Abstract/Summary

The use of genetically engineered (GE) crops promises to deliver remarkable results from an environmental, economic and human health point of view. Presently, the world area planted with GE crops is devoted mainly to three sorts of genetic alteration, herbicide tolerance, insect resistance (IR) or a combination of both. In this thesis, the discussion focuses on genetically engineered insect resistant (GEIR) crops expressing toxins from the soil bacteria Bacillus thuringiensis (Bt) producing Crystalline (Cry). The prevailing scientific opinion is that although GEIR crops carry a certain degree of uncertainty, the potential risks are not considerably different to those associated with insecticides. Given the current understanding, the actual dispute about the risks is based mainly on the potential long-term effects, including gene slipover, development of pest resistance and the impact on non-target organisms. A further concern is that insect species that are not susceptible to the expressed toxin will develop into secondary pests and cause significant damage to the crop. In this thesis, the causes and impact of secondary pest outbreak are reviewed, analysed and incorporated within a novel bio-economic modelling framework. The bio-economic model takes into consideration the dynamics of two pest insects competing for the same resource and the resultant impact on maize farmers’ net returns. The modelling developed culminates with the inclusion of spatial features explicitly represented. The resulting bio-economic spatially explicit population model evaluates the development and impact of an invasive species that is not susceptible to the insecticide toxin expressed by the transgenic crop. This work provides insights and future recommendations for academic research, policy makers and farmers regarding the control and management of a new incursion of hazard (non-native) species. The research undertaken in this thesis aims to fill an important research gap on the impact of secondary pests GEIR crops, in particularly Bt maize. Overall, the results show that the use of Bt maize could indeed bring economic benefits to farmers while decreasing the burden of insecticides. It is also demonstrated that farmers need to be conscious of the possibility of an outbreak of a secondary pest and the consequences of this on yields and farm profits. Depending on several factors, it may take a number of years for secondary pests to proliferate to relevant levels of importance, thus the need to understand pest dynamics.