REANALYSIS OF FILTER-FEEDING BEHAVIOR OF CADDIS FLY (BRACHYCENTRUS) LARVAE REVEALS MASKING AND CIRCADIAN RHYTHMICITY

Data published on the subjectively determined presence or absence of c ircadian periodicity in feeding of Brachycentrus occidentalis Banks, a n aquatic insect belonging to the order Trichoptera, were reanalyzed b y statistical methods based on the cosine model. The 4h data far 5 day s of synchronized environmental conditions followed by 5 days of const ant conditions (using original values and purified values after remova l of an 8h component attributed to the feeding schedule) were quantifi ed for rhythm characteristics by the least-squares fit of cosines. A c ircadian rhythm was highly significant during synchronized conditions (light-dark and cycling water temperature) and in continuous light whe n water temperature continued to cycle. A circadian rhythm in the perc entage of larvae feeding during continuous light and constant water te mperature, which had not been observed by visual inspection in the ori ginal data, was detected in the unmasked data with a ''free-running'' period not overlapping 24.0h (95% confidence limits from 18.95h to 21. 66h). Effects of masking brought about by manually feeding the larvae every sh were statistically significant under both synchronized and co nstant environmental conditions.