Unintended harm to other organisms:
a laboratory study was published in Nature (scientific magazine) showing that
pollen from B.t. corn caused high mortality rates in monarch butterfly
caterpillars. Monarch caterpillars consume milkweed plants, not corn, but the
fear is that if pollen from B.t. corn is blown by the wind onto milkweed plants
in neighboring fields, the caterpillars could eat the pollen and perish.
Although the Nature study was not conducted under natural field conditions, the
results seemed to support this viewpoint. Unfortunately, B.t. toxins kill many
species of insect larvae indiscriminately; it is not possible to design a B.t.
toxin that would only kill crop-damaging pests and remain harmless to all other
insects. This study is being reexamined by the USDA, the U.S. Environmental
Protection Agency (EPA) and other non-government research groups, and
preliminary data from new studies suggests that the original study may have been
flawed. This topic is the subject of acrimonious debate, and both sides of the
argument are defending their data vigorously. Currently, there is no agreement
about the results of these studies, and the potential risk of harm to non-target
organisms will need to be evaluated further.
effectiveness of pesticides:
some populations of mosquitoes developed resistance to the now-banned pesticide
DDT, many people are concerned that insects will become resistant to B.t. or
other crops that have been genetically-modified to produce their own pesticides.
transfer to non-target species:
concern is that crop plants engineered for herbicide tolerance and weeds will
cross-breed, resulting in the transfer of the herbicide resistance genes from
the crops into the weeds. These "superweeds" would then be herbicide tolerant as
well. Other introduced genes may cross over into non-modified crops planted next
to GM crops. The
possibility of interbreeding is shown by the defense of farmers against lawsuits
filed by Monsanto. The company has filed patent infringement lawsuits against
farmers who may have harvested GM crops. Monsanto claims that the farmers
obtained Monsanto-licensed GM seeds from an unknown source and did not pay
royalties to Monsanto. The farmers claim that their unmodified crops were
cross-pollinated from someone else's GM crops planted a field or two away. More
investigation is needed to resolve this issue.
several possible solutions to the three problems mentioned above. Genes are
exchanged between plants via pollen. Two ways to ensure that non-target species
will not receive introduced genes from GM plants are to create GM plants that
are male sterile (do not produce pollen) or to modify the GM plant so that the
pollen does not contain the introduced gene. Cross-pollination would not occur,
and if harmless insects such as monarch caterpillars were to eat pollen from GM
plants, the caterpillars would survive.
possible solution is to create buffer zones around fields of GM crops. For
example, non-GM corn would be planted to surround a field of B.t. GM corn, and
the non-GM corn would not be harvested. Beneficial or harmless insects would
have a refuge in the non-GM corn, and insect pests could be allowed to destroy
the non-GM corn and would not develop resistance to B.t. pesticides. Gene
transfer to weeds and other crops would not occur because the wind-blown pollen
would not travel beyond the buffer zone. Estimates of the necessary width of
buffer zones range from 6 meters to 30 meters or more. This planting method may
not be feasible if too much acreage is required for the buffer zones.