Background:

The study of the morphometry in aquatic insects is very important to understand some ecological processes such as biomass gain, development time of the species and the dynamics of the cohorts. In Colombia, there are no studies on length-dry weight relations at the species level in Anacroneuria nymphs.

Goals:

The aim of this study was to analyze the morphological characteristic of Anacroneuria marta and A. caraca and to determine possible linear functions that explain the relations between some body dimensions (total length and head width) versus dry weight.

Methods:

Organisms were collected in areas of rapids and pools of the Gaira River (Sierra Nevada of Santa Marta, Colombia) between October 2014 and March 2015. Nymphs were identified to species level and taxonomic entities were confirmed by a discriminate analysis, using measurements of ten morphological variables. In some organisms dry weight was obtained, which was correlated with length measurements by simple linear regressions.

Results:

The species A. marta and A. caraca showed statistically significant morphological differences, which confirmed these taxa. The power model was the best adjusted to show the relations of the total length (TL) and the width of the head (WH) with the dry weight (p <0.01).

Conclusions:

The relationships between body dimensions and dry weight were highly significant, for A. marta the best adjust was with the WH and for A. caraca was with TL, with explanations of 86% and 95% of the variations in biomass, respectively. These equations will serve as a basis for studies of determination of biomass in Plecoptera nymphs.