Abstract

Summary: The life cycles and the nymphal feeding habits of two mayfly species, Andesiops peruvianus (Ulmer, 1920) (Baetidae) and Meridialaris spina Pescador & Peters, 1987 (Leptophlebiidae) from the Chanlelfu stream (north Chilean Patagonia), are studied from January to December 2020, using a Surber net. Andesiops peruvianus shows a univoltine life cycle, with long recruitment and emergence periods (lasting around eight months on average) and with overlapping on consecutive generations. Meridialaris spina shows a bivoltine life cycle, with emergences in spring-summer and autumn. So, the life history of A. peruvianus agrees with that recorded in other latitudes, while the life cycle of M. spina is studied for the first time, cataloguing it as bivoltine, similar to some congeneric species. Both A. peruvianus and M. spina behave mainly as gatherer-collectors, but the first one also behaves as scraper. Ontogenetic shifts in their food consumption were also detected for both species, but while A. peruvianus ingests significantly more coarse particulate organic matter and fungi when bigger, M. spina ingests significantly more particulate organic matter of both coarse and fine sizes when bigger; both species ingest less diatoms when bigger. In the Chanlelfu stream, both species coexist within the same habitat but differ in their life cycles, timing of emergence, and feeding strategies, including ontogenetic shifts in diet. The obtained data are discussed in comparison with those known in species of both genera. Studying their life cycles and feeding strategies provides key insights into population dynamics, trophic interactions, and their role as bioindicators for ecosystem monitoring and conservation. © 2025 Société entomologique de France.