The role of bacteria in the nutrition of aquatic detritivores.

Bacteriological analyses of the guts of four common lotic invertebrates are described. The results from these analyses suggest thatSimulium andChironomus digest at least half of the bacteria that they ingest in situ, but no evidence has been found for the digestion of bacteria byBaëtis or byEphemerella. Moreover,Simulium andChironomus do not appear to be selective, with regard to bacterial type, in their digestion. The limitations of the method are discussed and the relative importance of bacteria compared with other components of the insects' diet is assessed. Evidence is presented which supports the hypothesis that bacteria are not as quantitatively important as other components of the detrital food material.