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Abstract Studies of the relationships between the temporal variation of biological phenomena and environmental factors are essential to understanding the dynamics of communities. Phenology is a structuring element and, together with voltinism, is related to timing of reproductive activities. The aim of this study is to ascertain the structure and composition of the Chironomid assemblage and its emergence patterns in relation to the environmental variables through the use of the Chironomid pupal exuviae technique using the Neotropical streams as a model. The streams presented similar species compositions. The highest density of pupal exuviae was recorded during spring and the greatest richness in late summer and early autumn. Chironominae presented greater prevalence throughout the year with oscillations for Orthocladiinae and Tanypodinae. Chironominae and Tanypodinae presented emergence peaks in spring-summer and Orthocladiinae in autumn-winter. Rainfall, photoperiod and water and air temperatures structured the Chironomid assemblage, influencing emergence. Univoltine, bivoltine and multivoltine species were recorded. The species presented interspecific synchronization in emergence peaks at different times of the year.

The pupa of Tanytarsus alatus Paggi (1992) is described and figured for the first time. Notes for comparison with other species of the genus are provided, as well as brief notes on its geographic distribution.

The taxonomy of Chironomidae is strongly supported by the integration of morphological characteristics of all stages of the life cycle, which can be obtained through laboratory rearing. This study was developed in laboratory to test rearing method for lotic Chironomidae larvae. The method included constant water circulation and different food items. This methodology allowed obtaining associations of larva, pupa and adult stages for the identification of species from an Argentinean region in which the knowledge of Chironomidae family is incipient.