The Influence of Temperature and Food Quality on the Growth ofHydropsyche betteni(Trichoptera) andSimulium vittatum(Diptera)

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ABSTRACT Growth responses of Simulium vittatum and Hydropsyche betteni were observed at 5 C, 14 C and 20 C while on diets restricted to sterile or conditioned fine particulate leaf detritus (FPOM), cultured bacteria (Escherichia coli), a filamentous cyanobacterium (Oscillatoria lutea), two eukaryotic algae (Ulothrix confervicola and diatoms), and Daphnia magna (H. betteni only). Simulium showed little growth at 5 C regardless of food type; however, at 14 C growth of Simulium on conditioned leaf FPOM and O. lutea was greater than on sterile leaf FPOM or confervicola all of which resulted in lower growth rates than E. coli and diatoms. Growth was highest at 20 C, with all foods producing similar growth responses except sterile leaf FPOM, which produced a lower growth rate. Hydropsyche & betteni also grew little or not at all at 5 C but showed positive growth on all foods at 14 C; furthermore, at 14 C, growth on algae and Daphnia was higher than for detrital/bacterial or cyanobacterial foods. At 20 C growth was negative on detrital FPOM, E. coli and O. lutea but positive on diatoms and Daphnia. These data suggest that colder temperatures restricted growth of both test animals regardless of food quality. Also, H. betteni could not use detrital/bacterial foods as a sole source of energy (especially at temperatures ≥ 20 C) whereas Simulium grew equally well on algae, cyanobacteria and bacteria either alone or associated with detritus. Differences in growth responses to temperature and food type may help explain observed differences in distribution and abundance of these two species below lake outlets with epilimnial versus hypolimnial releases.