Effect of current velocity and photoperiod on the behavior of Brachycentrus americanus.

Abstract

The effect of current velocity and photoperiod on the behavior of the Trichoptera, Brachycentrus americanus (Banks) was studied in artificial streams. Four streams, one stagnant, one with slow current, one with moderate current, and one with fast current, were used for observations over a twenty-four hour period. Three distinct and mutually exclusive behavior types, filter feeding (attached to substrate with hind legs fanned in current), withdrawn (motionless and retracted into the case), and active non-feeding behaviors (including crawling, drifting and aggressive interactions), were recorded every two hours over three separate twenty-four hour periods. In addition, the number of individuals joined together was recorded. The study was conducted under a controlled photoperiod of ten hours of light and ten hours of darkness separated by two hour twilight periods. Differences in behavior were only apparent between the stagnant stream and those with current; the velocity of current had little effect on behavior. There was little diel periodicity to the behaviors, with only active non-feeding behaviors more prevalent between 8 pm and 6 am. This pattern may have been a result of experimental design. The significance of the results was limited by the sample size and the small number of replicates.