Cotton pests and natural enemy interaction in Uganda: A basis for biosafety risk assessment.
Cotton in Uganda is attacked by many insect pests causing yield losses of between 30 – 80%. The biggest losses are caused by members of Lepidoptera. Use of chemical insecticides have been by been used as an approach to address the pest problem in cotton. Nevertheless, because of the cryptic nature of Lepidopteran pest on cotton, chemical pesticides have not been very effective in controlling the pests. Furthermore, pesticides are expensive and are associated with a number of problems. Consequently there has been a need to access new technologies for managing the pest of cotton and one such technology is genetic engineering. With the current advances in the use of genetic engineering in management of cotton pests, there is increasing pressure to adopt these technologies. However, before this technology can be introduced it is important to assess the bio safety risks associated with the technology. It is important to understand the danger and potential long term impacts the technology will have on the environment and associated ecosystem services. Article 16.2 of the Cartegena Protocol calls for assessments of the risk to the environment before introduction of genetically modified organisms are introduced. Understanding a good risk assessment requires significant amount of information on plant-natural-enemy interactions, a process that creates and maintains ecological processes. There is paucity of information on arthropod species and ecological processes in cotton growing systems which make it difficult to assess the risks that may be associated with the introduction of genetically modified cotton. And because there are very many species in and near the cotton cropping system, it is impossible to evaluate the risk to every species. It is therefore important to identify the different and most relevant species or ecological processs in the target region of release of the geneticall modified cotton. It’s against this background that the work reported in this thesis was under taken to: document species and ecological processes of arthropods that occur in the cotton cropping system; establish and prioritize the potential likely exposure and adverse effect pathways of the transgene to non-target cotton arthropods; understand the dynamics of some selected cotton pests and their natural enemies in cotton as influenced by Bt-biopesticide and understand the influence of inherent plant factors on the searching behaviour and sensory ability of the ladybird beetles. The study results identified that the arthropod community in cotton which is comprised of 67.0% beneficial arthropods and 33.0% herbivores (target and non-target) is categorized in three priority groups with 41% of the arthropods in the highest, 32% in the intermediate and 27% in the lowest priority category of being affected if GM cotton was to be introduced. The study further developed adverse-effect scenarios for the priority arthropod and process through bi- and multi-trophic exposure pathways. In the species assessment, an adverse-effect scenario was mainly through hypothetical changes in a population parameter, population density or with a behaviour resulting from the possible exposure. These changes alluded to a possible change in ecological functions or functions of the population which were then evaluated as adverse or beneficial. These potential adverse effects pathways and damage potential helped in the formulation of different generic hypotheses. xiii The proxy for GM-Cotton, XenTari (Bt-biopesticide) had very minimal control over aphids, but impacted the survival of the ladybird beetles. The results therefore revealed that, if XenTari which targets lepidopteran pest was introduced, the aphids will constantly be exposed. This exposure may cause increased fitness of the aphid and subsequently increasing their outbreak potential. Secondly, the limited control of aphids by XenTari may further lead to an increase in the aphid populations and subsequent continued use of chemicals. Ladybird behavioral studies highlighted that, the main events and sequence of behaviors exhibited were; searching, encountering and feeding on the prey. Whereas searching was the most frequent behavioral event for both the adults and larvae, more time was registered on feeding by the larvae. These findings lay a foundation to bridging some of the information gaps in preserving the plant-pest –natural enemy interactions and biodiversity in general as insect-resistant genetically modified cropping systems become a cornerstone tool of modern integrated pest management and provide a framework for bio safety risk assessment for cotton and other crops in Uganda.