Resumo. The objective of this study was to assess if larvae of Phylloicus spp. show any preference for leaves with or without microorganisms when building cases. Two experiments were realized at municipality of Presidente Figueiredo (Amazonas – Brazil), containing leaves treated with Hydrogen peroxide (H2O2), a compost that has an antimicrobial action, and another one with untreated leaves. In the first were observed the case-building by larvae of Phylloicus spp. and in the second was tested the preference by treated or untreated leaves. The larvae were monitored during 24 hours and to statistical analysis was used the t-test. Were not observed significant differences in the number of discs used by the larvae in the first experiment (p=0.24; t=-0.73) and no preference by type of leaf in the second experiment (p=0.41; t=0.23). Therefore, we do not recommend the use of hydrogen peroxide in studies that aim to eliminate microorganisms from decomposing leaves.