Martin Strausz

PDF der Diplomarbeit im Hochschulschriften-Service der Universität Wien

Habitat and host plant use of the Large Copper Butterfly Lyaena dispar rutilus (Lepidoptera:Lycaenidae) in Vienna (Austria)

This study was designed to investigate egg placement patterns at three different spatial scales for the Large Copper butterfly (Lycaena dispar), a species of considerable conservation interest. In Austria the subspecies L. d. rutilus is bivoltine, with the first generation occurring from the end of May to mid June and the second in August. Females deposit their white eggs onto the leaf surface where they are visually easy to detect. Earlier studies have demonstrated that searching for pre-imaginal stages in Lycaena dispar is a far better way to prove the incidence of this species at particular locations than the observation of adults. Accordingly, this study was based on searching for eggs on appropriate food plants in Vienna. In order to assess the importance of characteristics that influence host plant selection and habitat choice by egg laying females at the site, plant, and leaf scale, different biotic and non-biotic factors were measured. 23 study sites with potential food plants were investigated at the end of the flight period of the two generations of Lycaena dispar rutilus in the year 2008. A total of 2457 eggs and 271 larvae were counted. Most eggs and larvae were encountered at dry fallows and urban waste land. Statistical analyses revealed that on site scale only the landscape zones according to the classification of the Vienna municipality had a significant effect on egg densities. The sparsely or densely built up urban zones harboured nearly half of the whole egg records. Six different Rumex species were confirmed as host plants for Lycaena dispar rutilus in Vienna, two of which had not been mentioned as food plants for this species in the literature. Rumex crispus was found to be the most abundant and most important host plant for egg-laying females of both generations harbouring 87.55% of the total number of egg counts. Rumex crispus (4.4 eggs/plant) was preferred over Rumex obtusifolius for oviposition (1.1 eggs/plant). At the plant scale more eggs were found on higher plants and on plants with a higher potential daily sunshine duration. Mowing had a significantly negative effect on egg densities at plant level. At the leaf scale tall leaves were preferred by egg laying females. The degree of infection through a phytopathogenic fungus (Uromyces rumicis) did not affected oviposition preference. For the future persistence of the Large Copper Butterfly in Vienna conservation strategies should focus on the maintenance of appropriate habitat patches, i.e. so called “wasteland” like e.g. fallows. Natural succession of such areas should be prevented by extensive management, e.g. by mowing parts of the habitat every 2-3 years. This will not only support the Large Copper but also many other threatened insects.

Die Diplomarbeit wurde mit dem Wissenschaftlichen Förderpreis 2010 der Wiener Umweltschutzabteilung (MA 22) auszgezeichnet!