The bacterium Xenorhabdus nematophilus depresses nodulation reactions to infection by inhibiting eicosanoid biosynthesis in tobacco hornworms, Manduca sexta.

The bacterium, Xenorhabdus nematophilus, is a virulent insect pathogen. We tested the hypothesis that this bacterium impairs insect cellular immune defense reactions by inhibiting biosynthesis of eicosanoids involved in mediating cellular defense reactions. Fifth instar tobacco hornworms, Manduca sexta, produced melanized nodules in reaction to challenge with living and heat-killed X. nematophilus. However, the nodulation reactions were much attenuated in insects challenged with living bacteria (approximately 20 nodules/larva for living bacteria vs. approximately 80 nodules/larva in insects challenged with heat-killed bacteria). The nodule-inhibiting action of living X. nematophilus was due to a factor that was present in the organic, but not aqueous, fraction of the bacterial cultural medium. The nodule-inhibiting factor in the organic fraction was labile to heat treatments. The immunodepressive influence of the factor in the organic fraction was reversed by treating challenged hornworms with arachidonic acid. The factor also depressed nodulation reactions to challenge with the plant pathogenic bacteria, Pseudomonas putida and Ralstonia solanacearum. These findings indicate that one or more factors from X. nematophilus depress nodulation reactions in tobacco hornworms by inhibiting eicosanoid biosynthesis.

In-field labeling of western corn rootworm adults (Coleoptera: Chrysomelidae) with rubidium.

Field and laboratory studies were conducted in 2000 and 2001 to determine the feasibility of mass marking western corn rootworm adults, Diabrotica virgifera virgifera LeConte, with RbCl in the field. Results showed that application of rubidium (Rb) in solution to both the soil (1 g Rb/plant) and whorl (1 g Rb/plant) of corn plants was optimal for labeling western corn rootworm adults during larval development. Development of larvae on Rb-enriched corn with this technique did not significantly influence adult dry weight or survival. Rb was also highly mobile in the plant. Application of Rb to both the soil and the whorl resulted in median Rb concentrations in the roots (5,860 ppm) that were 150-fold greater than concentrations in untreated roots (38 ppm) 5 wk after treatment. Additionally, at least 90% of the beetles that emerged during the first 3 wk were labeled above the baseline Rb concentration (5 ppm dry weight) determined from untreated beetles. Because emergence was 72% complete at this time, a significant proportion of the population had been labeled. Results from laboratory experiments showed that labeled beetles remained distinguishable from unlabeled beetles for up to 4 d postemergence. The ability to efficiently label large numbers of beetles under field conditions and for a defined period with virtually no disruption of the population provides an unparalleled opportunity to conduct mark-recapture experiments for quantifying the short-range, intrafield movement of adult corn rootworms.

Eicosanoids in Insect Biology / Eicosanóides na Biologia de Insetos

Prostaglandinas e eicosanóides relacionados são metabolitos oxigenados de certos ácidos graxos poli-insaturados C20 . Eicosanóides são melhor entendidos em relação à sua significância clínica em medicina humana. Sugerimos um novo e mais amplo significado para os eicosanóides, o qual chamamos 'paradigma biológico'. Sob esse aspecto, notamos que eicosanóides desempenhavam funções como sinalizadores celulares antes da origem dos Metazoa. Durante a diversificação evolucionária dos animais, os eicosanóides têm sido envolvidos em uma serie de funções biológicas, algumas das quais ocorrendo somente em insetos e em outros invertebrados. Essas ações múltiplas dos eicosanóides permitem o melhor entendimento dos fenômenos biológicos. Para desenvolver essas idéias nós revisamos os papéis dos eicosanóides em duas áreas da biologia de invertebrados: mediação das reações da imunidade de insetos a bactérias e interações hospedeiro-parasita. Numa visão ampla, os eicosanóides desempenham importantes funções na organização biológica ao nível das células, dos organismos e das interações ecológicas. Sugerimos que os questionamentos contínuos sobre a significância dos eicosanóides levarão a novos entendimentos na biologia dos insetos.

Prostaglandins and related eicosanoids are oxygenated metabolites of certain C20 polyunsaturated fatty acids. Eicosanoids are best understood in the context of their clinical significance in human medicine. We suggest a new and broader view of eicosanoids, which we have been calling a 'biological paradigm'. Under this view, we note that eicosanoids were taken into roles as cellular signal moieties long before the origins of the Metazoa. During the evolutionary diversification of animals, eicosanoids have been recruited into an array of biological roles, some of which occur only in insects and other invertebrates. These multiple actions endow eicosanoids with unusual explanatory power in understanding biological phenomena. We review the roles of eicosanoids in two areas of invertebrate biology: mediation of insect immune reactions to bacteria and host-parasite interactions. Seen broadly, eicosanoids play important roles at the cellular, organismal and ecological levels of biological organization. We suggest that continued inquiry into the significance of eicosanoids will yield important new insights into insect biology.

Prostaglandin biosynthesis by fat body from larvae of the beetle Zophobas atratus.

We describe prostaglandin (PG) biosynthesis by microsomal-enriched fractions of fat body prepared from larvae of the tenebrionid beetle, Zophobas atratus. PG biosynthesis was sensitive to incubation time, temperature, pH, substrate and protein concentration. Optimal PG biosynthesis conditions of those we examined included 2 mg of microsomal-enriched protein, incubated at 22 degrees C for 2 min at pH 6. These preparations yielded four major PGs: PGA(2), PGE(2), PGD(2) and PGF(2 alpha). PGA(2) and PGF(2 alpha) were the predominant eicosanoids produced under these conditions. Two non-steroidal anti-inflammatory drugs, indomethacin and naproxen, effectively inhibited PG biosynthesis in low concentrations. In vitro PG biosynthetic reaction conditions, using vertebrate or invertebrate enzyme sources, usually include a cocktail of reaction co-factors. The Z. atratus preparation similarly performs better in the presence of co-factors. Arch.