Taxonomic information regarding Gyrinidae is mostly based on adults, especially due to the difficulty in collecting immatures and assigning them to a particular species. Association between immatures and adults is sometimes difficult because closely related species can be found in the same habitat. To solve this problem a feasible technique is rearing under laboratory conditions. However, this method is challenging because larval survival rate is usually low, and emulation of natural conditions is difficult. Molecular techniques, especially the use of the COI gene, have been applied to identify species and to associate different life stages. However, in some species groups this marker has not been successful in distinguishing closely related species. The objectives of this study are to describe the egg and the first two instars of Gyretes nubilus Ochs, 1965 and the egg of G. minax Ochs, 1967 and to evaluate the utility of COI to associate immatures and adults. The association of these immature stages with adults was done either rearing adults under laboratory conditions or by using DNA sequence data (COI), corroborating the utility of this molecular marker to associate immature and adults in Gyretes. These immature stages are described, including chaetotaxic analysis of larvae for the first time for the genus Gyretes Brullé, 1835. The eggs are described based on scanning electron microscopy. The eggs are similar to those of other Gyrinidae genera in having a micropylar region in the anterior pole and a longitudinal fissure, and by the absence of an aeropyle, but they differ mainly in characters related to chorionic structure and reticulation. Larvae of Gyretes can be distinguished from those of the other Neotropical Gyrinidae genera by a combination of several characters, including the frontoclypeal seta FR3 short, presence of three conspicuous additional setae on lateral region of parietal (contiguous to stemmata), and posterior margin of lacinia smooth, with apex not indented.

A checklist of all known species of the water beetle family Gyrinidae (whirligig beetles) recorded from Brazil is assembled. This checklist is based on literature published prior to 2012. A total of 206 species and subspecies are cited for Brazil, distributed among three genera (Enhydrus Laporte, 1834, Gyrinus Geoffroy, 1762 and Gyretes Brullé, 1835). For each species we also include a complete account of its nomenclature including synonyms and historical combinations. The geographical distribution of each species both inside and outside of Brazil is provided.

In most species of Gyrinidae, the immature stages are unknown, especially due to the difficulty in collecting the juveniles and assigning them to a particular species. Molecular association is a feasible technique that may solve this problem. Recent studies have used DNA sequence data, specifically the gene cytochrome oxidase subunit I (COI), to associate immature and adult stages, thus enabling the description of the former. The objectives of this study were (1) to describe and illustrate the immature stages of Gyrinus (Neogyrinus) rozei Ochs, 1953 including morphometric, chaetotaxic and bionomic information, and (2) to assess the usefulness of the gene COI to associate immatures and adults of Gyrinus. The studied specimens were collected in Roraima state, northern Brazil. The association of immature and adult stages was done either by rearing adults under laboratory conditions or by using DNA sequence data (COI). Eggs were described based on scanning electron microscopy; they are distinguished mainly by several features of chorion, micropyle and reticulation. Larvae of G. (N.) rozei can be distinguished from those of other Neotropical Gyrinidae by a combination of several characters, including the stipes with five robust hook-like additional setae on the dorsointernal margin, and the lacinia roughly hook-shaped. The pupa is similar to that of G. argentinus Steinhel, 1869, except for the number of setae on the body. The first record of the parasitoid wasp Melanosmicra sp. (Hymenoptera: Chalcididae) on a Gyrinus species is also provided.

The genus Gyretes Brullé, 1835 has 181 species occurring in Brazil, most of them known in the country’s North Region. In this study, we record for the first time the occurrence of Gyretes minax Ochs, 1967 and Gyretes puberulus Ochs, 1967 in Maranhão state, northeastern Brazil. We also provide a diagnosis and illustrations for each of these species and comment on their geographical distributions.

In a recently published paper on the Gyrindae of Brazil (Colpani et al. 2014) a checklist of all known species from this country was given. This addition to the knowledge of Gyrinidae, based on literature published prior to 2012, comprises 206 species and subspecies and gives a complete account of the nomenclature for each taxon including synonyms and historical combinations. Additionally, the geographical distribution–both inside and outside of Brazil–of each species is provided. Although the authors have studied the literature (about 120 publications, most of them in French or German) very carefully, it was quite inevitable that some mistakes were made.