Juvenilhormon-Esterase, ein Schlüsselenzym in Wirt-Parasitoid-Interaktionen

Hymenopteran endoparasitoids that develop inside their lepidopteran host may exert a multitude of interactions with their host until they are able to emerge successfully from a developmentally arrested host that finally dies. Parasitoid interferences comprise physiological and biochemical modifications in the host endocrine and immune system which in turn affect host growth and development (reviewed in Edwards & Weaver, 2001). We use the gypsy moth, Lymantria dispar (Lep., Lymantriidae) and the endoparasitic, polydnavirus (PDV)-carrying braconid wasp Glyptapanteles liparidis (Hym., Braconidae) as a model system to study the endocrine changes associated with parasitism. Following wasp oviposition into young gypsy moth larvae, the parasitoids develop through two endoparasitic instars, and then emerge as newly molted third instars from a host that dies in the larval stage. In previous studies we have already described the endocrine changes in parasitized gypsy moth larvae which show an increase in juvenile hormone (JH) titers, a shift from JH II to JH III as the dominant homologue, and a prominent decrease in the JH degrading enzymes (Schopf & al., 1996; Schafellner & al., 2004). Here, we investigated the possible mechanisms that account for the JH elevating effects such as (i) stimulated host corpora allata activity, (ii) reduced activity of the JH metabolic enzymes such as JH esterase, and (iii) synthesis and release of JH by the parasitoid larvae.Die gregäre, parasitische Brackwespe Glyptapanteles liparidis (Hym., Braconidae) entwickelt sich in den Raupen des Schwammspinners Lymantria dispar (Lep., Lymantriidae). Bei der Eiablage injiziert die Wespe Viruspartikel in die Leibeshöhle der Wirtsraupe, die deren Immunabwehr lahm legen und so das Einkapseln der Eier verhindern. Im Laufe der Entwicklung der Parasitoidenlarven ändern sich die Juvenilhormongehalte in der Wirtshämolymphe dramatisch. Das für den Abbau des Juvenilhormons verantwortliche Enzym, die Juvenilhormon-Esterase (JH-Esterase), wird dramatisch herunterreguliert, während der Titer an Juvenilhormon steigt und kurz vor dem Ausbohren der Parasitoiden das Hundertfache des Normalwertes von unparasitierten Raupen erreicht. Wir konnten in unseren Untersuchungen nachweisen, dass die Polydnaviren für die Blockierung dieses spezifischen Enzyms verantwortlich sind, wobei aber die Aktivität des JH-Esterase Gens in den parasitierten Raupen unverändert bleibt. Mit der Häutung der Parasitoidenlarven in das 2. Larvenstadium beginnt der Hormonspiegel in der Hämolymphe kontinuierlich anzuwachsen. Auffallend dabei ist, dass davon vor allem das JH III Homolog betroffen ist, welches als das bisher einzige von Hymenopteren produzierte Homolog bekannt ist. Mit Hilfe von Inkubationsversuchen konnten wir zeigen, dass dieses Homolog von den Parasitoidenlarven selbst produziert und in die Wirtsraupe abgegeben wird. Die Syntheseleistung und die Abgabe von JH durch die Corpora allata der Wirtsraupe wird durch die Parasitierung dagegen nicht gesteigert; der im Vergleich zu JH III geringere Anstieg von JH II – dem dominierenden Homologon in Lepidopteren – ist offenbar auf die unterdrückte Enzymaktivität zurückzuführen. Aus den vorliegenden Ergebnissen wird klar, dass Parasitoide und Polydnaviren auf unterschiedlichen Ebenen in die Hormonregulation eingreifen und erst das komplexe Zusammenspiel beider eine erfolgreiche Parasitierung ermöglicht

Business Groups in Emerging Markets-Financial Control & Sequential Investment

Business groups in emerging markets perform better than unaffiliated firms. One explanation is that business groups substitute some functions of missing institutions, for example, enforcing contracts. We investigate this by setting up a model where firms within the business group are connected to each other by a vertical production structure and an internal capital market. Thus, the business group’s organizational mode and the financial structure allow a self-enforcing contract to be designed. Our model of a business group shows that only sequential investments can solve the ex post moral hazard problem. We also find that firms may prefer not to integrate.http://deepblue.lib.umich.edu/bitstream/2027.42/57210/1/wp830 .pd

Passion and Purpose: One Student\u27s Journey to Medical School

In a creative essay, a student describes her passion for science and finding a greater purpose in serving people through science—leading her to pursue a medical career

Business Groups in Emerging Markets - Substitutes for Missing Institutions

Abstract: Business groups in emerging markets perform better than unaffiliated firms. We study how business groups can substitute some functions of missing institutions, for example, enforcing contracts. In a two period model, there is no contract enforcement in the first period. The firms within the business group are connected to each other by a vertical production structure, resulting in externalities due to double marginalization, and an internal capital market. Our model derives the sequencing of investments and the credit contract offered by the headquarters that solve the ex post moral hazard problem. Thus, the business group's organizational mode and the financial structure facilitate relational contracting

Play On: The Use of Games in Libraries

The use of games in the library is a currently trending topic of discussion and writing in the Library and Information Science profession. Upon first consideration, gaming may seem to be irrelevant at best and a waste of time and resources at worst. However, gaming does have several significant implications for all types of libraries, including greater exposure to new information technologies and the sense of community that a gaming program can foster. Thus, libraries should seriously consider the benefits of gaming programs and be prepared to carefully develop collection policies and to properly plan gaming opportunities for their patrons. The following literature review highlights how other libraries have accomplished these goals, provides examples of the different types of gaming programs that can be implemented in libraries, and explains the advantages for the library that come with a gaming program

Quality of Institutions, Credit Markets and Bankruptcy

The number of firm bankruptcies is surprisingly low in economies with poor institutions. We study a model of bank-firm relationship and show that the bank’s decision to liquidate bad firms has two opposing effects. First, the bank receives a payoff if a firm is liquidated. Second, it loses the rent from incumbent customers that is due to its informational advantage. We show that institutions must improve significantly in order to yield a stable equilibrium in which the optimal number of firms is liquidated. There is also a range where improving institutions may decrease the number of bad firms liquidated.http://deepblue.lib.umich.edu/bitstream/2027.42/40131/3/wp745.pd

Bank Competition - When is it Good?

The effects of bank competition and institutions on credit markets are usually studied separately although both factors are interdependent. We study the effect of bank competition on the choice of contracts (screening versus collateralized credit contract) and explicitly capture the impact of the institutional environment. Most importantly, we show that the effects of bank competition on collateralization, access to finance, and social welfare depend on the institutional environment. We predict that firms' access to credit increases in bank competition if institutions are weak but bank competition does not matter if they are well-developed

Forgers, connoisseurs, and the Nazi past

The authentication and accurate attribution of art can be a complex issue. Connoisseurship and ethics, politics and the media can get mixed in among the "active ingredients" that can obstruct efforts to correct scholarly misattribution in the sense of having mistaken the work for that of a master. The expertise of forgers Han van Meegeren and Wolfgang Beltracchi went way beyond artistic skill, technical skill, extensive knowledge of art history and the methods employed by the true masters. The connoisseurs who supplied the authentications were giving and receiving something in return, and this caused the ethical lines to blur. Political opportunism enabled van Meegeren to hide his sympathy for the Volkgeist conventions of Nazi art with a clever plot device by which he could demonstrate that he had conned a member of the Nazi elite. The Beltracchis concocted the history of production of a hitherto unknown number of modern art works by linking the fake provenances to pre-packaged narratives that invoked the most sordid elements of the cultural policy of the Third Reich. At their trials, the forgers assumed the role of "masters of ceremonies" who entertained the court staff and spectators. Unsurprisingly, the media conferred folk hero status on them. This article highlights the uncanny parallels and patterns in the art forgery careers of these two forgers, and specifically also in the misattribution of their forged works. Considering how intricate the interdependencies between evidence and beliefs can be, the ethical responsibility of the art trade when forgeries are sold comes into question. More scientific testing continues to expose some of the secrets of master forgers, but no forgery trial, law report, or media report can completely de-contaminate art history. The relevance of information ethics to the study of art history and material culture deserves to be highlighted more frequently

Loving the Unlovable Body in Yamanaka\u27s Saturday Night at the Pahala Theatre

Lois-Ann Yamanaka’s award-winning yet remarkably neglected Saturday Night at the Pahala Theatre (1993) explores female adolescence and coming of age in a rich, polyphonic collection of verse novellas. “Loving the Unlovable Body” focuses on Yamanaka’s treatment of this transition as a fully embodied, fraught, and often painful experience by expicating the uses of several tropes used to express girls’ experiences of their bodies: eating, voice, eyes, fragmentation, and marking/naming. These metaphors contribute to the development of a complex range of possibilities from devastating to hopeful, presented in juxtaposition and interplay, for girls’ relationships to their culturally denigrated bodies and the consequences to their attempts at positive sense of self