Substrate Attachment by Drifting Aquatic Insect Larvae

Abstract

A series of laboratory experiments was designed to evaluate sediment type and illumination as factors affecting substrate attachment by 3 species of drifting aquatic insect larvae. Stone or cobble sediment patches with (natural) or without (sterile) an epilithic food resource were placed in artificial stream channels. Larvae of Stenacron interpunctatum (Ephemeroptera), Acroneuria abnormis (Plecoptera), and Chimarra aterrima (Trichoptera) were drifted over these patches. Attachment was partitioned into (1) settling and (2) failure to return to the drift (delayed drift). Significant sediment effects on settling were observed with S. interpunctatum and C. aterrima, for the former only during daylight. For all 3 species, significantly fewer animals settled in darkness. Significant delayed drift occurred in both S. interpunctatum and C. aterimma, but only in darkness, off sterile sediments, for the former. These results suggest that invertebrate drift may function as a direct, one—way link between substrate specific faunal associations. A similar experiment tested the effect of a predator (A. abnormis) on substrate attachment by drifting prey (S. interpunctatum). No predator effect was observed on either settling or delayed drift of the prey. Repeating the first series of experiments with killed animals allowed an evaluation of the relative importance of behavior and morphology in substrate attachment. A sediment effect was observed only in A. abnormis, and no settling differences were observed between S. interpunctatum and C. aterrima, species of strikingly different morphology. Killed animals rarely reentered the drift after settling. For these species, settling and delayed drift were much more a function of behavior than of morphology.