Many species use visual features to avoid predation by several methods, such as concealing themselves, deceiving predators and hindering capture. One of the most striking strategies is aposematism, or warning coloration, in which prey use conspicuous visual signals to advertise chemical or physical defences, and thereby deter predators from attacking. My thesis focuses on the form of these warning signals, namely which elements of visual patterns might be most effective in generating predator avoidance, as well as how these different visual features relate to defence levels and ultimately to prey survival in the wild. To address these issues, I studied the warning signals of Lepidoptera and in particular burnet moths (Zygaenidae: Zygaeninae), day-flying moths with distinctive red and black wings and the remarkable ability to both synthesise defensive compounds and sequester them from their host plants. Technological advances and a growing understanding of animal vision mean that animal signals can be studied in an increasingly precise and ecologically-relevant way. Throughout this thesis, I use sophisticated methods to quantify both the defensive chemicals and wing coloration of burnet moths, as perceived by their avian predators. I examine the key features of day-flying defended Lepidoptera, then focus on the potential for quantitative signal honesty in burnet moths. I explore the relationship between defence levels and measures of coloration, both within the six-spot burnet moth, Zygaena filipendulae, and across species in the Zygaenidae, then test the effects of variation in warning signals on predation risk for artificial burnet-like prey in the field. My work highlights some of the complicating factors that should be accounted for in the study of warning coloration, especially when investigating the potential for quantitative signal honesty. I hope my thesis will provide a basis for future research on the defensive strategies of day-flying moths and inspire others to pursue investigations into aposematism in the Zygaenidae.

A decline in biodiversity in agricultural landscapes has been reported for decades. One of the most important habitats for biodiversity in agricultural landscapes is semi-natural grasslands. To preserve species-rich semi-natural grasslands, research need to focus both on local habitat quality and on landscape composition at various scales. In the current study I examined how nectar sources, host plants and other environmental parameters affected the occurrence of adults of four burnet moth species, residents of semi-natural grasslands. Also, I investigated the effects of landscape composition at 34 spatial scales. The results in general showed positive effects of host plants cover, nectar sources abundance, dry soil, sun exposure, tall sward height, small herb and grass cover. At the landscape level all the species responded negatively to the amount of arable land and positively to the amount of forests at scales up to 10000 m. Two species were negatively affected by the amount of artificial surfaces and pasture at some scales. Though the amount of semi-natural grasslands and patch area did not affect the occurrence of the species, at the local scale semi-natural grasslands were still important for the species. Thus, my results suggest that management should be focused both on local and landscape levels. Focus should be to preserve sunny and open areas of high-quality semi-natural grasslands rich in burnet moths’ host plants and especially nectar sources that seem to be more important than host plants for adults. Semi-natural grasslands should be preferably adjacent to forests and not arable land.

<p>Three species of burnet moths (<em>Zygaena</em> <em>filipendulae</em>,<em> Z</em>. <em>lonicerae</em> and <em>Z</em>. <em>viciae</em>) were studied on the Baltic island Öland, Sweden, in order to reveal the habitat requirements of different life stages. Larvae were found among a higher cover of their most important host plant, <em>Lotus corniculatus</em>, <em>Trifolium medium</em>/<em>pratense </em>or<em> Vicia </em>spp., than were pupae or imagines, and were also observed on plants larger than randomly examined plants. Imagines actively selected nectar plants of <em>Centaurea </em>and <em>Cirsium</em>, growing in sunny conditions, but other red and violet Asteraceae flowers were also favoured. Pupae of <em>Z</em>.<em> filipendulae</em> appeared in taller vegetation than larvae and imagines, probably because the cocoons are spun high on stems of grasses and other plants. The chance of finding such suitable substrates rises with increasing vegetation height. A large scale analysis of occupancy patterns was also made, evaluating the relationship between burnet presence or absence and the area of meadows and pastures within 10 x 10 km grid cells in southern Sweden. All three species showed a positive relationship with increasing area of semi-natural grassland. Thresholds for the amount of habitat, below which the likelihood of occurrence declined more rapidly, could be distinguished around a 40-50 % probability of occurrence. Conservational work should aim at preserving and restoring open and sunny areas, rich in the respective host plants and nectar sources, but vegetation management must be executed with great care or late in the season to not harm unhatched pupae and to maintain substrates suitable for <em>Z</em>. <em>filipendulae</em> pupation.</p>

Three species of burnet moths (Zygaena filipendulae, Z. lonicerae and Z. viciae) were studied on the Baltic island Öland, Sweden, in order to reveal the habitat requirements of different life stages. Larvae were found among a higher cover of their most important host plant, Lotus corniculatus, Trifolium medium/pratense or Vicia spp., than were pupae or imagines, and were also observed on plants larger than randomly examined plants. Imagines actively selected nectar plants of Centaurea and Cirsium, growing in sunny conditions, but other red and violet Asteraceae flowers were also favoured. Pupae of Z. filipendulae appeared in taller vegetation than larvae and imagines, probably because the cocoons are spun high on stems of grasses and other plants. The chance of finding such suitable substrates rises with increasing vegetation height. A large scale analysis of occupancy patterns was also made, evaluating the relationship between burnet presence or absence and the area of meadows and pastures within 10 x 10 km grid cells in southern Sweden. All three species showed a positive relationship with increasing area of semi-natural grassland. Thresholds for the amount of habitat, below which the likelihood of occurrence declined more rapidly, could be distinguished around a 40-50 % probability of occurrence. Conservational work should aim at preserving and restoring open and sunny areas, rich in the respective host plants and nectar sources, but vegetation management must be executed with great care or late in the season to not harm unhatched pupae and to maintain substrates suitable for Z. filipendulae pupation.