The insect group is one of the most diverse on the planet and due to habitat degradation, many of these species are becoming extinct, leaving a lack of information on the basic biology of each one. In this study, previously unseen information about nesting biology is revealed in Auplopus subaurarius trap nests. This is a solitary ectoparasitoid spider wasp that nests in preexisting cavities. We used a trap-nesting methodology to sample A. subaurarius in two different sampling periods (2017/2018 and 2020/2021) in three types of environment (forest, grassland and Eucalyptus plantation). In our study, the A. subaurarius nest building was more frequent during the hottest months of the year (November to March), with its highest abundance found within natural forest areas and in Eucalyptus plantation than in grassland areas. In addition, the species had two development times: a short one (three months) and a delayed one (up to one year). Moreover, females were larger than males (weight and size) and the species’ sex ratio had a tendency toward female production. Auplopus subaurarius presented seven natural enemy species: Ceyxia longispina, Caenochrysis crotonis, Photochryptus sp.1, Photochryptus sp.2, Messatoporus sp., Ephuta icema and Sphaeropthalma sp. We emphasize the importance of wooded environments to maintain the A. subaurarius populations and their associated interactors, both spiders and natural enemies, as these environments can provide better life conditions than grassland areas. Furthermore, other solitary wasps that may have the same lifestyle of A. subaurarius can also be improved by natural forest conservation and by good silviculture plantation planning, which should consider ecological aspects of Atlantic Forest landscapes.

Zethus is the largest vespid genus and, despite being very diverse in the Neotropical region, little is known about its biology and many species are known from only one sex. Zethini are centered in one of the controversies involving Vespidae phylogeny; increased knowledge of terminals will allow for more precise analyses, because some phylogenetically informative characters are observed in only one sex and others can be extracted from nests. With this in mind, complementary knowledge on Zethus pilosus is presented: the description of the female, of the male genitalia, of the nest and notes in its biology. Additional key features in the pronotum for identification of this species are provided. Nests were founded between December and April, presenting construction of partitions out of a combination of mud, sand, vegetable matter and insect parts. Development from egg to adult lasted an average of 39 days.

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Although diverse and widespread, there is much to improve on the knowledge of Zethus Fabricius, 1804 wasps. This includes aspects of many areas, such as data on taxonomy, behavior and biology. In the present study, we investigated Zethus plaumanni Bohart & Stange, 1965, a species hitherto known only from the female type in the literature, and worked to fill gaps on the knowledge of this species by describing the male and its genitalia, the nest structure and giving notes on the biology of individuals collected in trap-nests in southern Brazil. The male is diagnosable by characters also used for female identification. The nest follows the pattern of typical pre-existing cavity users, with a remarkable multi-layered nest plug. Sex ratio follows the 1:1 rule and sampling indicates diapause in the adult phase.