Life cycle and emergence pattern of Argia joergenseni Ris 1913 (Coenagrionidae, Zygoptera) in a stream from Yungas mountain forest (Tucumán, Argentina)

JOSÉ S. RODRÍGUEZ, CARLOS MOLINERI & DANIEL DOS SANTOS

La Plata

Congreso; INTERNATIONAL CONGRESS OF ODONATOLOGY; 2015

Argia Rambur (Coenagrionidae) is a diverse genus found in the New World. They inhabit loticor semilotic environments, but a few species occur in lentic habitats. Argia joergenseni breeds in streamsacross the Yungas Cloud Forest and other ecoregions from Argentina and Bolivia. In Tucumán it is themost frequent and abundant species of damsely. The aim of this study was to investigate the life cycleand emergence pattern of A. joergenseni in one protected stream reach of this province. "Las Conchas"is a third-order stream owing through a Biological Reserve and is surrounded by Yungas forest.Larvae were collected weekly using a Surber sampler (0.09 m², pore size 1 mm) from April 1994 toApril 1996. Head capsule width in dorsal view, and body length (without caudal lamellae) weremeasured under a stereo microscope using an ocular micrometer. Six size-classes were defined toclassify the 920 specimens collected, and the relative frequency of each class was studied through thesampling period. Mature larvae were present during most of the studied period, indicating a ratherconstant emergence of adults that was corroborated with observations in the field. Immature larvae(size-classes 1 and 2) were dominant from March (end of the rainy period) to August (end of winter lowtemperatures). Larger nymphs became dominant at the end of the winter and beginning of spring,coincidently with raising temperatures. More than one cohort developed simultaneously, awintercohort reaching larger body sizes (emergency at size-class 6), and a summer cohort emerging atsmaller size-classes (class 5 or even 4). Life cycle duration and its dependence on temperature isdiscussed.