Ant-plant associations in different forests in Venezuela / Associações formiga-planta em diferentes florestas na Venezuela

We evaluated the hypothesis that the abundance and species distribution of two different kinds of myrmecophilous plants is influenced differently by the ant diversity and abundance. In eight different natural forests in Venezuela we estimated the species richness and abundance of plants, ants on the soil and on the canopy, the leaf damage of plants and soil nutrients. The main results of the study show that plants with domatia (PD) and plants with extrafloral nectaries (PEFN) have different relationships with ants and suffer from different ecological constraints. PD attract a more specific group of ants than PEFN. Our results are consistent with the hypothesis that domatia are adaptations that help plants to increase rare nutrient uptake rather than for herbivore defense. We found that PEFN attract a larger variety of ant species than PD, and ant abundance seems to limit the ecological range of PEFN. The attraction of ants as a mechanism to reduce herbivory, as done by PEFN, does not seem to be superior to alternative anti-herbivore mechanisms used by other plants. Contrary to many former studies, we found that ants are generally more diverse on the soil compared to canopies.

Avaliou-se a hipótese de que a distribuição da abundância e o número de espécie de dois tipos diferentes de plantas mirmecófilas são influenciadas diferentemente pela diversidade e pela abundância de formigas. Em oito florestas naturais diferentes na Venezuela nós estimamos a riqueza de espécies e a abundância de plantas, de formigas no solo e no dossel, os danos às folhas e os nutrientes do solo. Os resultados mostram que as plantas com domácias para alojar formigas e plantas com nectários extraflorais (PEFN) têm relacionamentos diferentes com formigas e sofrem confinamentos ecológicos diferentes. As plantas com domácias atraem um grupo mais específico de formigas do que as PEFN. Os resultados são consistentes com a hipótese de que as domácias são adaptações que ajudam a planta a aumentar o acesso a nutrientes escassos para a defesa de herbívoros. PEFN atraem uma variedade maior da espécie de formigas do que as plantas com domácias, e a abundância de formigas parece limitar a escala ecológica de PEFN. A atração das formigas como mecanismo para reduzir a herbivoria, como feito por PEFN, não parece ser superior aos mecanismos alternativos de prevenção de herbivoria usados por outras plantas. Contrário a muitos estudos anteriores, as formigas mostraram-se geralmente mais diversas no solo comparado ao dossel.

Complex patterns in the oil market

El patrón de las series temporales de precios y volúmenes del petroleo crudo Brent vendido en la International Petroleum Exchange (Londres), fue analizado utilizando técnicas de análisis no lineal desarrolladas para sistemas complejos. Los análisis muestran que las variaciones en el índice de precios y volúmenes de petróleo negociados no son aleatorias y difieren entre ellos. Las variaciones en precios son asimétricas respecto al tiempo mostrando mayor probabilidad para descensos grandes en comparación a aumentos de precio. Los valores del índice de precios muestran períodos cortos de tiempo más o menos estables, sugiriendo fuertes restriccionespara cambios de precios pero no para volúmenes

Avaliação do feromônio sexual de Neoleucinodes elegantalis Guenée (Lepidoptera: Crambidae) / Evaluation of sexual pheromone of Neoleucinodes elegantalis Guenée (Lepidoptera: Crambidae)

Foram avaliados os quatro componentes sintéticos identificados no feromônio sexual da broca-pequena-do-tomate, Neoleucinodes elegantalis Guenée (BPT): (E)-11-hexadecenol (E11-16:OH), (Z)-11-hexadecenol (Z11-16:OH), (E)-11-hexadecenal (E11-16:Al) e (E)-11-Acetato de hexadecenila (E11-16:OAc). Testes de campo foram realizados com armadilhas objetivando identificar o composto mais eficaz na captura de machos do inseto e determinar o efeito de concentrações do isômero Z11-16:OH, em mistura com o componente mais eficaz na captura de machos. Em laboratório, foram realizados testes eletrofisiológicos com eletroantenógrafo para monitorar as respostas da antena de machos de N. elegantalis a diferentes concentrações dos componentes. E11-16:OH, na concentração de 100 æg foi o mais eficaz entre os componentes testados do feromônio sexual da BPT. A adição de seu isômero, Z11-16:OH, reduziu a captura de insetos. Obteve-se resposta fisiológica (potencial de ação) a todos os componentes testados. Para E11-16:OH, a intensidade de despolarização da antena aumentou em relação direta com sua concentração, no entanto, para os demais componentes, os quimioreceptores foram sensíveis somente nas concentrações mais altas.

Four synthetic components of the sexual pheromone identified from the small tomato borer Neoleucinodes elegantalis Guenée (BPT) were evaluated: (E)-11-hexadecenol (E11-16:OH), (Z)-11-hexadecenol (Z11-16:OH), (E)-11-hexadecenal (E11-16:Al) and (E)-11-hexadecenyl acetate (E11-16:OAc). Field tests were carried out with traps aiming at identifying the most effective component in the capture of N. elegantalis males, and determining the effect of different concentrations of the isomeric Z11-16:OH, in a mixture with the most effective component, in the capture of the males. In laboratory, electrophysiological tests were carried out with an electroantennograph to monitor the response of the antenna of N. elegantalis males to logarithmic concentrations of the four identified components. E11-16:OH, at the concentration of 100 æg, was the most effective among the tested components of the sexual pheromone of BPT. The isomer of this component, Z11-16:OH, was added and reduced insect capture. Physiological responses to all tested components were registered. E11-16:OH promoted depolarization of the antenna in straight relation with its concentration, while for the others components, the chemoreceptors have responded only to the higher concentrations.

A synergistic aggregation pheromone component in the banana weevil cosmopolites sordidus germar 1824 (Coleoptera: Curculionidae)

Cosmopolites sordidus is an important pest on banana plantations worldwide. The chemistry of the aggregation pheromone of this insect has been recently resolved and here we present the first evidence from field trails that sordidin, a compound from the male releases aggregation pheromone, attracts significant number of weevils only if host plant odors are also present. Sordidin attracts few insects when it is presented without the host plant tissue. However, the attractiveness of host plant tissue increases more than tenfold when it is presented simultaneously with sordidin in field traps. We confirm experimentally that sordidin may be used as part of a system for mass trapping and monitoring this insect.

Oxygen consumption and other psychophysiological variables during an active coping task / Consumo de oxígeno y otras variables psicofisiológicas durante una taréa de desempeño activa

In an attempt to observe the energy demands during the performance of a mental task, whole body oxygen consumption was measured ehile cubjects solved a series of abstract reasoning problems of different levels of difficulty. Simultaneously, cardiovascular activity and peripheral temperature were recorded. The measurement of oxygen consumption failed to indicated any changes in energy requirement related to information processing; but when subjects were classified according to their oxygen consumption during the initial period, a positive correlation between changes in oxygen consumption and performance with the most difficult tasks was observed. Thus, correlations between body oxygen consumption and cognitive work can be appreciated only with very high levels of task difficulty, and when variations due to "stress" are normalized. Almost all cardiovascular measurements were sensitive to the esperimental task, although none responded diferently when the level of dificulty varied. Heart Rate Variability (HRV) showed the most regular and significant pattern of change. Some specific patterns of physiological reactivity emerged in relation to personality and emotional characteristics of the subjects and to the level of cognitive demand. Of special interes is the opposite correlation found oxygen consumption, and extroversion with tasks of medium difficulty