Length-mass relationships and seasonal dynamics of Apatania crymophila McLachlan, 1880 (Trichoptera: Apataniidae) caddisfly larvae associated with water moss in the middle reaches of the Yenisei River (Siberia)

Apatania crymophila McLachlan, 1880 is the most abundant species among trichopterans of the Yenisei River. The density of its free-moving larvae associated with water moss in the Yenisei River downstream of the high-pressure Krasnoyarsk Hydroelectric Plant dam was studied from June through November 2022. The biomass of A. crymophila larvae best correlated with case length, and the correlation was well fitted by linear equation; case length was also used to distinguish instars in this study. The abundance and biomass of A. crymophila larvae on water moss increased most rapidly (0.12 and 0.18 day-1, respectively) from early July to early August, when water temperature approached its seasonal maximum. The maximum value of the larval density on water moss was reached in October (1084 larvae per kg of fresh moss). The relationship between larval growth and water temperature suggests that altered environmental conditions in the Yenisei River downstream of the HEP can be considered as a factor favoring the abundancy of A. crymophila.