Abstract The enigmatic genus Stenocrates Burmeister has 52 species that are widely distributed from Mexico to Argentina, but mainly in South America. In the present study, the larva of the third instar and pupa of Stenocrates agricola Dechambre & Hardy, 2004 are described and illustrated based on specimens from Argentina, this being the first description of immatures for the genus. The adult is also redescribed, significantly expanding the number of characters and providing information on the natural history of this species. In addition, 28 species of Cyclocephalini and 20 species of Pentodontini are morphologically compared, emphasizing the most useful larval characters used among these beetles. Stenocrates agricola shows frequent and common characters of Pentodontini species but scarce (and even absent) characters typical of Cyclocephalini species, including some considered diagnostic for this tribe. Accordingly we consider that the tribal position of Stenocrates remains controversial and more study is needed to clarify the tribal status of Stenocrates. We believe that larval morphology provides important information in systematics studies that can clarify tribal relationships within the Dynastinae.

Scarabaeinae assemblages composition from Colonia Benitez Reserve are assessed. Six samples using pitfalls, baited with squid and dung, and light traps, were carried out in dry and rainy seasons in 2 environments. A total of 3,369 specimens were caught belonging to 26 species. Eurysternus aeneus , Canthon quinquemaculatus , Canthon chalybaeus , Deltochilum komareki and Canthidium sp. represented 65% of all captures. Non-parametric richness estimators showed a reliable inventory. Significant differences in the Scarabaeinae assemblages structure was observed between periods, among baits and between sampled months, but not among environments. Abundance and diversity were slightly higher in the dry season. Richness, abundance and diversity were higher in the dryer period and in March (2011). More species were captured in excrement traps and more individuals in carrion traps. Maximum temperature was the variable that best explained the variation in the community structure. This is the first study of Scarabaeinae diversity in a protected area of the Ramsar Site Chaco Wetlands. The observed richness highlights the importance of maintaining even small areas for conservation purposes.

Se describe la composición de escarabeinos de la Reserva Natural Educativa Colonia Benítez. Se realizaron 6 muestreos en bosque de quebracho y selva en galería en periodo seco y lluvioso. Los escarabajos se recolectaron mediante trampas cebadas con materia fecal y calamar, y con trampas de luz. Se recolectaron 3,369 ejemplares de 26 especies. Eurysternus aeneus , Canthon quinquemaculatus , Canthon chalybaeus , Deltochilum komareki y Canthidium (Canthidium) sp., representaron el 65% del total de los individuos. Los estimadores no paramétricos de riqueza indican un porcentaje alto de completitud del inventario. La estructura del ensamble varió significativamente entre periodos, diferentes tipos de cebo y en los meses de muestreo, no así entre ambientes. En épocas secas, la abundancia y diversidad fueron mayores que en el periodo lluvioso. En marzo del 2011 se registró la mayor riqueza, diversidad y abundancia. Mediante trampas cebadas con materia fecal se obtuvo la mayor riqueza y con las de calamar la mayor abundancia. La temperatura máxima fue la variable que mejor explicó los cambios en la composición del ensamble. La riqueza observada demuestra que incluso pequeñas zonas boscosas son importantes áreas de conservación. Este es el primer estudio de la diversidad de Scarabaeinae en el Sitio Ramsar Humedales Chaco.