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

RODRÍGUEZ J. S.; MOLINERI C.; DOS SANTOS D. A.

La Plata

Congreso; INTERNATIONAL CONGRESS OF ODONATOLOGY; 2015

Argia Rambur (Coenagrionidae) is a diverse genus found in the New World. They inhabit lotic or semilotic environments, but a few species occur in lentic habitats. Argia joergenseni breeds in streams across the Yungas Cloud Forest and other ecoregions from Argentina and Bolivia. In Tucumán it is the most frequent and abundant species of damselfly. The aim of this study was to investigate the life cycle and emergence pattern of A. joergenseni in one protected stream reach of this province. "Las Conchas" is a third-order stream flowing 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 to April 1996. Head capsule width in dorsal view, and body length (without caudal lamellae) were measured under a stereo microscope using an ocular micrometer. Six size-classes were defined to classify the 920 specimens collected, and the relative frequency of each class was studied through the sampling period. Mature larvae were present during most of the studied period, indicating a rather constant 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 low temperatures). Larger nymphs became dominant at the end of the winter and beginning of spring, coincidently with raising temperatures. More than one cohort developed simultaneously, a winter cohort reaching larger body sizes (emergency at size-class 6), and a summer cohort emerging at smaller size-classes (class 5 or even 4). Life cycle duration and its dependence on temperature are discussed.