Diversity of Auchenorrhyncha (Hemiptera: Cicadellidae: Delphacidae) Associated with Vicia villosa in Southern Buenos Aires Province, Argentina
Abstract
Among the Hemiptera, the Auchenorrhyncha are well known owing to their phytosanitary relevance since the group includes pathogen vector species able to damage commercial crops. Vicia villosa Roth (Fabaceae) is a fodder plant species, mainly distributed in central Argentina. Previous contributions have shown that V. villosa is colonized by diverse species of Auchenorrhyncha, either naturalized or native to valley of Colorado River area, in southern Buenos Aires province. To date, the only information about the species of hoppers associated with Vicia has come from preliminary field observations. The dearth of demographic knowledge about these phytophagous insects associated with this crop in Argentina motivates the study. The aims of this work were: 1) to characterize the diversity of the species of Auchenorrhyncha associated with V. villosa and 2) to determine the seasonal fluctuation of the most abundant species in relation to local weather variables and crop phenological phases. The study was conducted in Vicia plots located at EEA INTA Hilario Ascasubi (S 39° 23' 36" -W 62° 37' 59", 15 m.a.s.l.) southern Buenos Aires province. The specimens were collected with a sweep net during 2 yr (2009 and 2011). Weather variables were recorded using a meteorological station located at the sampling site. To measure species richness and community diversity we calculated both Margalef (DMg) and the Simpson (D) indexes, and also, the Relative Importance Index (RII). The relationships between population densities of the leafhoppers, Paratanus exitiosus (Beamer) and Agalliana ensigera Oman (Cicadellidae), with weather variables were analyzed through simple and multiple linear regression. A total of 17 species were associated with V. villosa crops in Argentina, of which 15 belong to the Cicadellidae and 2 to the Delphacidae. Abundance and species richness were higher in 2009 than in 2011. In general, the results of the Margalef index showed that species richness was higher in 2009, while Simpson Index (D) indicated a higher dominance in 2011 than in 2009. The species, P. exitiosus and A. ensigera, stood out for their abundance, frequency and phytosanitary relevance during the sampling period. Both species presented population increases since Nov coinciding with different phenological phases of the crop and the maximum density of the canopy. Additionally, the population density of P. exitiosus showed strong dependence on the hydric balance and photoperiod, while A. ensigera was influenced by Degree-days10 and hydric balance . Vicia villlosa was a new host-plant record for 15 species. Buenos Aires province was cited as a new distribution record for 2 species.
Los hemipteros auquenorrincos son insectos de reconocida importancia fitosanitaria dado que reunen especies vectoras de patogenos que ocasionan danos a cultivos de interes comercial. Vicia villosa Roth es una especie forrajera, distribuida fundamentalmente en la region central de Argentina. Observaciones preliminares evidenciaron que V. villosa es colonizada por una diversidad de auquenorrincos, establecidos o nativos, en el area de riego del valle del Rio Colorado en el sur de la provincia de Buenos Aires. La falta de estudios poblacionales referidos a estos fitofagos asociados a dicho cultivo motivaron el planteo de los siguientes objetivos: 1) conocer la diversidad de las especies de auquenorrincos presentes a lo largo del ciclo de V. villosa y 2) estudiar la influencia de diversas variables climaticas locales sobre las poblaciones de las especies mas abundantes y asociar la presencia de estas a las fases fenologicas del cultivo. Los muestreos fueron realizados en lotes de vicia ubicados en la Estacion Experimental Agropecuaria (EEA) INTA Hilario Ascasubi (62° 37' 59" LO, 39° 23' 36" LS 15 msnm), al sur de la provincia de Buenos Aires. Los especimenes fueron colectados con red entomologica de arrastre durante dos anos (2009 y 2011). Las variables climaticas se registraron con una estacion meteorologica instalada en el sitio de estudio. Para el calculo de la riqueza especifica y la diversidad se utilizaron los indices de Margalef (DMg) y Simpson (D). Tambien se calculo el Indice de Importancia Relativa (IIR). La relacion entre la densidad poblacional de los cicadelidos, Paratanus exitiosus (Beamer) y Agalliana ensigera Oman con las variables climaticas fue analizada mediante regresion lineal simple y multiple. La abundancia y la riqueza especifica fueron mayores en 2009. En general, los valores de Margalef (DMg) denotaron una mayor riqueza especifica en 2009, mientras que el Indice de Simpson (D) mostro una mayor dominancia en el ano 2011. En ambos anos, las especies P. exitiosus y A. ensigera sobresalieron por su abundancia, frecuencia e importancia fitosanitaria. Las dos especies presentaron picos poblacionales desde noviembre en diferentes fases fenologicas del cultivo y cuando la canopea era ya muy densa. Sobre la base de los resultados obtenidos, la densidad de la poblacion de P. exitiosus en el cultivo de vicia mostro una fuerte dependencia con el balance hidrico y el fotoperiodo; mientras que A. ensigera estuvo influenciada por los grados dia10 y el balance hidrico. Vicia villlosa se registra como nuevo hospedante para 15 especies, de las cuales dos se citan por primera vez para la provincia de Buenos Aires.
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