Larval growth and development in the caddisfly Cheumatopsyche brevilineata under natural thermal regimes

Cheumatopsyche brevilineata (Iwata) is a filter‐feeding caddisfly without distinct or distinguishable cohorts. In a semi‐natural channel, we reared fourth and fifth instar larvae of C. brevilineata in individual cages with hourly recording of water temperature. We calculated the individual growth rate from the wet‐weight gain of each larva, and the development rate from the ratio of larvae that progressed to the next instar or pupal stage during each rearing experiment. We analyzed the linear regressions of growth (increase in size) and development (physiological and morphological progression toward maturity) rates against the statistical parameters of water temperatures during each rearing period, i.e. mean and given percentiles of water temperatures. We presumed that the most appropriate parameter of water temperature to explain larval growth and development would show a peak value of the determination coefficients (r²) in the linear regressions. There were highly significant regressions in the growth rates for fourth and fifth instar larvae and in development rates for fourth instar larvae against every statistical parameter of water temperature, but not in the development rates for fifth instar larvae. For the growth of fourth and fifth instar larvae, we could not specify the most appropriate parameters of water temperatures, because we observed no clear peaks in the determination coefficients. For the development of fourth instar larvae, this parameter could be the 65th percentile value, where the development zero temperature and effective degree‐days were 11.1°C and 56 degree‐days, respectively.