The mechanisms of resistance to the Bacillus thuringiensis crystal toxin Cry1Ac were explored in the Plutella xylostella SERD4 population, which shows polygenic resistance to Cry1Ac with cross-resistance to the pyrethroid deltamethrin that can be partially overcome by co-administering the esterase inhibitor piperonyl butoxide (PBO). The novelty of SERD4 cross-resistance was confirmed by testing other Cry1Ac-resistant populations for resistance to deltamethrin and for synergism of Cry1Ac toxicity by PBO. Esterase-mediated sequestration of Cry1Ac was tested using electrophoretic mobility shift assays, gut esterase activity inhibition assays and ligand blotting. Additionally, isozyme profiles and gut esterase activity were compared between various populations in an attempt to correlate the pattern and activity of esterases with cross-resistance. No correlation was found between esterase isozymes and Cry1Ac resistance and no evidence was found to indicate a direct interaction between CrylAc and esterases. Previous work showed that a maternal effect contributes to Cry1Ac resistance in SERD4. Therefore factors that are known to be maternally inherited in Lepidoptera and which have been implicated in Cry1Ac resistance were screened to investigate possible correlations with resistance. Various immune parameters were screened including both cell-free and haemocyte-mediated responses. No correlation was observed between immune status and Cry1Ac resistance. The composition of the gut microbiota was compared between SERD4 and a susceptible P. xylostella population and eliminated to assess any contribution to Cry1Ac toxicity. The microbiotas of resistant and susceptible larvae were identical. Furthermore, the gut microbiota of a Cry1Ac-susceptible strain that is adapted to artificial diet was not observed to affect Cry1Ac toxicity. This led to further work concerning a recent novel hypothesis that gut bacteria are obligately required for the toxicity of B. thuringiensis and Cry1Ac towards numerous lepidopterans including the tobacco hornworm, Manduca sexta. Techniques were developed to allow the rearing of aseptic M. sexta larvae. The toxicity of B. thuringiensis was not reduced in the absence of gut bacteria. However, B. thuringiensis was less toxic to larvae that had been recently exposed to antibiotics. Antibiotic exposure did not reduce the toxicity of Cry1Ac.

Variation in parasitoid responses to semiochemicals may be influenced by genetics, phenotypic plasticity and the individual's physiological state. Previous experimental work has indicated a high degree of variability among parasitoid individuals in their response to aphid sex pheromones but no work has been done to investigate the factors behind such variation. Some aspects of this variation were investigated in the aphid parasitoid Aphidius ervi (Haliday) (Hymenoptera: Braconidae) in the laboratory. Conducting behavioural experiments, the searching behaviour of females was investigated in the presence and the absence of the aphid sex pheromone (4GS,7S,7a/?)-nepetalactone, observing the same individual female parasitoids during two consecutive foraging attempts on different plants. The first set of observational experiments demonstrated the role of the pheromone as an arrestant in the searching behaviour of A. ervi and its additive effect when it was presented with other foraging cues such as aphid-induced plant volatiles. The second set of behavioural experiments showed significant differences in A. ervi responses to the pheromone depending on their physiological state. Virgin, well-fed and high egg-load females were more active in the presence of the aphid sex pheromone than mated, hungry and low egg-load females although there were no significant differences in their activities in the first foraging attempt when the pheromone was absent. The effect of the pheromone on the searching behaviour of A. ervi within different tritrophic systems was investigated. The results showed variation in this response depending on which host aphid and/or the host plant they had been reared, showing that "conditioning" may have an influence on this response. Using two isofemale lines and an insectary-maintained laboratory population of A.ervi, the genetic basis of this response was investigated. The behavioural experiments showed no significant differences between the three different populations in their response to aphid sex pheromones. A supportive molecular study using DNA microsatellites v/as also conducted, which revealed low genetic variability among the three studied populations. The results are discussed in the context of using the response of A. ervi to aphid sex pheromones in a strategy to manipulate natural populations of the parasitoid for the biological control of aphids and the importance of studying the variation in this response to increase the effectiveness of such strategy.

No description available.

The research reported in this thesis investigated the ability of <italic> P. melanarius</italic> to control slug populations, and the impacts that alternative prey, particularly carrion, has on the efficacy of this predator as an agent of slug pest control. A suite of laboratory- and field-based experiments were conducted to achieve those ends. The main findings were: (1) Prey vital status was significant in determining the feeding preference hierarchy of <italic> P. melanarius.</italic> The mucus defence of live slugs (<italic>Deroceras reticulatum)</italic> deterred attacks by beetles, but feeding on dead <italic> D. reticulatum</italic> emphasized a preference for this prey type by <italic> P. melanarius.</italic> (2) The survival rate of <italic>D. reticulatum</italic> bitten by <italic>P. melanarius</italic> was not different to that of non-attacked control slugs. Attacking bites by <italic>P. melanarius,</italic> visited upon live slugs, did not yield slug DNA-positive results during molecular analysis of beetle foregut contents. (3) <italic>Pterostichus melanarius</italic> was not able to detect by olfaction the presence of live or 12 h-decayed dead <italic> D. reticulatum.</italic> (4) The feeding history of <italic>P. melanarius </italic> had a significant influence on subsequent prey selection. However, the effect interacted with an innate, overarching prey preference hierarchy. (5) A large-scale semi-field experiment identified that <italic>P. melanarius </italic> fed upon slugs, but the effect of predation pressure was not sufficient to induce negative growth in slug population density. The presence of alternative prey, and the increasing mass of individual slugs exerted rate-limiting effects on slug-predation by <italic>P. melanarius</italic>.

This thesis was aimed at the extraction, isolation and structure elucidation of insecticidally active secondary metabolites of Citrus aurantium plant parts for potential use either as commercial insecticides or as lead compounds. Fruits, leaves and shoots of C. aurantium were extracted in methanol and the chemicals recovered were fractionated by liquid-liquid partitioning using organic solvents of increasing polarity (petroleum ether, dichloromethane, ethyl acetate). Petri dish exposure bioassays revealed that only the petroleum ether fraction of the fruit methanol extract was toxic against Bactrocera oleae adults. The bioactive chemicals present in the fruits were produced and/or accumulated in the peels. Petri dish exposure and topical application bioassays revealed that a petroleum ether peel extract was toxic against B. oleae and Ceratitis capitata adults. In several cases, differences in susceptibility were revealed between the two species and between the two sexes of the same species. First gravity column fractionation of the peel extract revealed that only the F2 fraction was active, while fraction Ft has a synergistic effect. Further purification of the F2 fraction on the second gravity column, followed by HPLC, resulted in the isolation of three major compounds. The chemical structure of these components was elucidated by spectroscopic methods (UV, FTIR, GC-MS and *H NMR) and was assigned as osthol, bergapten and 6',7'- epoxybergamottin. Of the three isolated compounds, only the 6',7'-epoxybergamottin was active and its toxicity was the same to the synthesised 6',7'-epoxybergamottin. However, the synergism revealed between isolated bergapten and 6',7'- epoxybergamottin was not confirmed when isolated bergapten was replaced by synthetic bergapten, indicating that minor components present in the isolated bergapten were responsible for the synergistic effect. Crude or semi-purified peel extracts of C. aurantium may have potential for insect control. Moreover, 6',7'-epoxybergamottin has apparently never been reported to have deleterious effects on insects. At this early stage, the potential of 6',7'- epoxybergamottin as a lead compound for a new class of insecticides remains to be determined.

Bacterial biocontrol agents have previously been identified as alternatives to agrochemicals for the control of crop diseases. The advent of genetic engineering and the identification of the modes of biocontrol that bacteria possess has allowed the potential modification of successful inocula to improve their efficacy in biocontrol. A plant growth promoting rhizobacterium (PGPR) <italic> Pseudomonas fluorescens</italic> SBW25 (WT) was modified to contain the phenazine-l-carboxylic acid biosynthesis pathway. The genetically modified biological control agent (GM-BCA) 23.10 was previously shown to have improved biocontrol activity when compared to WT. The work described in this thesis assessed the natural microbial community structure and function in the rhizosphere of pea, wheat and sugar beet under field conditions and the potential impact of the release of a GM-BCA may have on these communities, using laboratory based mesocosms. In addition to this, an investigation in to the production and conservation of HCN biosynthesis was undertaken on global collection of biocontrol strains to assess the potential of HCN biosynthesis as another trait for genetic modifications. A detailed field study of the indigenous rhizosphere communities was undertaken using culturable microbiological techniques, carbon source utilization and the development of molecular community profiling approaches on bacteria and fungi. A dominating effect of the plant species was shown and specific enrichment was identified on soil communities with significant effect also seen relating to plant growth stage. These data provided a robust baseline data set for comparisons to mesocosm experiments assessing the potential ecological impact that the release of a GM-BCA may have on the environment. This mesocosm study demonstrated plant growth stage effect dominated shifts in community profile with transient perturbations of indigenous community structure and function identified as a result of the inoculation. The significant change with greatest persistence was the replacement of a large proportion of 7-proteobacteria communities by the inocula.

Plants may be genetically modified to express an entomopathogenic protein from the bacterium <italic>Bacillus thuringiensis</italic> (Berliner) (Bt plants). Bt plants are known to affect some above-ground invertebrates, with significant effects on species closely related to target invertebrates and on their natural enemies. Bt proteins may enter the soil through root exudates and decomposition of plant material. This study aimed to analyse the effects of Bt broccoli (<italic>Brassica oleracea</italic> L. var. italica Plenk) on six soil-dwelling invertebrates. No significant differences were detected in nematode (<italic>Panagrellus redivivus</italic> L.) populations living in compost in which Bt and non-5/ broccoli had grown. The other species were introduced to combinations of Bt and non-5/ leaves, and compost in which Bt and non-5/ plants had grown. No differences were detected in Collembola (<italic>Folsomia candida</italic> Willem) populations, but significantly more young woodlice (<italic>Porcellio scaber</italic> Latrielle) survived, and weighed more, in the Bt than the non-5/ treatments. Slugs (<italic>Deroceras reticulatum</italic> Muller) weighed more in the presence of Bt proteins. A higher percentage of earthworm (<italic>Lumbricus terrestris</italic> L.) cocoons hatched in Bt than non-5/ treatments. In contrast, at a third trophic level, fewer predatory beetles (<italic>Nebria brevicollis</italic> Fabricius) survived when feeding on slugs that had fed on Bt leaves than on those fed on non-5/ leaves. Leaves from Bt plants affected more parameters than compost in which Bt plants had grown. Attempts were made to use molecular techniques to analyse the effects of Bt broccoli on soil micro-organisms. Individual Bt broccoli plants expressed different concentrations of Bt protein. The Bt plant's control of three Lepidoptera species was tested and only one species was susceptible. These results show that non-target invertebrates, including pest species, can be affected by Bt broccoli, sometimes beneficially, and underlines the need for prior testing of GM crops on a range of non-target species.

No description available.

In spite of varying opinions as to the effectiveness of molluscicides in the control of schistosorniasis, the search for more effective and highly selective molluscicides should continue, so that adverse effects on non-target organisms caused by commercially available molluscicides may be reduced and the possibility of resistance guarded against. To this end, the differences in susceptibility to Frescon and 4'-chloronicotinanilide between the schistosome-bearing snail, Bulinus truncatus and a representative tropical food fish, Sarotherodon mossambicus, were examined and discussed in relation to the rate of uptake of these compounds and. their distribution among different organs. The rate at which water is taken up by B. truncatus and S. mossambicus has also been calculated and related to the rate of uptake of molluscicidos. This part of the work was an attempt to elucidate the mechanism of carriage of the chemicals into the animals being studied. It has been demonstrated that B. truncatus and S. mossambicus concentrate Frescon and 4'-chloronicotinanilide to high levels. For B. truncatus, both Frescon and 4'-chloronicotinanilide were concentrated in the psoudobranch, while in S. mossambicus the highest concentration of Frescon was found in the liver and that of 4'-chloronicotinanilide in the bile. The high tolerance of S. mossambicus to 4' -chloronicotin anilide was found to be due to the rapid metabolism of the compound in fish to more polar forms which are more easily disposed of-via the bile. Comparison of the relative susceptibilities of two field collections of B. truncatus showed that snails collected from the Frescon--treated area of the Gezira display a higher tolerance to Frescon than do snails collected from the untreated area. Frescon uptake rate was found to be lower in the less susceptible snails, and this is tentatively suggested as the basis of the observed difference in tolerance. It is additionally shown that B. truncatus infected with Schistosoma haematobium is more susceptible to Frescon than uninfected snails.

This thesis is about natural history film-making and how it relates to the public understanding of science. The word 'public' in the phrase is taken to designate in the first place the film-makers. The study is thus one which investigates how natural history film-makers negotiate their identity and situate their knowledge with relation to sciences. Drawing on an examination of the history of the development of natural history film-making in Britain, and on two case studies of contemporary examples of natural history films, this thesis first suggests that the culture of natural history film-making should be regarded as an offshoot of the Victorian culture of amateur natural history, thus as a form of knowledge production in its own right, instead of a form of popularisation of science. In this perspective, natural history film-makers appear as spokespersons for nature and not for science. Their relationship to scientific practitioners would be aptly described as one of co-existence on either side of a border, peopled with such objects as animals, plants, and the motion-picture camera. Natural history film-makers' cognitive authority stems from their status as amateurs naturalists-deriving their knowledge of the natural world from their capacity to engage intimately with it-as well as from their ability to use the film-making apparatus convincingly. The types of evidences supporting the claims to trustworthiness to be observed in natural history films do not appear to relate to the values and beliefs of professional science but to the culture of amateur natural history and to the conventions of the film medium. In order to account for the type of authority to speak for nature embodied in the culture of natural history film-making, this thesis proposes to use the word "telenaturalist".