Assessing possible ecological risks of genetically modified crops:
Genetic-monitoring of non-target organisms exposed to Bt corn

Michael Blum, Uwe Stolz, and Mark Bagley

Office of Research and Development, National Exposure Research Laboratory, Ecological Exposure Research Division



Emerging	Tec

Genetically modified (GM) crops have great potential to reduce our
dependence on chemical pesticides. One class of GfVI crops has been
engineered with a gene from the bacterium Bacillus thuringiensis (Bt) to
produce toxins that defend against a number of insect pests, including
European corn borer, tobacco budworm, and western corn rootworm.
While the EPA has taken great care to ensure that the Bt toxin does not
detrimentally affect the environment, the long-term risks of
incidental exposure to populations of untargeted insects and other
animals must continue to be monitored.

Genetic monitoring is a potentially powerful approach for assessing whether populations of
beneficial organisms, such as butterflies and honeybees, are affected by long-term exposure to
genetically modified crops. For example, analysis of gene expression levels using microarray
technology may provide more sensitive assays of sub-lethal exposure to the Bt toxin than current
methods. Analysis of variation in DMA sequences or molecular markers such as microsatellite DNA
may demonstrate whether genetic diversity and population genetic structure are affected.
Genetic monitoring of gene expression and molecular genetic diversity over time will help to
establish population trends that reflect ecosystem-level changes.

lophnio water fleas
(Water)

Nematodes

(Soil)

Assaying exposure and response of individuals to Bt toxins: Differential gene expression

A

Display of a microarray gene chip indicating
variable expression of different genes in
a single individual

Assaying exposure and response of populations to Bt toxins: Genetic diversity (DNA sequence
variability and variation at microsatellite DNA markers) within and among populations

Collembola
(Leaf Utter)

Introduction of genetically modified corn into an agroecosystem may expose a wide
range of organisms to Bt toxins. The depicted groups of non-target organisms have
been examined in previous studies of Bt toxin effects. Some groups (circled in red)
have been shown to respond to Bf toxin exposure.

Fluorescent microsatellite markers
visualized on an acrylamide gel indicating
genetic variation across individuals within
a population

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Farmering to Protect Human Health and the Environment

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