Physical, chemical and biological variability in the Dr. C. Gelsi reservoir(NW Argentine) : a temporal and spatial approach

With the purpose of understanding the phytoplankton dynamics in two vertical profiles of the Dr. C. Gelsi reservoir (Tucumán, Argentina, monthly samplings were conducted from October 1997 to March 1999 in the limnetic zone and at the intersection of the Salí and Tapia tributary. The reservoir was characterized as warm monomictic, with bicarbonate, chloride, sodium, calcium and/or magnesium waters. In both sites total nitrogen concentration was higher than 1 mg/l, whereas that of orthophosphate reached 0.2 mg/l. Out of the eleven organochlorine pesticides analyzed, the presence mainly of lindane and methoxychlor, with higher concentrations in the warm months was confirmed. Bacterial load values were compatible with water quality standards, and variations in the number of actinomycetes colonies in the sediments were correlated, among other parameters, with dissolved oxygen. In the two zones studied a total of 57 phytoplankton taxa, 49 % green algae, 37 % diatoms, 9 % Cyanobacteria and 5 % dinoflagelates, were identified. Central diatoms (Aulacoseira granulata and Cyclotella meneghiniana) prevailed in the phytoplankton and, in a lesser degree, the other groups, low values of specific diversity being obtained. A principal components analysis based on the absolute abundance of species and on some physico-chemical parameters ordinated the samples of the various levels, this abundance being more evident in the limnetic zone. There was also a tendency to the separation of stratifications from the two consecutive years and homogeneity in the samples from the mixing period was noticed. On the basis of the saprobic index, water quality was from β − α-mesosaprobic to α-mesosaprobic.Con el objeto de interpretar la dinámica del fitoplancton en dos perfiles verticales del embalse Dr. C. Gelsi (Tucumán, Argentina), se realizaron muestreos mensuales desde octubre de 1997 a marzo de 1999, en la zona limnética y en la intersección de los tributarios, ríos Salí y Tapia. El embalse fue caracterizado como monomíctico cálido, con aguas bicarbonatadas, cloruradas, sódicas, cálcicas y/o magnésicas. En ambos sitios, la concentración media de nitrógeno total fue superior a 1 mg/l, mientras que la de ortofosfato llegó a 0.2 mg/l. De los once plaguicidas organoclorados analizados se comprobó, principalmente, la presencia de lindano y metoxicloro, con concentraciones más elevadas en los meses cálidos. Los valores de carga bacteriana fueron compatibles con las normas de calidad de agua y las variaciones del número de colonias de actinomycetes en los sedimentos estuvieron correlacionadas entre otros parámetros con el oxígeno disuelto. En las dos zonas estudiadas se identificaron un total de 57 taxones: 49 % algas verdes, 37 % diatomeas, 9 % Cyanobacteria y 5 % dinoflagelados. Las diatomeas centrales (Aulacoseira granulata y Cyclotella meneghiniana) predominaron en el fitoplancton y en menor orden, los otros grupos, obteniéndose bajos valores de diversidad específica. Los análisis de componentes principales basados en la abundancia absoluta de las especies y en algunos parámetros fisicoquímicos, ordenaron las muestras de los distintos niveles, siendo ésta más evidente en la zona limnética. Asimismo, hubo una tendencia a la separación de las estratificaciones de los dos años consecutivos y se observó homogeneidad en las muestras provenientes del período de mezcla. Sobre la base del índice sapróbico, la calidad del agua fue β − α-mesosapróbicas a α-mesosapróbicas

Parasitism and food web structure in defoliating Lepidoptera – Parasitoid Communities on Soybean

Food webs are usually regarded as snapshots of community feeding interactions. Here, we describe the yearly and cumulative structure of parasitoid–caterpillar food webs on soybean in central Argentina, analyzing parasitism rates and their variability in relation to parasitoid diversity and food web vulnerability in the system. Lepidoptera larvae were collected along four seasons from soybean crops and reared in laboratory to obtain and identify adults and parasitoids. Eleven species of defoliating Lepidoptera and ten parasitoid species were recorded. Food web statistics showed rather low annual variability, with most variation coefficients in the order of 0.20 and generality showing the most stable values. Parasitism showed the highest variability, which was independent of parasitoid diversity and food web vulnerability, although parasitism rates were negatively related to parasitoid richness. Our study highlights the need to consider food web structure and variability in order to understand the functioning of ecological communities in general and in extensive agricultural ecosystems in particular.Fil: Avalos, D. S.. Universidad Nacional de Córdoba. Facultad de Ciencias Agropecuarias; ArgentinaFil: Mangeaud, A.. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales; ArgentinaFil: Valladares, Graciela Rosa. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto Multidisciplinario de Biología Vegetal. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Instituto Multidisciplinario de Biología Vegetal; Argentin

Occurrence of top carnivores in relation to land protection status, human settlements and rock outcrops in the high mountains of central Argentina

We evaluated puma (Puma concolor) and culpeo fox (Pseudalopex culpaeus smithersi) occurrence in relation to a national park where livestock was reduced and hunting banned, and in relation to human presence and landscape features. In the high mountains of central Argentina puma signs were about 3.5 times less frequent than culpeo signs. Puma and culpeo signs were 33 and 19 times, respectively, more abundant within than outside the park. Puma signs increased with distance to settlements within the park but no trend was detected outside the park where signs were scarce. Culpeos were abundant all throughout the park with no relation with distance to settlements while outside the park signs increased with distance from settlements. Rock outcrops had a positive effect on pumas, which used this habitat frequently, and negative effect on culpeos, whose presence decreased slightly at sites with the highest proportion of rock outcrops inside the park and sharply at sites with presence of rock outcrops outside the park. We conclude that top carnivores were positively affected by the park creation and encourage the creation of more protected areas with connectivity in the region to better assure the long-term conservation of top predators.Fil: Pia, Monica Valeria. Universidad Nacional de Córdoba. Facultad de Ciencias Agropecuarias. Departamento de Desarrollo Rural. Area de Estadística y Biometría; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Renison, Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Córdoba. Instituto de Investigaciones Biológicas y Tecnológicas; Argentina. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales. Centro de Ecología y Recursos Naturales Renovables; ArgentinaFil: Mangeaud, A.. Universidad Nacional de Córdoba. Facultad de Ciencias Agropecuarias. Departamento de Desarrollo Rural. Area de Estadística y Biometría; ArgentinaFil: de Angelo, Carlos Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Nordeste. Instituto de Biología Subtropical; ArgentinaFil: Haro, J. G.. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales; Argentin

Impact of natural control agents of the citrus leafminer Phyllocnistis citrella on lemon trees varies among seasons

Studies on insect natural enemies and their effects on host populations are of immense practical value in pest management. Predation and parasitism on a citrus pest, the leafminer Phyllocnistis citrella Stainton, were evaluated by sampling over 3 years in four locations within a world leading lemon producing area in Northwest Argentina. Both mortality factors showed seasonal trends consistent across locations, with predation exerting earlier and more sustained pressure than parasitism, which showed wider seasonal variations. The dominant parasitoids, native Cirrospilus neotropicus and introduced Ageniaspis citricola, showed different seasonal trends: C. neotropicus was dominant in spring whereas A. citricola superseded it in autumn and winter. Although parasitism rates were relatively low, the native C. neotropicus revealed favourable features as potential control agent, by showing density-dependence, parasitism rates comparable with those of the specific A. citricola during part of the cycle, and earlier synchronization with the host. The study provides highly relevant information for a sustainable management of this worldwide pest, for which biological control is considered the best long-term option.Fil: Goane, Lucía. Universidad Nacional de Tucumán. Facultad de Agronomía y Zootecnia; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Casmuz, A.. Gobierno de Tucumán. Ministerio de Desarrollo Productivo. Estación Experimental Agroindustrial Obispo Colombres; ArgentinaFil: Salas, H.. Gobierno de Tucumán. Ministerio de Desarrollo Productivo. Estación Experimental Agroindustrial Obispo Colombres; ArgentinaFil: Willink, E.. Gobierno de Tucumán. Ministerio de Desarrollo Productivo. Estación Experimental Agroindustrial Obispo Colombres; ArgentinaFil: Mangeaud, A.. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales; ArgentinaFil: Valladares, Graciela Rosa. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Córdoba. Instituto Multidisciplinario de Biología Vegetal (p); Argentin