Contents - Faperta

342 Biotechnological Approaches for Pest Management and Ecological Sustainability
FIGURE 11.1 Detection of Bt toxins in arthropods in transgenic cotton under fi eld conditions using ELISA.
High levels of Bt toxin were detected in ash weevil (cell numbers 10 and 24) and grasshoppers (23 and 30);
while low levels of Bt toxins were detected in spiders (2 and 20), leafhoppers (4 and 26), green bug (5), red
cotton bug (8), larvae of tobacco caterpillar (11), and dusky cotton bug (21). 41 = Positive control. 42 = Negative
control. 43 = Blank.
insensitive insect species, and higher trophic level insects such as natural enemies. Such
information is important in the ecological context, particularly with the deployment of
transgenic plants expressing high levels of Bt-toxins constitutively.
Interaction of Transgenic Crops with Nontarget Organisms: Protocols for
Ecotoxicological Evaluation of Transgenic Plants
Ecologically, risk is the result of exposure hazard, which is a function of concentration,
exposure time, and distribution. In the case of Bt-insecticides, the toxins are applied topically,
whereas the toxins are expressed constitutively in all plant parts in the transgenic
plants, albeit at different concentrations. Therefore, in addition to the chewing type of
insects, the sap sucking and tissue boring insects are also exposed to the toxin proteins.
The Bt-insecticides degrade rapidly in the fi eld due to UV light, and their persistence in the
environment is low (Behle, McCurie, and Shasha, 1997). However, constitutive expression
of Bt toxins in transgenic plants exposes the insects to the toxin proteins throughout the
life cycle, and across generations. Extended temporal and spatial expression results in
greater exposure, and possibly may present a greater risk. As a result, all insects colonizing
a crop during the growing season may ingest some amount of toxin proteins, a proportion
of which may pass on to the natural enemies in the processed form.
Therefore, there is a need to standardize the protocols for ecotoxicological testing of
transgenic plants on nontarget organisms, including higher trophic level organisms. Such
studies need to take into account the novel and extended route of exposure caused by constitutive
expression of the toxin protein in transgenic plants. The protocols should include