics professor at the University of California at Riverside notes that
"there is now substantial evidence that at least 44 cultivated plants mate
with one or more wild relatives somewhere in the world...crop-to-wild gene
flow is not uncommon, and on occasion, it has caused problems. Would we
expect transgenic plants to behave any differently? The answer is 'no.'"

Critics often worry that genes for herbicide resistance from genetically
modified crops can flow into weed species, making them more difficult to
control. However, this is hardly a novel problem. As professor of plant
physiology Jodie Holt, also from Riverside, observes, "As use of herbicides
has increased, increased cases of selection for resistance in weeds have
been documented. Since the first reported case of weed resistance in 1970,
258 weed species have evolved resistance to one or more of 18 herbicide
classes." Despite the fact that for nearly a decade millions of acres have
been sown with biotech crops, there have been precious few outbreaks of the
much-dreaded "superweeds" caused by crossbreeding between biotech crops and
wild plants.

So now some scientists are working on deliberately releasing genetically
modified organisms above the plant level into the wild. For example,
mosquitoes have been genetically modified so that they can no longer harbor
disease-causing organisms, such as the malaria parasite, or viral diseases
such as dengue fever and yellow fever. The tropical kissing bugs in Central
and South America have been infected with genetically engineered bacteria
that kill the Chagas trypanosome parasite that the bugs carry. The
trypanosome carried by tsetse flies in Africa that causes sleeping sickness
might be controlled in a similar fashion.

Researchers at the University of California at Riverside are trying to stop
an epidemic of Pierce's disease that is threatening California's vineyards.
The disease bacterium is spread by a leafhopper pest called the
glassy-winged sharpshooter. The Riverside scientists have modified another
bacterium that lives in the guts of the sharpshooters so that they kill the
bacteria that cause Pierce's disease. Other researchers are trying to modify
honeybees to resist the diseases and parasites that have devastated huge
numbers of hives in the past decade.

This kind of genetic engineering approach is an extension of biological
control strategies already in regular use. For example, pink bollworm moths
that attack cotton, as well as screwworm flies that infest livestock, are
controlled using Sterile Insect Technique (SIT). Male moths and flies made
sterile through irradiation are released in huge numbers so that they will
out-compete their wild rivals for mating with wild females, whose eggs then
produce no progeny. The U.S. Forest Service controls gypsy moth infestations
by spraying forests with a preparation of a natural virus that infects and
kills only gypsy moths.

Unlike crop plants, which can't typically compete with wild species,
researchers hope that genetically modified insect species will successfully
out-compete unmodified wild members of their species. Any potential negative
effects will have to be balanced against the benefits expected?which can be
substantial. For example, at least 300 million people contract malaria and
nearly three million people die from it every year. Using interbreeding to
replace wild populations of malaria-carrying mosquitoes with mosquitoes
genetically modified to resist malaria would be a tremendous boon to
humanity.

This process of releasing genetically modified insects and microorganisms to
control diseases and pests will undoubtedly be modeled on successful
programs like the biological control of the weed purple loosestrife.
Biologists imported and released two leaf-feeding beetles and a root-eating
weevil from Europe that eat only purple loosestrife. These insects were
tested in laboratories before they were released to make sure they would not
endanger native North American plants. This effort at biological control has
significantly reduced stands of the weed. In a similar fashion, future
genetically modified insects will be extensively tested and monitored in the
lab before they are released, to minimize any ill effects.

While it is possible that genetically modified plants and animals could
become disruptive when introduced into the wild, this risk must be evaluated
in light of what we know about the history of introducing unmodified new
species into ecosystems. In the 500 years since Columbus arrived in America,
some 50,000 foreign species have become established in North America. These
include nearly all our major crop plants: wheat, oats, soybeans, apples,
oranges, and pears; and our livestock: cows, pigs, goats, sheep, and horses.
Of course, some destructive pests have also found their way to our shores,
but for the most part introduced species have not been particularly
disruptive and have integrated well into our landscapes.

A recent study on the ecological effects of genetically modified trees by
researchers at Oregon State University noted, "Invasive exotic organisms
represent the coordinated interaction and evolution of thousands of genes in
a new environment, usually devoid of its pests and pathogen complex,
[whereas] transgenic organisms result from one or a few intensively studied
genes that encode highly specific traits."

It is reasonable to expect that creatures like insects modified with just
one or two well characterized genes will be less disruptive than introduced
exotic species, since their wild relatives will already be living in the
ecosystem into which the modified animals are being introduced. If
mosquitoes genetically modified to resist malaria or West Nile virus
actually succeeded in replacing wild carriers, people would suffer just as
many irritating bites from the bloodsucking nuisances. But they'd come down
with fewer cases of illness. And returning to transgenic grasses,
biotechnologists have now genetically modified popular lawn and pasture
grasses so that they lack two common hay-fever allergens. Not even the
Sierra Club should sneeze at such positive results.

Ronald Bailey is Reason's science correspondent. His new book, Liberation
Biology: A Moral and Scientific Defense of the Biotech Revolution will be
published in early 2005.

[www.reason.com]

------------------------------------------
Posted to Phorum via PhorumMail