**4. Disclaimer**

334 Pesticides in the Modern World - Risks and Benefits

female biased sex ratio is important for biocontrol agents, especially parasitoids because

It is clear from the foregoing that Bt maize may impact on parasitoid fitness as well as sex

It is difficult to determine, from existing literature, whether the observed host mediated effects of Bt maize on parasitoids are direct or indirect. Parasitoid performance can be affected as a result of the Bt toxin reducing host's biomass (Farrar and Ridgeway, 1995; Deml et al., 1998), or changing the host hemolymph-pH, hemolymph ion concentration, and nutrient concentration (Tanada and Kaya, 1993), which in turn can affect the parasitoid larvae living in the hemolymph. Alternatively, parasitoid larvae may be affected by ingesting the Bt toxin present in the hemolymph. Whatever the case, the most important consideration should be whether Bt maize can cause significant harm to stem borer natural enemies and most significantly the overall environmental consequences of such impacts. In order to determine the overall impact of growing Bt maize on stem borer natural enemies, the issues raised in this chapter should be placed in the context of real-life scenarios, taking into account *inter alia*, local agricultural practices, agro-ecological conditions, trade policies

This review has confined itself to potential impacts of Bt maize on stem borer natural enemies, specifically parasitoids and it is therefore not possible to make generalizations. Any judgment on the potential impact (s) of Bt maize, or any transgenic crop for that matter, should be made on a case-by-case basis using a rational, evidence-based scientific approach. In contrast to application of chemical insecticides with contact toxicity, insecticidal proteins expressed by GM plants have to be ingested to affect parasitoids. Consequently, when assessing the potential impacts of growing Bt maize on natural enemies it may be necessary to assess which organism (s) may be exposed under actual field conditions, and at what level. Indeed, the level at which an organism can be exposed to a plant expressed insecticidal protein may vary depending on the concentration of the toxin in the plant or environment, the plant tissue in which the protein is expressed, and the feeding behaviour of the non-target organism (Dutton et al., 2005b; Romeis et al, 2008a,b,c). Therefore exposure pathways can be predicted only if the relevant information for the GM plant, the environment and the natural enemy is available. Also, it may be necessary to make comparisons between the potential consequences of Bt maize on natural enemies and the use of conventional insecticides. Evidently, most studies have focussed mainly on making comparisons between Bt maize and non-Bt maize, without looking at the alternatives. It is only when a comparative approach is adopted that it may be possible to make prudent judgements regarding this novel method of insecticide delivery. Therefore in assessing the potential impact of Bt maize on the environment, it would be useful to pose the question: how would the use of Bt maize compare to the alternative (s)?" When assessment is not comparative decision making becomes non-objective. For example, it may be known that Bt maize reduces wing lengths of some stem borer parasitoids. However, with this information alone it may not be possible to reach useful conclusions. In contrast, if comparisons were made between the effects of Bt maize and the alternative (s) e.g., broad spectrum insecticides (effect on natural enemies), it would be easier to make more informed and objective

only females contribute to pest mortality upon release (Waage, 1982).

ratios and hence could possibly affect parasitoid biocontrol potential.

conclusions (and hence decisions) regarding this novel technology.

**3. Conclusion** 

etc.

The views expressed in this article are those of the individual authors and do not necessarily reflect the views and policies of the International Centre for Genetic Engineering and Biotechnology or the University of Venda.
