| Summary: | <p>The aim of this study was to examine the species composition and the abundance of solitary wasps that nest in preexisting cavities in the Ilha Anchieta State Park, Brazil. Sampling was made during two years utilizing trap-nests. Of the 254 nests obtained, 142 nests were built by 14 species belonging to four genera and four families. In the remaining 112 nests all immatures were dead by unknown causes or had been parasitized by natural enemies. The occupation of trap-nests occurred almost throughout the study period and the wasps nested more frequently during the super-humid season. <em>Trypoxylon lactitarse</em>, <em>Pachodynerus nasidens</em>, <em>Trypoxylon</em> sp.2 aff. nitidum and<em> Podium denticulatum</em> were the most abundant species. The sex ratios of <em>T. lactitarse</em> and <em>Trypoxylon</em> sp.2 aff. <em>nitidum</em> were significantly male-biased, whereas those of <em>Trypoxylon</em> sp.5 aff. nitidum and <em>P. nasidens</em> were significantly female-biased. Sex ratios of<em> P. denticulatum</em> and <em>P. brevithorax</em> were not significantly different from 1:1. Natural enemies emerging from the nests were identified as belonging to the families Chrysididae, Ichneumonidae and Chalcididae (Hymenoptera), the genus<em> Melittobia</em> (Hymenoptera, Eulophidae), and the species <em>Amobia floridensis</em> (Townsend, 1892) (Diptera: Sarcophagidae). The number of cells with dead immatures from unknown factors was significantly higher than the number of cells parasitized by insects.</p>
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