Interactions between the green peach aphid, Myzus persicae (Hemiptera: Aphididae), the entomopathogenic fungus Lecanicillium muscarium (Ascomycota: Cordycipitaceae), and a common parasitoid Aphidius colemani (Hymenoptera: Braconidae), were tested with Brussels sprout (Brassica oleracea var. gemmifera L. cv. Bedford Winter Harvest) as host plant, under laboratory and controlled field conditions. The effects of temperature, relative humidity and developmental stages of M. persicae on the efficacy of this fungus were measured under laboratory conditions. The most effective method of co-applying these two biological control agents to enhance their additive interactions against M. persicae was also assayed, in particular to determine if fungal infection of the aphid host had an effect on the number of aphids mummified by the parasitoid, and on emergence rate and parasitoid sex ratio. Although this fungus can be grown at a broad range of temperatures (15–30°C), the optimum temperature for control of M. persicae ranged between 20°C and 30°C. Lecanicillium muscarium had high efficacy as a microbial control agent against M. persicae between 55% and 90% RH. Furthermore, the fungus was most virulent against adults and older developmental stages, compared to young developmental stages of M. persicae. Results also showed that although fungal infection has no negative effect on the rate of nymph production per day, total fecundity of infected aphids declined overall as the length of the reproductive period of the aphids was reduced. In no-choice and choice experiments under laboratory conditions, mummification, adult emergence from mummified aphids and female sex ratio in emerging adults, were unaffected when the fungus was applied 6 or 7 days after the parasitoid was added, compared with treatment by A. colemani alone. However, all parameters were significantly lower when L. muscarium was applied first, compared with treatment by A. colemani alone. Co-application of A. colemani or exposure to naturally occurring parasitoids and L. muscarium can interact positively, leading to increase the control level to be higher than equivalent level produced by one agent alone but less than additive effects in a field cage experiments. Laboratory experiments showed that aphids feeding on rye were the most susceptible to infection by L. muscarium. The highest percentage of aphids mummified and emergent parasitoid females were found in aphids feeding on green pepper. Further research is required in large scale open field conditions to study the combined effects of the fungus and either naturally occurring or introduced parasitoids on aphid population growth. The implications of these results for the use of L. muscarium and A. colemani in combination as a biological control programme are discussed.

Prostephanus truncatus (Horn) (Coleoptera: Bostrichidae) is a destructive pest of stored maize and cassava that has recently been accidentally introduced into tropical Africa. Males produce an aggregation pheromone when on food, that attracts dispersing males and females. P. truncatus aggregation pheromone is being used to monitor the spread of P. truncatus (Larger Grain Borer) across Africa. The biological function of this pheromone is controversial. This thesis investigates the role of aggregation pheromone in mate choice in P. truncatus. The literature on Coleopteran aggregation pheromones was reviewed, with particular reference to the possible adaptive functions of aggregation pheromones. Variation in Prostephanus truncatus aggregation-pheromone signalling was detected. Conspecifics can detect these differences and are preferentially attracted to some males more than others. Both males and females 'agree' which males are most attractive (shown in a laboratory bioassay and in trapping experiments in the field). Females also discriminate between potential mates on contact by a stylised pushing behaviour. Some males consistently secure more matings than others when two males are presented at once to a female. Discrimination between males mediated on contact through pushing is not influenced by the male's aggregation pheromone signal (both natural variation and manipulation of the pheromone signal were studied). Observation of adult beetles in an artificial host sandwiched between two glass plates revealed that males and females pair up, and cohabit within the same tunnel system. Pairs mate multiply (up to 20 times per 12 hours) and dissection of recently mated females revealed that males deliver an oversized ejaculate (approx. 50 000 sperm) as an oval spermatophore. Male investment in ejaculate was not found to be influenced by male crowding or the presence of Female Factor (an involatile pheromone produced by females, which can trigger aggregation pheromone shut down in males).

1. This thesis examines the anatomy, ultrastructure and mechanical properties of the metathoracic femoral chordotonal organ (mtFCO) in the locusts Schistocerca gregaria and Locusta migratoria. Some measurements were also made on the mtFCO of the giant grass hopper Tropidacris collaris. The mtFCO is of interest because of its complex mechanical linkages (the apodeme complex, Shelton et al. 1922) and its wide range of receptor response types (Zill, 1985; Field and Pfluger, 1989; Matheson, 1990). 2. Electron microscopy has been used in conjunction with modern image analysis techniques to provide the first comprehensive description of the composition of each of the mtFCO's mechanical linkages. 3. This thesis provides the best evidence so far that the mtFCO of the locust is formed from two fused scoloparia, each of which is innervated by a separate branch of the CO nerve (nerve 5b1). It has been shown for the first time that the neurones of the mtFCO can be subdivided consistently into 6 discrete populations, each of which is innervated by a separate bundle of axons. Neurone size, shape and orientation vary between the populations. 4. The dendrites of the sensory neurones terminate the pairs in specialised scolopale cells in a manner similar to that previously described in other insect COs. This thesis provides the first description of the dendritic distortions which occur upon stimulation of an unfixed sense organ. 5. Biomechanical investigations have revealed that the mtFCO is a viscoelastic system. The results from this thesis suggest that the organ's mechanical properties are likely to be partly or wholly responsible for two documented phenomena common to all COs; hysteresis of the sensory output in response to cyclic elongation/relaxation (Burns, 1974; Matheson, 1990, 1992) and adaptation in firing rate following a step displacement (Usherwood et al., 1968; Theophilidis, 1986).

Extrapolating biodiversity patterns across spatial scales can address shortfalls in our knowledge of species distributions, inform conservation and further our understanding of spatial patterns in biodiversity. I compared fine grain predictions of occupancy for British Odonata species among ten downscaling models. I observed a sigmoidal occupancy-area relationship for the best performing model and found that predictive success for Odonata species varied systematically with species traits. Species with high dispersal abilities had greater predictive error. Poorer predictions for species with a climatic range limit in Britain suggest that environmental information is required to fully capture spatial patterns in biodiversity. I modelled the distribution of the Brindled Green moth at two spatial grains using a hierarchical Bayesian model to quantify associations with climate, landcover and elevation, whilst accounting for residual spatial autocorrelation and spatial patterns in recording effort. Model predictions improved at the finer spatial grain and identified unsurveyed grid cells with high suitability for future recording. The overlap between individual species distributions underpins spatial patterns in multi-species assemblages. I used simulated species assemblages to evaluate 29 abundance-based metrics of β-diversity against a set of desirable and ‘personality’ properties. Metrics accounting for unseen shared and unshared species were lacking. I identified a trade-off between robustness in the face of undersampling and sensitivity to turnover in rare species. The findings were borne out when a selection of metrics were applied to assemblages of British macro-moths: variation in β-diversity was best explained by climate, landcover and distance when using standardised data and abundance-based metrics, as opposed to opportunistic data and presence-absence metrics. This thesis has demonstrated the value of using biological records to explore biodiversity patterns at multiple spatial scales and has highlighted some of the methodological challenges that remain.

No description available.

The thesis is mainly concerned with the structure of the protein in the egg case of the praying mantis. It continues the work of Rudall (1956), who showed that the protein was organised into lamellae and had an α-helical structure. He put forward two models: hexagonally packed α-helices, and two-stranded coiled coils arranged in layers. In the latter model, each coil is staggered from its neighbours by a quarter of the pitch, so as to allow optimum packing. Sections on the X-ray diffraction camera, analysis of errors in reciprocal lattice coordinates, analysis of sequences of fibrous proteins, and unsuccessful structural studies on sequential polyheptapeptides are also included. Lamellae may be removed from fresh egg cases, and ribbons from egg cases a few or more hours after production. Electron microscopy of negatively stained lamellae, positively stained lamellae and sectioned ribbons, and X-ray diffraction studies on the ribbons make it possible to postulate a model for the structure. The model is more detailed than Rudall's and has differences. It has layers of two-stranded α-helical coiled coils about 18Å thick packed in register to form 460Å thick lamellae about 1μm x 10μm. The layers are perpendicular to those in Rudall's model. The lamellae pack into ribbons with considerable disorientation. Coiled coils within an 18Å thick layer probably pack in a way similar to that in the layers of Rudall's model with a stagger of 2.5 x the pitch and a rotation of 90° between adjacent coiled coils. Each coiled coil has chains about 730 Å long staggered by about 55Å. Coiled coils interact end to end with an overlap of about 40Å, so as to leave gaps of about 15Å. The molecular length of 730Å is consistent with the molecular weight of 53,000 estimated from SDS gel electrophoresis. The molecular axis is parallel to the principal shear plane in the lamella. Fibres of this protein drawn from the first order gland give an X-ray diffraction pattern indicating a very similar structure. In the presence of water, uranyl acetate solution, neutralised phosphotungstic acid or a mixture of chlorobenzene and bromobenzene, the volume of the unit cell changes. X-ray diffraction evidence indicates that sliding occurs between coiled coils as the volume changes. The amount of lateral swelling is greater in the direction perpendicular to the surface of the lamella than in the direction parallel to it. Together with the different extents of the lattice in these directions, this is consistent with the model, which is different in these two directions. A discussion is included on the literature relating to X-ray diffraction cameras using a Frank s mirror and a quartz crystal monochromator. To this has been added calculations concerning focal size, resolution and intensity of the X-ray beam. The results of these are embodied in a discussion of camera design. An appendix is devoted to a method of estimating standard errors of reciprocal lattice coordinates. The analysis of the sequences of fibrous proteins and the statistical basis of this analysis are discussed in appendices. Preliminary calculations on tropomyosin have revealed periodicities which can be related to a 14 residue stagger between chains, in agreement with Hodges et al (1973), and to the repeat of the actin helix. Hydrophobia residues and possibly positively charged residues are arranged in a pattern which, on the present limited data, appears to be important in interactions with actin. Residues generally considered to disrupt helical structures are arranged in a band coiling around the α-helix. A technique enabling the D stagger in collagen to be identified is described. This also gives information which suggests how hydrophobic interactions are important in defining the pitch of the collagen molecules and the interactions between them. Arguments based on this technique show how pairs of opposite charges lead to interactions consistent with a five-stranded microfibril. There is also an appendix on attempts to produce oriented arrays of sequential polyheptapeptides, in order to obtain X-ray diffraction patterns. Another appendix describes how the colony of praying mantids was raised.

Cytochrome P450s, including CYP6M2 gene, are involved in the detoxification of permethrin. Some of these genes are regulated by CnCC / dKeap 1 and Spineless / Tango in Drosophila melanogaster. This mechanism is yet to be identified in Anopheles gambiae. Thus, we examine whether there is differential regulation of CYP6M2 gene between permethrin resistant Tiassalé and susceptible Kisumu strains of An. gambiae. Bioinformatics analysis was used to search for cis-acting elements within CYP6M2 (896 bp) region hypothesised to contain the promoter. Isolated and cloned CYP6M2 promoter reporter constructs were transfected into Anopheles gambiae Sua 5.1* cells to measure luciferase activity as a surrogate promoter activity. The WHO adult bioassay was used to expose adult females of the permethrin resistant Tiassalé and susceptible Kisumu strains of An. gambiae to discriminating doses of 0.75% permethrin. Uncharacterised strains from Auyo (Auyo-Nigeria) selected to 4% DDT and 0.1% Bendiocarb as recommended by WHO were also studied. Total RNA was isolated from the respective selected and unselected strains of An. gambiae and cDNA synthesised. Semi and Real time quantitative PCR (qPCR) using SYBR® Green were used to determine the gene expression and regulation levels. Results established the presence of putative AGAP010259 (AhR) and AGAP005300 (Nf2e1) cis-acting elements within Anopheles gambiae CYP6M2 promoters in silico. Luciferase reporter gene assays revealed no promoter activity as confirmed by using CYP9M10 promoter from Culex quinquefasciatus with a known promoter activity as control. There is higher expression of Nf2e1 than AGAP010259 and a variable expression of CYP6M2 in all the insecticide selected individuals, which may potentially be associated with insecticide resistance. This study provides useful information on our understanding of the regulatory mechanisms involved in insecticide resistance. These results have implications for the control of mosquito populations and the global spread of human, livestock and poultry diseases.

Cross-tolerance to environmental stresses results from the synergistic co-activation of defence pathways that cross biotic-abiotic stress boundaries. However, the signalling mechanisms that underpin such responses remain poorly characterised. The effects of an abiotic stress (high light; HL) on the responses of Arabidopsis thaliana and tobacco (Nicotiana tabacum) plants to a biotic stress (infestation by the green peach aphid, Myzus persicae) were therefore analysed. Particular focus was placed on the role of cellular redox state as a regulator of cross-tolerance phenomena and the identification of signalling pathways that underpin aphid resistance. Aphid fecundity was measured in a range of A. thaliana mutants that have defects in non-enzymatic antioxidants (ascorbate and glutathione), enzymatic antioxidants (catalase) or downstream kinase/phosphatase signalling cascades, and in transgenic tobacco lines that have either increased or decreased levels of ascorbate oxidase. A pre-treatment with HL increased the resistance of transgenic tobacco plants with low ascorbate oxidase to aphid infestation. In contrast, the A. thaliana ascorbate oxidase knockout mutants did not show the HL-dependent decrease in aphid infestation. Aphid fecundity was decreased on A. thaliana mutants that have altered antioxidant (ascorbate, glutathione, catalase) status, or that lack the gamma (γ) subunit of protein phosphatase (PP2A). A pre-treatment with HL increased the resistance of A. thaliana plants to aphid infestation in all of the genotypes, except for the cat2 mutants that lack the photorespiratory form of leaf catalase and glutathione defective mutants. Taken together these findings demonstrate that redox processes and oxidative signalling are important modulators of aphid resistance and the light-aphid interaction. Moreover, the analysis of aphid fecundity on these A. thaliana mutants, which also have different levels of leaf camalexin, suggests that the levels of this secondary metabolite alone do not influence aphid infestation. A transcriptome and metabolome profiling analysis of the responses of the different tobacco lines highlights the central role of cell wall modifications/signalling as key components in plant responses to aphid infestation.

No description available.

No description available.