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Ants are one of only four groups which can be classed as being truly social, that is they demonstrate altruistic behaviours towards nestmates. However in order to do this there must be a complex nestmate recognition signal at work. This signal is generally poorly understood, however it is accepted that it makes up a small part of the overall chemical profile present on the cuticle of the ant. This cuticle is coated with a variety of long chain hydrocarbons; the biosynthesis of which is a complex, multi-step process which is generally not well studied in social species. Many of the biosynthetic pathways already discovered have been done so using other insect species which are traditionally easier to work with. Therefore the main aim of this study was to test whether these biosynthetic pathways were also applicable to our studied British ant species. In order to aid the elucidation of the biosynthetic routes, simple feeding experiments were devised. These experiments involved feeding a variety of species of common Britsh ants artificial diets. The species chosen for these experiments belonged to the subfamilies Formicinae and Myrmicinae and the diets were modified by adding an isotopically labelled substrate. The experiments of this type explored the incorporation of these labels into the final biosynthesised hydrocarbon product. Successful incorporation suggested that the substrate was a biologically important molecule to the biosynthetic process; either used as a precursor or later in the biosynthetic process. The results presented within this thesis showed that the incorporation of these labelled substrates depended on a number of factors. The amount of incorporation appeared to vary by species, substrate and label type, as well as possible environmental and instrumental factors such as ant health and instrument sensitivity. It was generally found that the labels based on deuterium atoms were less reliable as their more labile nature meant that any trends were less discernible. More reliable and insightful results were gained when using carbon-13 labels. The incorporation appeared to vary with some species showing different responses to others, however the reasons behind this difference are unknown. It could be down to subtle differences between the biosynthetic pathways or a previously unconsidered factor could be important, such as the health of the colony or rate of hydrocarbon production. The main challenge of this work was sourcing both the correct species of ant, and labelled substrates that were cost effective to use. Custom organic synthesis was used in order to produce a wide range of labelled fatty acids, however ultimately experimental design was dependant on commercial substrate availability. The results shown within this thesis indicate that there is a lot of unknown knowledge surrounding biosynthetic processes in ants and that models gained from other species cannot necessarily be applied to ants. However, it is also clear that there are many possible dependant factors in uencing this work and that far more research needs to be carried out in order to understand the underpinning biosynthetic processes more clearly.

Biological nitrogen fixation (BNF) is a microbial process that fixes atmospheric nitrogen (N2) gas into reactive, bioavailable forms (Nr). Naturally, lightning and BNF accounted for the entire Nr available for plant and microbial metabolic demands. However, following industrialization, Nr has also been produced anthropogenically (e.g. burning fossil fuel, fertilizers). The UK experiences high rates of anthropogenic Nr deposition (>26 kg ha-1yr-1) not being clear if increased Nr deposition slows or shuts down BNF in peatlands and temperate forests, as Nr is freely available. Therefore, it was critical to investigate it. The research objectives were to establish a robust method to measure BNF, to evaluate the impact of chronic Nr deposition on BNF and to examine the main factors controlling BNF. Following comparative evaluation of the two common methods for quantifying BNF in peatlands, the acetylene reduction assay underestimated BNF by 53% compared to the direct 15N2 assimilation method. Across a gradient of Nr deposition, higher rates of in situ BNF were found in areas with lower Nr deposition rates and BNF decreased as Nr increased; however, BNF did not shut down completely. Under experimental long-term addition of Nr and sulphur into a peatland in northern Sweden, BNF decreased by 94%. Sphagnum mosses exposed to higher Nr deposition exhibited an increase in BNF by 83% following the addition of P and K. Addition of microbial respiratory metabolites (CH4, CO2 and N2O) to mosses enhanced BNF 80%. Asymbiotic BNF in deciduous temperate forest soils exposed to ~22 kg Nr annual deposition increased by 368% under elevated CO2 fumigation. This research demonstrates that BNF does not shut down under chronic atmospheric Nr and that increased availability of nutrients and energy for microbes can further boost BNF. Therefore, BNF must be considered even in polluted areas when modelling the N economy of their ecosystems.

Post Mortem Interval (PMI) estimation is a key concern of forensic entomology research. Numerous factors are recognized to affect these calculations, and have shown to potentially introduce error, leading to an incorrect time of death estimation. One such acknowledged factor is the presence of drugs and toxins. A range of Novel Psychoactive Substances (NPS), common adulterants and one illegal drug were tested on two blowfly species, of forensic importance, Calliphora vicina and Lucilia sericata (Diptera: Calliphoridae). An artificial diet was used to enable effective delivery of the substances; the effect on development was studied by observing larval length, weight, instar and time taken to reach pupariation. As a potential alternative for accurate aging, the cuticular hydrocarbon profile was analysed for changes in response to drug presence. Preliminary investigations were also carried out to detect the presence of NPS within larvae, by extraction and derivatisation. The NPS had a profound effect on the development of immature larval samples; rates were mostly accelerated, shown by larval length, weight and an increase in time taken to reach pupariation. A potential PMI overestimation of 48 hours was presented for a number of substances. Paracetamol was the only drug shown to produce developmental delay, up to 48 hours for a higher dose. The effects of drug dosage and potential to use data from chemically similar drugs for PMI estimations are presented; MDA is compared with NPS, 6APB. Noteworthy, the cuticular hydrocarbon profile showed no major changes in response to the drugs, some minor differences were observed but this was less pronounced than the development data and has lesser effect on PMI estimation. Results encourage the use of cuticular hydrocarbon analysis for accurately aging blowfly, despite showing developmental changes triggered by drug ingestion, which may otherwise cause incorrect PMI estimations.