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The evolutionary biology of Pierinae is described in three separate studies. In Part One, the population biology of the Orange Tip butterfly (Anthocharis card amines) is described. Colonies of this species are localised in riverbank habitats in Co. Durham. Using mark-recapture studies, the population size and movements of individual males were assessed. Studies of individual pre-adult survival indicated that food-plant related mortality and parasitisation were important causes of death. However a key-factor analysis for one population showed that failure of adult females to lay all their eggs was" the most Important factor influencing population size. The adaptiveness of oviposition behaviour was examined by following individual females and by mapping the distribution of eggs upon foodplants. It was shown that many aspects of oviposition choice were best interpreted as chance outcomes of searching behaviour. The observed differences in larval survival on different foodplants, and the constraints placed by time shortage on oviposition were used to construct a simple optimality model. It was shown that oligophagy, the typical condition of A. cardamines populations, leads to increased individual fitness when compared to monophagy. The effect of this stabilising selection on future speciation in Pierinae is discussed. The concept of effective population size is developed for A. cardainines and it is shown that allelic variation at one locus conforms to the predictions of sampling theory in small populations. Part two describes the mating behaviour of several Pierinae, and demonstrates that reproductive isolation in this group is not a result of male behaviour, but of female discrimination of male characters. The agreement of observed behaviour with the predictions of sexual selection is noted, and the likely effects of sexual selection in past and future speciation is discussed. Part three describes the amount of structural gene change that has occurred during the evolution of Pierinae It is shown that little genetic differentiation at such loci occurs prior to or during speciation. Rather, differentiation of species appears to occur at other loci, including those involved in local adaptation, as was described for montane and lowland populations of the Green-Veined White butterfly (Artogeia napi) in Co. Durham. The importance of these results to the wider field of speciation studies is discussed.

This thesis compares the rheology of unspun silk from both the spider and the silkworm in order to understand their evolutionary constraints and to turn these into design criteria for artificial silks.

In this thesis the diversity and ecology of the Lepidoptera fauna of the Galapagos Islands, Ecuador are investigated. The study covers aspects of Lepidoptera diversity, their interactions with host plant and their seasonality. Diversity: The Galapagos Lepidoptera fauna is characterized by low diversification, a high level of endemism and prolonged geographic isolation. To date, 313 species of Lepidoptera are known to occur on the Archipelago and 64% of the native component of this fauna is endemic. Humans have introduced 62 species accidentally to the Islands. All Galapagos Lepidoptera are of American origin except the few introduced Old World species that are nearly cosmopolitan. Host plant relationships: Host plant data covering 155 species Galapagos species are reviewed, and new records of larvae of 113 species collected in the study area are presented. Most of the species are herbivores (272), with a few detritivores (13) and carnivores (3). Plants of the families Leguminosae and Asteraceae are the most common hosts for Galapagos species. Monophagy at the plant family level appears to be widespread in Galapagos Lepidoptera. Seasonality: The phenology of adult Sphingidae was studied at one locality in the arid zone of the southern slope of Santa Cruz Island, Galapagos for a period of 28 months (April 1999--August 2001). A total of 14 species, representing eight genera, was recorded during this study period. Sphingidae moths were more abundant in the wet season (December-May) with peaks occurring mid season. The number of specimens recorded decreased in the dry season (June-November) with the lowest numbers found in August. The seasonality and temporal stability (in terms of species diversity, population abundance and niche breadth) of this community is analysed.

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An autecological study of Thecla betulae L. and Strymonidia pruni L. has been made to discover why these closely related butterflies should be so local and rare when the foodplant of both, Prunus spinosa L. is so widespread and common. Information was also required to formulate conservation plans for both insects. The distribution and status, habitat characteristics, general biology and behaviour, and population dynamics of each species was studied from 1969 to 1973. T. betulae was found to be widely distributed throughout southern Britain, but to be very local. In some regions it has declined considerably in the last 100 years. Most colonies are on lowlying soils, especially clays, and most are near woods. T. betulae oviposits near the ground along wood edges and especially hedges, although there is some evidence that adults require woods, where they aggregate. The population dynamics of a colony of T. betulae at Cranleigh, Surrey was studied for four years. The heaviest mortalities occurred in the pupal stage probably due to predation by small mammals. The failure of females to lay their full potential of eggs was also important in regulating numbers. This appeared to be dependent on the length of time females were on the site, but climatic conditions were also important. S. pruni is restricted to the east Midlands in England where it has been recorded from about 50% of the larger woods on the lowlying land between Peterborough and Oxford. These are mostly on clays. S. pruni colonies usually occur within woods or along sheltered edges. They are very local and the adults rarely stray, so that colonisation of new habitat appears to be very slow. This is probably a major reason why S. pruni is so local, for colonies can only survive very gradual forestry operations and it is only in the east Midlands in Britain that coppice cycles have been long for several centuries. Recent changes in forestry practices have destroyed several colonies. At Monks Wood heavy mortalities were found in the late larval and pupal stages of S. pruni and attributed to bird predation. There is evidence that the temperature during these stages (in May and June) indirectly affects adult numbers.

Insects are inherently unstable and therefore rely on sensory feedback in order to maintain flight control and stability. This thesis focuses on how the hawkmoth Manduca sexta uses visual feedback to control and stabilise flight. The analysis is based on extensive sampling of the optomotor responses. I use a virtual reality flight simulator to measure the total moment that the moths generate in response to oscillating wide-field stimuli. The visual stimuli simulate rotations of different amplitudes and frequencies about six different body axes. The moment responses depend upon stimulus amplitude, so are fundamentally non-linear. Nevertheless, for a fixed and suitably small stimulus amplitude, it is possible to fit a linear PID-controller with time delay to each of the optomotor responses. The analysis shows that the moths rely on proportional and integral feedback of angular velocity, with different time delays about different rotation axes. This varying time delay prevents spatial superposition of the optomotor responses to lateral rotational stimuli, meaning that there is no general control law that predicts the responses to an arbitrary lateral stimulus. By combining these empirically derived vision-based flight controllers with linearised flight dynamic models of hovering M. sexta, I evaluate their performance in providing flight stability. This analysis suggests that visual feedback is sufficient to stabilise disturbances associated with rotational stimuli about the horizontal roll and dorso-ventral axes, but is insufficient to stabilise disturbances associated with rotational stimuli about the pitch axis, vertical yaw axis, and longitudinal body axis. The time delay of the optomotor response has a substantial influence on the superposition of the measured optomotor responses, and strongly affects the predicted flight stability. The findings presented in this work have implications for understanding not only the mechanisms and functionality of flight control in hawkmoths, but also the results of past and future investigations into vision-based flight control in insects and flapping-wing air vehicles.

Revolutions in sequencing technology have provided an unprecedented opportunity to uncover the genetic basis of traits of adaptive importance, enabling researchers not only to merely describe the means of inheritance of traits but also to establish the genetic changes under selection. This thesis examines the loci involved in two recent episodes of strong selection, namely the suppression of Wolbachia-induced male-killing in the butterfly Hypolimnas bolina and the evolution of melanism in moths. H. bolina has evolved the ability to suppress the male-killing effects of the heritable endosymbiont Wolbachia. This thesis demonstrates firstly that this results from a single locus trait that doesn't involve genetic variants beyond chromosome 25. This simple genetic basis explains in part the speed of spread of the suppressor in natural populations. The hypothesis that the insect sex determination gene doublesex is the target of selection is then examined. Compatible with this hypothesis, doublesex variants were found to cosegregate with suppression, and that the peak of a selective sweep is located within doublesex region. An unusual pattern of inheritance was uncovered at the doublesex locus, suggestive of a duplication event. These data are consistent with, though not proof of, Wolbachia driving the evolution of this key sex determination gene. The progression of a selective sweep for the suppression, as it travelled in space across Independent Samoa, was then examined. The sweep across Independent Samoa corroborated the genomic region immediately around doublesex as the target of selection. The sweep was very broad but weakened as it progressed across Samoa. The thesis then examines the genetic basis of melanism in Lepidoptera, and compares the genomic region associated with a naturally selected melanistic form to a laboratory mutant. The 'natural' example corresponded to a known genomic hotspot for colour pattern evolution, whereas this region was excluded in the laboratory mutants. These data support the pleiotropic view of convergence - that involvement of a single region is associated with minimized non-target effects. The thesis ends with a discussion of these data and a programme for future research in the area.

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