practices and the loss of (semi)natural habitat types, field margins have become increasingly
important habitats for conserving biodiversity (ERA step 1).Riskis defined as a function of
the adverse effect (hazardorconsequence) and the likelihood of this effect occurring
(exposure). For butterfly species the potential hazard is the toxicity of pollen containing
Bt protein, and the likelihood of the event is the environmental exposure of caterpillars
to the pollen (ERA step 2). Laboratory studies show that monarch butterfly caterpillars
that consume Bt maize pollen from the transgenic event Bt 176 had higher mortality,
slower development, and lower pupae weights than did those fed non-Bt control pollen
(ERA step 3). This result caused a great deal of angst, which was accompanied by media
and regulatory attention. This case shows that extrapolation of laboratory data to field scen-
arios can be quite controversial; this case has been among the most (if notthemost) contro-
versial of all from GM plants. Laboratory tests provide information on toxicity and fitness
parameters, but they often represent “worst-case scenarios,” which do not reflect field con-
ditions or population processes that operate over farming landscapes. For example, maybe
under tier 1 tests caterpillars were force-fed too much pollen compared with realisitic field
exposures. Therefore, adverse effects identified in laboratory studies must be verified
under field conditions because spatial, temporal, and environmental factors can alter possible
adverse effects from, for example, exposure to the Bt protein or temporal overlap
between pollen shed and phenology of butterfly caterpillar. One experimental exposure to
Bt protein study under field conditions was performed by the authors of this chapter in
Germany. In a database survey it was shown that approximately 7% of the German butterflies
(macrolepidoptera species) occur mainly in farmland areas where maize is grown [for further
reading on how this was done, see Schmitz et al. 2003]. The case study summarized below
addresses some of the issues discussed above. In particular, this study attempted to compare
the effect(s) (if any) of Bt maize on nontarget lepidopteran larvae, with that of conventional
insecticides. The suitability and efficacy of the experimental designs and methods used for
ERA were also evaluated. It is important that proper comparisons and control treatments
be used in ERA experiments to ensure that results are relevant to real agriculture. Since
most farmers would spray insecticide instead of simply letting insects eat their entire crop,
it is important that ERA for insect resistant transgenic plants such as Bt maize include com-
parisons using chemical insecticides, since this is what most farmers use to control damaging
insects. There are a few researchers who would like to use, as the main baseline, idyllic con-
ditions that do not exist in much of real agriculture, but that would not be a fair, realistic, or
useful comparison.
13.3.1 Effect of Bt Maize Pollen on Nontarget Caterpillars
An experimental maize field in Germany was studied over a 3-year period from 2001 to
- The field was divided into plots about 0.25 ha in size surrounded by a strip of
conventionally grown corn with a minimum of 4.5 m in width (Fig. 13.1). There were 24
plots in total, on which corn was cultivated in three different ways (or in more precise ter-
minology,treatments). The maize treatments were used in a randomized pattern to avoid
side effects from the surrounding environment. A conventional variety, “Nobilis” with a
similar genetic background but no transgene was used. Recall from Chapter 3 that this is
callednear-isogenic. ISO (O for control) was the control treatment using the near isogenic
plant with no insecticide spray. This treatment provided a baseline for any assessment of
effects. In the second treatment the near-isogenic variety was sprayed with the chemical
insecticide Baytroid (this treatment is abbreviated INS), which simulated classical pest
13.3 AN EXAMPLE RISK ASSESSMENT: THE CASE OF Bt MAIZE 315