TY - JOUR A1 - Obermaier, Elisabeth A1 - Heisswolf, Annette A1 - Randlkofer, B. A1 - Meiners, T. T1 - Enemies in low places - insects avoid winter mortality and egg parasitism by modulating oviposition height N2 - Oviposition site selection in insects is essential in terms of low egg mortality, high offspring survival and therefore a high reproductive output. Although oviposition height could be a crucial factor for the fitness of overwintering eggs, it has rarely been investigated. In this study the oviposition height of a polyphagous leaf beetle, Galeruca tanaceti Linnaeus in different habitats and at different times of the season was examined and its effect on egg clutch mortality was recorded. The leaf beetle occurs as an occasional pest on several agricultural plants. It deposits its eggs within herbaceous vegetation in autumn. Eggs are exposed to numerous biotic and abiotic mortality factors summarized as egg parasitism and winter mortality. Oviposition height of the leaf beetle was not uniform, but changed significantly with the structure of the habitat and during the season. Mean oviposition height per site (70.2±4.9 cm) was significantly higher than mean vegetation height (28.4±2.4 cm). Height of plants with egg clutches attached and oviposition height were significantly positively correlated. The results suggest that females try to oviposit as high as possible in the vegetation and on the plants selected. In accordance with this, the probability of egg parasitism and of winter egg clutch mortality significantly declined with increasing oviposition height. A preference of G. tanaceti for oviposition sites high up in the vegetation might therefore have evolved due to selection pressures by parasitoids and winter mortality. KW - abiotic factors KW - Chrysomelidae KW - enemy free space KW - Galeruca tanaceti KW - oviposition site KW - plant-animal interactions KW - Oomyzus galerucivorus Y1 - 2006 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-48200 ER - TY - JOUR A1 - Heisswolf, Annette A1 - Poethke, Hans-Joachim A1 - Obermaier, Elisabeth T1 - Multitrophic influences on oviposition site selection in a specialized leaf beetle at multiple spatial scales N2 - Egg distribution in herbivorous beetles can be affected by bottom-up (host plant), and by top-down factors (parasitoids and predators), as well as by other habitat parameters. The importance of bottom-up and top-down effects may change with spatial scale. In this study, we investigated the influence of host plant factors and habitat structure on egg distribution in the leaf beetle Cassida canaliculata Laich. (Coleoptera: Chrysomelidae), a monophagous herbivore on Salvia pratensis L. (Lamiales: Lamiaceae), on four spatial scales: individual host plant, microhabitat, macrohabitat, and landscape. At the individual host plant scale we studied the correlation between egg clutch incidence and plant size and quality. On all other scales we analyzed the relationship between the egg clutch incidence of C. canaliculata and host plant percentage cover, host plant density, and the surrounding vegetation structure. Vegetation structure was examined as herbivores might escape egg parasitism by depositing their eggs on sites with vegetation factors unfavorable for host searching parasitoids. The probability that egg clutches of C. canaliculata were present increased with an increasing size, percentage cover, and density of the host plant on three of the four spatial scales: individual host plant, microhabitat, and macrohabitat. There was no correlation between vegetation structure and egg clutch occurrence or parasitism on any spatial scale. A high percentage of egg clutches (38–56%) was parasitized by Foersterella reptans Nees (Hymenoptera: Tetracampidae), the only egg parasitoid, but there was no relationship between egg parasitism and the spatial distribution of egg clutches of C. canaliculata on any of the spatial scales investigated. However, we also discuss results from a further study, which revealed top-down effects on the larval stage. N2 - Die Gelegeverteilung herbivorer Insekten kann sowohl durch bottom-up (Wirtspflanzen) und top-down Faktoren (Parasitoide und Prdatoren), als auch durch weitere Habitatparameter beeinflusst werden. Die Bedeutung der bottom-up und top-down Einflüsse kann zusätzlich von der räumlichen Skala abhängen. In dieser Studie untersuchen wir den Einfluss von Wirtspflanzenfaktoren und der Vegetationsstruktur auf die Gelegeverteilung des Blattkäfers Cassida canaliculata Laich. (Coleoptera: Chrysomelidae), einem auf Salvia pratensis L. (Lamiales: Lamiaceae) monophagen Herbivoren, auf vier räumlichen Skalen: dem Wirtspflanzenindividuum, Mikro- und Makrohabitat, sowie der Landschaft. Auf der Skala des Wirtspflanzenindividuums wurde der Zusammenhang zwischen der Gelegeinzidenz und der Größe und Qualität der Wirtspflanze untersucht. Auf allen anderen Skalen wurde die Korrelation zwischen der Gelegeinzidenz von C. canaliculata und der prozentualen Wirtspflanzendeckung und Wirtspflanzendichte, sowie der umgebenden Vegetationsstruktur analysiert. Die Vegetationsstruktur wurde untersucht, da die Herbivoren ihren Eiparasitoiden entkommen knönten, indem sie ihre Eigelege an Plätzen ablegen, deren Vegetationsstrukturparameter den Eiparasitoiden die Suche erschweren. Die Wahrscheinlichkeit, dass Eigelege von C. canaliculata vorhanden waren, nahm mit zunehmender Größe, prozentualer Deckung und Dichte der Wirtspflanze auf drei der vier untersuchten Skalen zu: Wirtspflanzenindividuum, Mikrohabitat und Makrohabitat. Die Vegetationsstruktur stand jedoch auf keiner räumlichen Skala in einem Zusammenhang mit der Gelegeinzidenz bzw. der Parasitierung der Eigelege. Ein hoher Anteil der Eigelege (38-56%) war durch den einzigen Eiparasitoiden Foersterella reptans Nees (Hymenoptera: Tetracampidae) parasitiert. Es konnte jedoch auf keiner der untersuchten räumlichen Skalen eine Korrelation zwischen der Parasitierung und der räumlichen Gelegeverteilung von C. canaliculata gefunden werden. Wir diskutieren aber auch Ergebnisse einer weiterführenden Studie, in der sich top-down Effekte auf das Larvalstadium zeigten. KW - Eiablage KW - Pflanzenfressende Insekten KW - Eiparasitismus KW - Käfer KW - Chrysomelidae KW - egg parasitism KW - herbivore KW - hostparasitoid interactions KW - plant quality Y1 - 2006 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-47738 ER -