Effects of food quality on the growth of three Hydropsyche species (Trichoptera: Hydropsychidae)

Growth responses of third, fourth, and fifth instars of Hydropsyche betteni, H. slossonae, and H. sparna were observed while on diets restricted to leaf or fecal detritus, diatoms, or animal material. Larval weight increases were 7.0 times higher on an animal material diet and 4.6 times higher on a diatom diet than on either a leaf or fecal detritus diet. The relative percent contribution of each food type to larval growth in the field suggested detritus was of little importance to later instars; however earlier instars may depend more on detritus. Diatoms showed the greatest contribution to larval growth for all species and instars. Animal material varied in importance depending on season, species, and instar. These results suggest autotrophy may be a very significant factor in energy flow within stream ecosystems, especially in terms of filter-feeder diversity and abundance. No instar appeared to be better able to utilize one type of food over another. However, H. sparna larvae consistently grew faster than other species on all food types; its widespread distribution may be related to its ability to more efficiently utilize a variety of food resources.