Effect of Permanent Shading on Adult Size and Biomass of the Caddisfly <Emphasis Type="Italic">Lype phaeopa</Emphasis> (Stephens, 1836) (Psychomyiidae)

To investigate the effect of shading on the development of aquatic insect larvae, estimated by the size and biomass of freshly emerged adults, a laboratory experiment was conducted in which larvae of the psychomyiid caddisfly Lype phaeopa were reared in glass aquaria covered by gauze pervious to light and compared to aquaria which were covered by a black textile distinctly reducing the light irradiation. Seven submerged branches colonized by larvae of L. phaeopa were collected from a small lowland stream, cut in two equally sized halves and one of the halves was reared under natural light and the other one under shaded condition. The hypothesis of the study was that larvae reared under natural light conditions can develop faster resulting in earlier emergence and larger adults compared to larvae reared under a shaded conditions. Females were always significantly larger and heavier than simultaneously emergent males (paired t-test, p < 0.001) independent of the treatment. The experiment revealed no effects of the shading on the adult size and biomass of emergent adults, neither for males (t-test, p = 0.197) nor for females (p = 0.303). Adult biomass was influenced by seasonal temperature (smaller adults during the warm summer months). Females’ biomass was also different between the branches independent from the treatment (one way ANOVA, p = 0.002) whereas males showed only a trend (p = 0.055). The shading displayed a significant effect on the emergence date of males with earlier emergence in the light treatment compared to the dark treatment (t-test, p = 0.046), but this could be not ascertained for females (p = 0.828). The experiment indicated that shading has no significant effect on the adult biomass of L.␣phaeopa, but it could delay the time of emergence in males. Main driving factors of larval development and subsequent adult biomass in L. phaeopa were temperature and habitat quality.