Differential effects of jasmonic acid treatment of Brassica nigra on the attraction of pollinators, parasitoids, and butterflies

Herbivore-induced plant defences influence the behaviour of herbivores as well as that of their natural enemies. Jasmonic acid is one of the key hormones involved in both these direct and indirect induced defences. Jasmonic acid treatment of plants changes the composition of defence chemicals in the plants, induces volatile emission, and increases the production of extrafloral nectar. However, few studies have addressed the potential influence of induced defences on flower nectar chemistry and pollinator behaviour. These have shown that herbivore damage can affect pollination rates and plant fitness. Here, we have investigated the effect of jasmonic acid treatment on floral nectar production and the attraction of pollinators, as well as the effect on the behaviour of an herbivore and its natural enemy. The study system consisted of black mustard plants, Brassica nigra L. (Brassicaceae), pollinators of Brassica nigra (i.e., honeybees and syrphid flies), a specialist herbivore, Pieris rapae L. (Lepidoptera: Pieridae), and a parasitoid wasp that uses Pieris larvae as hosts, Cotesia glomerata L. (Hymenoptera: Braconidae). We show that different trophic levels are differentially affected by jasmonic acid-induced changes. While the herbivore prefers control leaves over jasmonic acid-treated leaves for oviposition, the parasitoid C. glomerata is more attracted to jasmonic acid-treated plants than to control plants. We did not observe differences in pollinator preference, the rates of flower visitation by honeybees and syrphid flies were similar for control and jasmonic acid-treated plants. Plants treated with jasmonic acid secreted less nectar than control plants and the concentrations of glucose and fructose tended to be lower than in nectar from control plants. Jasmonic acid treatment resulted in a lower nectar production than actual feeding damage by P. rapae caterpillars

Comparison of thread-cutting behaviour in three specialist predatory mites to cope with complex webs of Tetranychus spider mites

Anti-predator defenses provided by complex webs of Tetranychus mites can severely impede the performance of generalist predatory mites, whereas this may not be true for specialist predatory mites. Although some specialist predatory mites have developed morphological protection to reduce the adverse effects of complex webs, little is known about their behavioral abilities to cope with the webs. In this study, we compared thread-cutting behavior of three specialist predatory mites, Phytoseiulus persimilis, Neoseiulus womersleyi and N. californicus, exhibited inside the complex web of T. urticae. No major difference was observed among them in the basic pattern of this behavior, using chelicerae and palps, and in the number of silken threads severed while moving inside the web. These results and observations suggest that each predator species cut many sticky silken threads to move inside the complex web without suffering from serious obstructio

Curvature Constraints from the Causal Entropic Principle

Current cosmological observations indicate a preference for a cosmological constant that is drastically smaller than what can be explained by conventional particle physics. The Causal Entropic Principle (Bousso, {\it et al}.) provides an alternative approach to anthropic attempts to predict our observed value of the cosmological constant by calculating the entropy created within a causal diamond. We have extended this work to use the Causal Entropic Principle to predict the preferred curvature within the "multiverse". We have found that values larger than $\rho_k = 40\rho_m$ are disfavored by more than 99.99% and a peak value at $\rho_{\Lambda} = 7.9 \times 10^{-123}$ and $\rho_k =4.3 \rho_m$ for open universes. For universes that allow only positive curvature or both positive and negative curvature, we find a correlation between curvature and dark energy that leads to an extended region of preferred values. Our universe is found to be disfavored to an extent depending the priors on curvature. We also provide a comparison to previous anthropic constraints on open universes and discuss future directions for this work.Comment: 5 pages, 3 Figure

Spectroscopy of the 1S0−3P0^1S_0-{}^3P_0 Clock Transition of 87^{87}Sr in an Optical Lattice

We report on the spectroscopy of the $5s^2 {}^1S_0 (F=9/2) \to 5s5p {}^3P_0 (F=9/2)$ clock transition of ${}^{87}{\rm Sr}$ atoms (natural linewidth of 1 mHz) trapped in a one-dimensional optical lattice. Recoilless transitions with a linewidth of 0.7 kHz as well as the vibrational structure of the lattice potential were observed. By investigating the wavelength dependence of the carrier linewidth, we determined the magic wavelength, where the light shift in the clock transition vanishes, to be $813.5\pm0.9$ nm.Comment: 4 pages, 4 figures, submitted to Phys. Rev. Lett. (09/May/2003

Vom Elend der Konjunkturprognosen

Ausgehend von neueren Befunden über die unzureichende Treffsicherheit und zunehmende Verzerrtheit der Konjunkturprognosen des Sachverständigenrats und eines führenden Wirtschaftsforschungsinstituts in den Jahren nach 1989 wird der These nachgegangen, dass staatlich finanzierte Konjunkturforschung gleichwohl privater Konjunkturforschung hinsichtlich Treffsicherheit und Unverzerrtheit überlegen ist. Der zur Überprüfung der These verwendete Datensatz umfasst die Prognosewerte und Prognosefehler von fünf staatlich finanzierten Einrichtungen – vier große Wirtschaftsforschungsinstitute sowie Sachverständigenrat – und von fünf großen Privatbanken, beginnend mit dem Jahr 1989. Die These von der Überlegenheit staatlich finanzierter Konjunkturforschung kann weder in Bezug auf die Treffsicherheit noch in Bezug auf die Unverzerrtheit bestätigt werden. Die insgesamt unzureichende Qualität der Prognosen beider Gruppen bleibt freilich erklärungsbedürftig. Denn die gängigen Apologien – Globalisierung und Wiedervereinigung – halten einer Überprüfung durch die Autoren nicht stand. --