because of exposure. Bt Cry1Ac endotoxin will kill monarch larvae and certain other larvae
if there is enough of it. The job of risk assessment is to determinerelevantexposures and
hazards.
13.4 Proof of Safety versus Proof of Hazard
A proof of safety (¼equivalence) between Bt maize and the near-isogenic variety was
performed using a two-sided (1–2a) confidence test (learn more about this approach by
reading Chow and Shao 2002). The percentage change of abundance is easier to interpret
than the species-specific absolute difference of arthropods. Therefore, confidence intervals
for Bt/ISO ratios were estimated. A ratio.1 for a taxon is equivalent to anx-fold increase
in abundance in the treatment; a ratio,1 is equivalent to a decrease in abundance in the
treatment down tox%. According to the risk assessment objective, the demonstration of
no meaningful change for selected nontarget species in Bt maize relative to the near-
isogenic variety should be proven. The nontarget species can be considered as not mean-
ingfully changed, if the lower and upper limits of the confidence interval for the abundance
ratio are close to and encompass the value 1. Otherwise, the compared treatments cannot be
seen as being “equivalent.” Abundances can vary in all three treatments; therefore, the
confidence intervals for the ratios INS/ISO and Bt/INS were also estimated.
13.5 Proof of Benefits: Agronomic Performance
When companies or academic labs develop transgenic plants with traits to be proved envir-
onmentally safe, they still need to pass a performance test where growth and yield are
assessed under practical field conditions. Again we use transgenic maize as an exemplary
case study together with a variety of conventional comparators. Variety registration is a sub-
stantial requirement for any new crop brand and varieties in many countries. The evaluation
process is governed by independent bodies like the Federal Variety Registration Office in
Hanover, Germany. Companies need to send seeds of the new varieties that can be
grown on several contracted farms in representative locations in Germany. The comparative
approach of yield and performance ensures that farmers get the best available varieties and
information. Any new GM corn varieties must be tested in the same way as are non-GM
conventional varieties. They will be registered only if their agricultural performance is
improved in comparison to standard varieties. Here we present a representative dataset of
field performance of several candidates for variety registration in Germany (Fig. 13.5).
In these studies many plant attributes were tested. Resistance against European corn
borer and kernel yield serve as examples, but many traits are considered. The data show
that superior yield of GM corn is not always evident in comparison to conventional var-
ieties. Transgenic events need to be integrated into elite variety lines by classical breeding
(see Chapter 3). As we have seen, the genetic background is very important and may also
lead to very different performance levels depending on the environmental and climatic con-
ditions at a given site. However, corn borer infestation was dramatically reduced in Bt var-
ieties, leading to various slight yield increases compared to those of three conventional
maize varieties. An additional benefit might also stem from the fact that high-cornborer
infestations can increase the chance of infections with plant pathogens, such as fungi
that produce mycotoxins. Thus, decreasing incidence of pathogens and other indirect
13.5. PROOF OF BENEFITS: AGRONOMIC PERFORMANCE 319