The behavioural responses of aphid parasitoids (Hymenoptera: Braconidae: Aphidiinae) to aphid sex pheromones were investigated in the laboratory and field. In a wind tunnel bioassay, Aphidius eadyi, Aphidius rhopalosiphi, Diaeretiella rapae, Ephedrus plagiator, Praon myzophagum and Praon volucre responded to the aphid sex pheromone components nepetalactone and nepetalactol. P. myzophagum reared on two different host aphid species showed different responses to combinations of nepetalactone and nepetalactol in the wind tunnel, indicating that long term laboratory rearing may influence parasitoid responses to aphid sex pheromones. The ability of two aphid parasitoids to learn aphid sex pheromones through prior exposure in the presence of host aphids was investigated. The generalist E. plagiator showed evidence of associative learning, whereas the specialist Aphidius ervi did not. When A. ervi was exposed to the pheromone without contact with host aphids, the parasitoid response was reduced by habituation. Exposure to aphid sex pheromone during laboratory host attack trials had no effect on the host attack behaviour of A. ervi. In laboratory cage experiments, aphid sex pheromone lures increased the retention of A. rhopalosiphi, but not by Praon volucre, on aphid-infested plants. In a wind tunnel bioassay, aphid sex pheromone enhanced the attraction of A. ervi to a plant-host complex. In the field, aphid sex pheromone lures increased parasitisation rates by A. rhopalosiphi and P. volucre on aphid-infested potted plants. A series of potted plant experiments indicated that the pheromone may increase parasitisation of aphids by A. rhopalosiphi, but not P. volucre, at a distance of 1m away from the lure. The effect of baiting plots of winter wheat with aphid sex pheromone was investigated in two field experiments. In 1996, the number of parasitoid mummies was higher in baited plots than in unbaited plots, and the synchrony between aphid and parasitoid populations was closer in baited plots. In 1997, aphid sex pheromone had no effect on parasitisation levels. The results are discussed in the context of developing a novel aphid control strategy based on the use of aphid sex pheromones to manipulate parasitoid populations.

The ecology of Austropotamobius pallipes (Lereboullet) from Markfield Quarry and the River Leen was described. Studies included: 1. Biology. (i) Timing of life cycle events. They related to ambient conditions, especially temperature. (ii) Fecundity. Individual fecundity increased with female size. Population fecundity related to population density. (iii) Local distribution. This related to hide availability. Gross water quality affected the distribution of the river crayfish. 2. Population dynamics. (i) Population size/density. That of the Quarry was greater, and related to hide availability. Seasonal variations in population size were temperature dependent. (ii) Population structure. - size structure varied between populations due to collection techniques. It varied seasonally due to recruitment and differential catchability of certain sub-populations. - sex ratios varied seasonally due to reduced foraging by ovigerous females. - disease and damage occurred for all sizes/sexes. Thelohania contejeanii was absent from Markfield Quarry but increased in the Leen during the study period. 3. Growth. (i) At moulting. Sexual differences were absent for the absolute increment, but males grew quicker due to greater moult frequencies. Growth rates of river animals were greatest due to a longer growing season and smaller population density. (ii) Relative growth of body parts. No consistent population differences occurred, but of significance were chelae and rostrum sizes. Sexual dimorphism occurred for certain variables, notably the chelae and abdomen width. The effects of cadmium and Lindane upon A. pallipes were examined. Studies included: 1. Survival. Juveniles were 10 times more sensitive than adults. Lindane was the most toxic. 2. Uptake and depuration. Cadmium accumulated chiefly in the gills. Some evidence for its translocation to other tissues was found. No sexual differences occurred. Lindane accumulated chiefly in the hepatopancreas. Evidence for its translocation and depuration was shown. No sexual differences occurred. 3. Tissue oxygen consumption. Both toxicants caused a depression. Recovery occurred with time. The results were related to the levels of toxicant in Midlands waters.

This study investigated how the predicted increase in global temperature would affect the interaction between the cereal aphid, Sitobion avenae F. (Hemiptera: Aphididae), and its coccinellid predator, Coccinella septempunctata L. (Coleoptera: CoccinelIidae). A model describing the summer population dynamics of S. avenae (Carter et al., 1982) was modified and updated. New equations describing the dependence of aphid development and reproduction on temperature were formulated. A new submodel, describing the population dynamics of C. septempunctata, was incorporated into the model. The predatory interaction between C. septempunctata and S. aveizae was described using a modified form of the temperature-mediated functional response equation proposed by Mack et al. (1981). A sensitivity analysis showed that the output of the model, which compared well with field observations, was not greatly affected by small changes to the parameters of the equations used in the submodel. Stochastic elements were incorporated into the model; aphid and coccinellid immigration were simulated by sampling randomly from distributions fitted to observed patterns of immigration. Three temperature regimes: hot, moderate and cold, were defined by ranking and splitting the years from 1965 to 1992 according to the mean temperature between April and August. The temperature data from the years assigned to each regime were then used to formulate an equation to describe the daily temperatures within the five months. The model was run for each regime, and the output showed that both coccinellid predation and increased temperatures caused a decrease in aphid abundance. The model also highlighted several more subtle effects of increased temperature on the interaction between S. avenae and C. septempunctata. The importance of the model predictions for future control of aphid populations in cereal crops is discussed.

No description available.

In certain species of cricket and bushcricket (Orthoptera; Ensifera), the male transfers an elaborate spermatophore to the female at mating. This consists of a sperm-containing ampulla and an often substantial, sperm-free, gelatinous mass known as the spermatophylax. After mating, the female eats the spermatophylax before consuming the ampulla. The spermatophylax is particularly well developed in the bushcrickets (Tettigoniidae) and can contribute to a loss of as much as 40% of male body weigh at mating in some species. Recently, there has been considerable debate over the selective pressures responsible for the evolution and maintenance of the spermatophylax and other forms of nuptial feeding in insects. Two different, though not mutually exclusive, functions have been suggested for the spermatophylax: 1) nutrients from the spermatophylax may function to increase the weight and\or number of eggs laid by the female, i.e. may function as paternal investment; 2) the spermatophylax may function to prevent the female from eating the ampulla before complete ejaculate transfer, i.e. may be regarded as a form of mating effort. In this study, a comparative approach combined with laboratory manipulations were used in an attempt to elucidate the selective pressures responsible for the origin, evolutionary enlargement and maintenance (= function) of the spermatophylax in bushcrickets. The results suggest that the spermatophylax originated as an adaptation to maximise ejaculate transfer by countering the tendency of females to eat the ampulla prematurely. The spermatophylax appears to be analogous to a range of adaptations found in males of the sub-order Ensifera, which may be interpreted as functioning to maximise ejaculate transfer. These adaptations include prolonged copulation following spermatophore transfer, feeding the female with glandular secretions following spermatophore transfer, post-copulatory mate guarding and multiple copulations with the same female. The occurrence of prolonged copulation following spermatophore transfer appears to be associated with the total loss of the spermatophylax in the meconematine bushcricket Meconema and with the considerable reduction in spermatophylax size in the ephippigerine bushcricket Uromenus rugiscollis. This supports the hypothesis that prolonged copulation and the spermatophylax are analogous in function. The subsequent evolutionary enlargement of the spermatophylax appears to have accompanied the evolutionary enlargement of ejaculate volume and sperm number, i.e. appears to have proceeded to facilitate the transfer of larger ejaculates. A comparative study of 43 species of bushcricket revealed a positive relationship, across taxa, between evolutionary changes in spermatophylax size and changes in ampulla size (i.e. ejaculate volume) and sperm number, with male body weight controlled for. The current function of the large spermatophylax appears to be the same as that of the small spermatophylax, i.e. to ensure complete sperm \ ejaculate transfer. No significant difference in the shape of the sperm transfer curve relative to the mean duration of spermatophylax consumption was found between Leptophyes punctatissima (small spermatophylax) and L.laticauda (large spermatophylax). Furthermore, in L.laticauda, males appear to adjust the size of the spermatophylax in relation to the amount of sperm or volume of ejaculate they are able to produce: a positive relationship was found between spermatophylax mass and sperm number and between spermatophylax mass and ampulla mass (i.e. ejaculate volume). The possibility that the spermatophylax additionally functions as paternal investment cannot, however, be ruled out on this basis. In order for male-donated nutrients to function as paternal investment they must 1) have a positive effect on offspring fitness and\or number and 2) the nutrient donating male must stand to fertilise most or all of the offspring which benefit from his nutrients. A positive effect of spermatophylax consumption on egg weight and\or number has previously been documented in some species of bushcricket, though has not been found in others. In this study, no effect of spermatophylax consumption on female reproductive output was found in L.punctatissima, L.laticauda, or Steropleurus, even when, in the latter two cases, females were maintained on a restricted diet. Furthermore, in L.punctatissima and Steropleurus stali (though not in L.laticauda) it appears that the spermatophylax-donating male is unlikely to fertilise eggs in which his nutrients might be incorporated, in light of the short female re-mating interval, the pattern of last-male sperm precedence and the pattern of oviposition. The enormous spermatophylax of S.stali is unlikely, therefore, to function as paternal investment. Recent studies suggest that in a number of other bushcricket species, including some with very large spermatophylaxes, the spermatophylax is also unlikely to function as paternal investment for the above reasons. In conclusion, while the paternal investment hypothesis lacks generality, the ejaculate-protection hypothesis seems to be more widely applicable and appears to successfully account for the origin, evolutionary enlargement and current function of the spermatophylax in bushcrickets.

The host-parasite relationship of the hookworm Ancylostoma ceylanicum was explored in a hamster model system, focusing on intestinal mucosal responses to infection. Primary infection induced a rapid reduction in villous height culminating in excess of 75% reduction by day 35. Crypts of Lieberkuhn increased in depth achieving maximum depth by day 35. Mitotic figures in crypts and mast cells increased until day 28. Goblet cells increased continuously from background levels of 50 cell/mm² to exceed 300 cells/mm² by day 42. Paneth cell numbers declined in infected animals. Termination of infection by anthelmintic restored background values of intestinal architecture and goblet cell numbers within 7 days, but mast cells took longer and Paneth cell numbers increased beyond values in naïve controls. Mucosal changes are therefore dependent on the presence of worms, intensity of infection and change dramatically with time. Mucosal changes were studied in hamsters experiencing secondary infections following anthelmintic abbreviation of the immunizing infection, superimposed challenge infection and trickle infections. The kinetics of the responses were compared to animals experiencing primary infections and naive controls. Among the findings were: 1) continuous reduction in villous height and a marked increase in crypt depth from day 10 after challenge in abbreviated primary-challenged hamsters compared to little change in hamsters given superimposed challenge. 2) marked mast, goblet, and Paneth cell and eosinophil responses. 3) less intense mast cell responses in abbreviated primary-challenged compared to superimposed challenge animals 4) after a superimposed challenge poor goblet cell responses because levels were already high at the time of challenge, little change in Paneth cells but intense eosinophil responses 5) slower changes in mucosal architecture and mast cell responses in trickle-infected animals eventually exceeding those in primary infected animals. 6) less marked goblet and Paneth cell responses in trickle-infected groups but more intense, persistent increases in eosinophils Cyclosporin A's (CsA) usefulness as an immunosuppressive therapy for blocking T cell control of immunity was explored. However, CsA turned out to have marked anthelmintic properties and reductions in worm burden confounded the interpretation of mucosal changes.

Multitrophic and intraguild interactions influence the success of biological control. The interactions between Acyrthosiphon pisum, three natural enemies (Pandora neoaphidis, Coccinella septempunctata and Aphidius ervi) and the host plant, Vicia faba, were assessed. Volatiles released from aphid-damaged plants had a direct effect on P. neoaphidis indicating they may act as synomones. However, volatiles did not increase efficacy of the fungus suggesting it is not a bodyguard species. Transmission was greatest during plant colonisation by aphids and was not affected by plant condition. Infection by P. neoaphidis had a direct negative effect on the fitness of the aphid through reduced reproduction and early host death. Avoidance of infected colonies by predators and parasitoids could reduce the effectiveness of guilds of natural enemies for biological control. However, at the laboratory scale A. ervi and C. septempunctata did not detect infection and entered and foraged in infected aphid colonies. Aphidius ervi spent longer searching for hosts on plants that had been damaged by aphid feeding (and were emitting aphid-induced species-specific volatiles) and this may increase fungal transmission. Coccinella septempunctata and A. ervi significantly reduced populations of A. pisum when introduced as individual species whereas P. neoaphidis had no effect on aphid population size. Foraging by both C. septempunctata and A. ervi increased the abundance and distribution of P. neoaphidis which may be sufficient to initiate an epizootic. The benefits of increased transmission by C. septempunctata outweighed the fitness costs to the fungus of intraguild predation. Pandora neoaphidis was associated with a decrease in the reproductive success of A. ervi, which was further reduced as the competitive advantage of the fungus increased. This could result in competitive exclusion of the parasitoid. Poly tunnel experiments confirmed that A. ervi did not discriminate between infected and uninfected aphid colonies at this spatial scale. However, A. ervi did not incur a fitness cost from foraging in patches containing the fungus. These results indicate that C. septempunctata and P. neoaphidis may be effective as multi-species biocontrol agents. In contrast, competition between P. neoaphidis and A. ervi may reduce their overall effectiveness as control agents. Further work is required at larger spatial scales and over several generations of both the pest and natural enemy species to confirm these interactions. The implications of these results for the use of P. neoaphidis as part of a multi-species biological control program are discussed.

Freshwater planarian Schmidtea mediterranea is an emerging model for studying in vivo gene functions and regulation in native cell niches. The obligate asexual strain of this species reproduces by fission, in which succession of soma occurs without passing through the germline. To achieve this somatic immortality the somatic stem cells need to overcome the end replication problem. Therefore it can be hypothesised that somatic telomere maintenance in asexual S. mediterranea must possess a germ-like property, with which age-related erosions can be adequately repaired. In this PhD project, the telomere repeat unit in S. mediterranea was confirmed to be the vertebrate-like TTAGGG. Attrition of whole body telomere length was found in ageing sexual worms and also in asexual worms which had not gone through recent fission events. Opposite telomere length dynamics were observed in regenerated samples of the two strains, with erosion in the sexuals and reset in the asexuals. The telomere maintenance was found to increase during regeneration in both strains, with a higher level of increase in asexual worms. A homolog of the telomerase reverse transcriptase subunit, Smed_Tert, was identified and characterised in this organism. High level of Smed_Tert expression was seen in germ cells in mature sexual worms and adult stem cells in asexual worms. Knockdown of Smed_Tert expression by RNA interference caused progressive telomere erosion, however effects on cell proliferation and viability have not been observed in knockdown samples. Four alternate splice isoforms of Smed_Tert were identified. The enhanced telomerase activity during regeneration correlates with a proportional increase in the full-length isoform and a decrease in isoforms with a truncated TRBD domain, suggesting a dominant negative regulation of telomerase by alternative splicing. Significant increase in the expression of the full-length isoform was seen in regenerating asexual samples but not in sexual strains, which correlates with their telomere length dynamics. It is hoped that the comparative studies between the sexual and asexual strains can improve our understanding of how soma can evolve to become an effective inheritable unit.

During development, polarity is a common feature of many cell types. One example is the polarisation of whole fields of epithelial cells within the plane of the epithelium, a phenomenon called planar cell polarity (PCP). It is widespread in nature and plays important roles in development and physiology. Prominent examples include the epithelial cells of external structures of insects like the fruit fly Drosophila melanogaster, polarised tissue morphogenesis in vertebrates and sensory hair cells in the vertebrate ear. In this work we focus on the wing and the abdomen of Drosophila, where PCP becomes obvious in the alignment of hairs and bristles. The underlying dynamics are not fully understood yet, but two distinct protein networks centred around the transmembrane proteins Frizzled and Dachsous, respectively, have been shown to play essential roles. We will present and analyse five models for different aspects of the process of planar cell polarisation. The first two models assess the nature of PCP in a generic setting, ensuring that the results are valid for whole classes of PCP models. Models three and four are existing more complex models that include detailed assumptions about the underlying protein interactions of the Frizzled system in the Drosophila wing. Model five considers the Dachsous system in the Drosophila abdomen. We describe the features of the different types of mechanisms and determine the conditions under which they can yield polarity. All five models can establish wild-type polarity for a wide range of parameter values. We find, however, that for model one, three and four an inhomogeneous pattern exists for the same parameter values as the polarised state. Therefore, in these cases either specific initial conditions, which are unlikely in nature, or a global bias are necessary to ensure correct polarisation. Furthermore, we present the effects of clonal clusters of cells on the polarity of the surrounding cells in our models and relate them to the phenotypes observed in experiments. Model one and five show the largest discrepance between the numerical and the experimental results. We discuss the biological relevance of these findings and indicate outstanding questions.

Acanthamoeba castellanii is an amoeboid protozoan which causes opportunistic infections, including granulomatous encephalitis in immune-compromised patients. Haematogenous dissemination follows initial infection and the pathogen exhibits an ability to cross the blood-brain barrier (BBB). In the bloodstream and at the site of BBB penetration in the brain microvasculature A. castellanii is exposed to host humoral immunity. Here, we have provided insights into A. castellanii pathogenesis and the identity of amoeba antigens participating in immune control. We have investigated the role circulating immunoglobulin plays in preventing penetration of the BBB, and whether trophozoites can alter the efficacy of the immune response. Furthermore we have extended previously published data, demonstrating that amoeba proteases can degrade all antibody classes including physiologically-derived antibody. Nonspecific binding of polyclonal antibody was also observed, and attributed to Fc-binding activity by trophozoites. Additionally, we have examined the binding dynamics of A. castellanii under physiological conditions. BBB disruption was shown to be not directly linked to binding, instead it is reliant on secreted proteases. This study provides insights into mechanisms by which A. castellanii evades host immunity and crosses the BBB. This has the potential to enhance therapeutic strategies aimed at restoring essential disease prevention processes. In addition we have identified a number of amoeba antigens that are targets for the immune system and which may therefore be exploited through vaccination or immunotherapy.