Genetics - Theses
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ItemThe genetics of resistance to lufenuron in Drosophila melanogaster( 2005-02)The rise of large scale agriculture in the 20th century created the need for effective strategies to control insect pests. Treatment with chemical insecticides has been a weapon of choice, but the inevitable evolution of resistance has followed in many insect species. Resistance represents a major challenge, not only for agricultural production, but also for environmental preservation and human health. Two major options for resistance have been identified, and these are target-site based and metabolic-based resistance. Much insecticide resistance research focuses on identifying these mechanisms through genetic and molecular analysis. The insecticide lufenuron is the focus of this study. It belongs to a novel insecticidal group called the insect growth regulators, which were introduced in 1970s as highly selective insecticides with low vertebrate toxicity. Resistance to lufenuron in the non-pest species Drosophila melanogaster has been observed in field populations, despite the lack of field usage of lufenuron (Wilson & Cain, 1997; O’Keefe, 1997). This study has taken advantage of this phenomenon to investigate resistance mechanisms in natural populations. At least two detoxification mechanisms were identified. (For complete abstract open document)
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ItemThe role of cytochrome P450s in pyrethroid resistance in the AN02 strain of Helicoverpa armigera( 2003)Helicoverpa armigera is a lepidopteran moth species that is one of the largest agricultural pests in the world. In Australia, it is especially damaging to the cotton industry. Previous research on pyrethroid resistance in Helicoverpa armigera has suggested several resistance mechanisms present in the field. Research on a specific strain of H. armigera, AN02, suggested that resistance to pyrethroids in this particular strain is due to metabolism of the insecticide by cytochrome P450. This thesis describes work undertaken to gain further knowledge of the resistance mechanism present in this strain. Chapter 2 describes expression testing and elimination of the CYP6B cluster of P450s as candidates for resistance in the AN02, which were the most likely candidates available at the time. Chapter 3 describes construction, probing and sequence analysis of a midgut cDNA library of H.armigera to clone more P450 sequences and analyse the general transcriptome of one of the tissues where detoxification is likely to occur. Chapter 4 describes expression testing of new P450 sequences obtained from different sources to determine whether any of them have increased expression that is associated with the resistance genotype. Several new P450 genes were found to have increased expression and are candidates for further study.