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.

No description available.

This project sought to deliver new understanding of the responses of pest insects to light for the purpose of improved agricultural pest control. Through access to experimental polyethylene horticultural films with novel transmission properties, I exploited new opportunities for exploring separate short- and long-wavelength mechanisms for pest suppression. The early experimental work of the project tested the effect of short- and long-wavelength ultraviolet light on the population growth of the generalist aphid, Myzus persicae, on cabbage (Brassica oleracea) plants. These polytunnel field experiments established new hypotheses for the role of long-wavelength ultraviolet radiation as an environmental cue for damaging short-wavelength ultraviolet radiation. Through a series of methodological developments, I quantified both the dose-response of environmentally-relevant ultraviolet on M. persicae mortality, and proposed a colour behavioural model for the feeding behaviour of M. persicae under different illumination conditions. Through synthesising these findings into a model of aphid hazard-avoidance, I show that the behaviour of M. persicae may be manipulated to increase its exposure to solar short-wavelength radiation, with consequences for population growth rate. As such, this mechanism may be used in protected agricultural practice as part of a wider integrated pest management strategy.

Phytoplasmas are insect-transmitted plant pathogenic bacteria that dramatically alter plant development. Phytoplasma virulence protein (effector) SAP54 mediates degradation of host MADS-box transcription factors (MTFs) via 26S proteasome shuttle protein RAD23 to abolish normal flower development and produce leaf-like flowers (phyllody). Phyllodies are common symptoms in phytoplasma-infected plants worldwide. Why do phytoplasmas degrade MTFs and induce phyllody? Are changes in host plant morphology adaptive and benefit phytoplasma spread? Because phytoplasmas rely on their insect (leafhopper) vectors for transmission from plant to plant, I hypothesized that the vegetative tissues of the leaf-like flowers render plants more attractive to the insect vectors that will aid phytoplasma dispersal in nature. I discovered that the induction of phyllody is genetically linked with enhanced insect egg-laying preference on the infected plants that exhibit the leaflike flower phenotype. However, SAP54 enhances insect colonisation of plants independently from floral transition and the changes in plant morphology. Interestingly, male leafhoppers are required for the preference of females to lay eggs on SAP54 plants. Moreover, SAP54 suppresses insect induced plant responses in sex-specific manner by selectively downregulating male-induced defence and secondary metabolism pathways. Furthermore, I identified four MTFs that are expressed in plant leaves and play important roles in egg-laying preferences by leafhoppers and demonstrate sex-specific regulation by SAP54. Taken together, phytoplasma effector SAP54 enhances insect vector colonisation of plants by suppression of insect-induced plant responses independent of developmental changes. This is likely to occur by targeting MTFs – a conserved regulators of both plant development as well as plant defence against herbivorous insects. In addition to developmental changes, degradation of MTFs by SAP54 may result in modulation of male-induced plant responses to attract female insects for egg-laying and aid phytoplasma spread in nature.

The interaction between an increasing global human population and a number of important long-term trends and issues are putting strain on food production. Insects represent a significant food security concern causing up to 15% of global crop losses. Conventional chemical methods are ineffective; inducing resistance and degrading the environment. Sustainable alternatives are sought. The sterile insect technique provides a sustainable solution. Genetic engineering can augment this historic technique by replacing radiation-induced sterilization with sperm-specific nuclease expression to introduce double-stranded DNA breaks in the gametes of mass-reared and released males. This paternal-effect system is dependent on elucidation of appropriate sperm-specific promoters and suitable chaperone-nuclease combinations. This thesis develops this technology in the SIT neglected insect orders, the Lepidoptera and Coleoptera. Specifically the Plutella xylostella (Plutella xylostella, L.) and the red flour beetle (Tribolium castaneum, Herbst). I provide the foundations for a paternal-effect genetic-control-system in both species by developing a conditional sperm-specific expression system in Plutella xylostella and a female-specific expression system in Tribolium. Mass-rearing insects for the genetic control of a species can be augmented by recent developments in RNAi. I show that the sex ratio of Tribolium can be adjusted by treatment with dsRNA transformer, producing pseudomales as an additional bonus. In addition, an exploratory data analysis of producing transgenic lines in insects using piggyBac was undertaken. As well as providing a comprehensive compendium and assessment of the transgenic literature, something not yet published elsewhere, a predictive model was produced that could be very useful to a wide diversity of researchers in insect molecular biology, developmental biology, disease biology and genetics. It is hoped that this work will contribute towards the effective control of the Plutella xylostella in the near term, and form a model for the sustainable control of other lepidopteran and coleopteran species through genetic pest management.

No description available.

The well-established herbicide, asulam (methy14-aminobenzenesulphonylcarbamate; M&B 9057) is used widely for control of weed species including docks and bracken. The compound resembles sulphonamides in structure. Most of an oral dose of asulam is eliminated from rats mainly in the urine (75%) and faeces (19%) within 24 hours. Biotransformation in the intact animal is similar to the N-acetylation of some sulphonamides. The major metabolite is N4-acetylasulam which is excreted rapidly in the urine (15% male; 9% female) and also appears in faeces (4%). Induction of rats with asulam does not effect overall metabolism and excretion except that decarbamoylation is increased in the gut. N4-acetylsulphanilamide is also produced ( 2%) by decarbamoylation in the gut. N4-acetylasulam formation in vitro is located in the cell-membrane fraction of liver. Asulam is not eliminated in the bile (1% dose) in vivo. No binding spectrum is obtained with microsomal cytochrome P450. Continuous perfusion through liver for 6 hours does not increase biliary elimination, but at least three water-soluble unidentified compounds (4.5%) are formed in plasma. In contrast to the in vivo state asulam causes rapid oxygen uptake in vitro with microsomes producing an isolatable colored metabolite (max = 330 nm) which contains ring-substituted hydroxy sulphonamido and nitrogen substituted carbamate groups. Mass spectrometry shows this not to be 2-hydroxyasulam.

The rice blast disease caused by the fungus Magnaporthe oryzae causes significant annual crop losses of up to 30%. The fungal specific cell wall is a potential antifungal target due to the external location and importance to fungal survival and morphogenesis. The skeletal framework of the cell wall is made from glucan chains cross-linked with chitin, facilitated by the Congo Red Hypersensitivity (Crh) enzyme. In Saccharomyces cerevisiae, ΔCrh1/ΔUtr2 mutants exhibit reduced wall integrity and the same is observed in Candida albicans, with reduced virulence in a mammalian host. Little is known about the cell wall in fungal plant pathogens and nothing of the Crh orthologs. Bioinformatics revealed five M. oryzae Crh-like genes lying in two clades. Gene expression analyses revealed up to four-fold elevated expression of MGG_Crh2 and MGG_Utr2 when grown under cell wall stress. Consistently, the corresponding deletant strains showed hypersensitivity towards cell wall perturbants and was attributed to a loss in cell wall rigidity. Cell wall analysis of the mutant ΔΔMGG_Crh2_Utr2 revealed changes in the cell wall composition consistent with the reduction of Crhp activity and activation of cell wall compensatory mechanism often observed in a compromised cell wall. Furthermore, eGFP-tagged MGG_Crh2p showed localisation to the lateral cell wall with high accumulation at septum and polarised growth sites, consistent with sites of chitin accumulation. These mutants are, however, able to form normal infective structures and are fully pathogenic on susceptible rice cultivars. In conclusion, the Crh gene family in M. oryzae is important for cell wall integrity by the cross-linking of chitin to glucan, but dispensable for virulence. Future work should explore the compensatory mechanism of other cell wall proteins in the ΔΔMGG_Crh2_Utr2 as this could shed light on the potential for targeting multiple cell wall components in a synergistic approach to confer effective disease control.

Insect pests of agricultural significance pose substantial risks for food security in an ever-growing global population. Conventional control measures used against these pests have had varying degrees of success and examples of pesticide resistance and offtarget effects of pesticides highlight the urgent need for the development of new, environmentally benign control methods. Deployment of ‘self-limiting’ insects is a species-specific approach that can be used to combat many species, including two major agricultural insect pests, the Medfly, Ceratitis capitata, and the Diamondback moth (DBM), Plutella xylostella. In this thesis, I used transgenic ‘self-limiting’ strains of medfly and DBM to stress-test self-limiting technology in laboratory and field scenarios. In Chapter 2, I tested the effect of larval diet composition on the penetrance of a female-specific self-limiting system in the OX3864A strain of medfly under simulated control conditions. In Chapter 3 I investigated the potential for resistance to selflimiting systems, using artificial selection for survival under a low dose of the transgene antidote, in the OX3864A medfly strain. In Chapter 4 I used the OX4319L self-limiting strain of DBM and showed that its responses to an artificial pheromone source in wind tunnel flight trials were comparable to the wild type. I also described the field dispersal characteristics of a long-term, laboratory-reared wildtype DBM strain in a mark-release-recapture trial. In Chapter 5 I demonstrated that the OX4319L DBM strain had comparable field longevity, but reduced mating competitiveness, in comparison to a wild-caught DBM strain. Finally, in Chapter 6, I discuss the broader context and address the practicalities, regulatory controls and implications of transgenic technologies for insect pest control under open field conditions.

No description available.