The annual life history of a population of the aquatic Coleopteran Derallus angustus (Coleoptera: Hydrophilidae)

ABSTRACT

Derallus Sharp, 1882 is a Neotropical genus of aquatic coleopterans that belongs in the tribe Berosini and includes 15 species. D. angustus Sharp is widely distributed from Guatemala to Argentina. The population dynamics of this species was studied by periodic sampling of a natural population from the southernmost Subtropical Domain of the Neotropical Region. The study site was near Punta Lara (34 degrees 47' S, 58 degrees 01' W; Ensenada, Buenos Aires province, Argentina). Twenty seven samples consisting of 20 units of aquatic vegetation (200 cm2 each) were taken during one year. Larvae and adults were removed from the vegetation and counted (pupae were not studied). There was a peak of first instar larvae abundance at the end of spring, and another at the end of summer. Adults and third instar larvae were present throughout the whole year. The population is interpreted as being univoltine and including two periods of enhanced reproductive activity.

RESUMEN

Derallus Sharp, 1882, de distribución Neotropical, pertenece a la tribu Berosini y está representado por 15 especies. D. angustus Sharp está ampliamente distribuida desde Guatemala hasta Argentina. El objetivo de este trabajo es el estudio de la dinámica poblacional de esta especie, en un limnótopo ubicado en el extremo sur del Dominio Subtropical de la Región Neotropical. l sitio de muestreo está localizado en Punta Lara (34°47’ S, 58°01’ W, Ensenada, Buenos Aires Province, Argentina). Se realizaron 27 muestreos durante un período de un año, cada uno consistió en la extracción de 20 muestras al azar de 200 cm² de vegetación flotante. El estado de pupa no fue incluido en este estudio. Se reconocieron dos picos de máxima abundancia del primer estadio larval (el primero a fines de primavera y el otro a fines del verano). Durante todo el período de estudio se registraron tanto adultos como larvas de tercer estadio. Se interpreta que la población es univoltina con dos períodos de actividad reproductiva.