Leaf abundance and phenolic concentrations codetermine the selection of case-building materials by Phylloicus sp (Trichoptera, Calamoceratidae)

Phylloicus sp. larvae live on leaf patches in slow flowing waters and build dorso-ventrally flattened cases from leaf pieces. We hypothesized that Phylloicus larvae are selective towards certain leaf species to build a more resistant case. We exposed Phylloicus larvae to equal-area leaf discs of three plant species from the Brazilian Cerrado (Myrcia guyanensis, Miconia chartacea and Protium brasiliense) and one non-native species (Eucalyptus camaldulensis). Phylloicus larvae built cases with discs of all plant species. However, discs of E. camaldulensis and M. guyanensis were used more (36.4% and 35.7%, respectively) than those of P. brasiliense (20.0%). Discs of M. chartacea were used in an intermediate proportion (28.6%). Selection was resource density-dependent, i.e. when P. brasiliense was offered at higher abundance, it was used more frequently by larvae (ANOVA, P < 0.001). Plant species differed in leaf toughness, phenolic concentration and biomass:area ratio (Kruskal-Wallis, P < 0.05). Larvae preferentially used leaves with higher phenolic concentrations (R (s) = 0.907, P < 0.001) independently of toughness and biomass:area ratio. We suggest that Phylloicus selects for case-building leaves that are chemically protected against microbial degradation and shredder consumption, and this selection depends on leaf abundance. Our results also reinforce the importance of riparian resources and their diversity to the maintenance of aquatic consumers in tropical shaded streams.