Neotropical Research Articles

Notes on the genus Elegansovella Hirschmann, 1989 (Acari, Mesostigmata, Urodinychidae)

The genus Elegansovella Hirschmann, 1989 (Mesostigmata: Uropodina: Urodinychidae) is resurrected for species of the Uroobovella elegans-group. This genus differs from the other taxa of Uroobovella Berlese, 1903 sensu lato based on the shape of the idiosoma and the caudal and dorsal setae. Three species from the Uroobovella elegans-group are transferred to the genus Elegansovella, as E. pectintata (Hirschmann, 1973), comb. nov., E. pectinatasimilis (Hiramatsu, 1980), comb. nov. and E. serangensis (Hiramatsu, 1980), comb. nov. The other seven species from this species group are transferred to Monstrobovellagen. nov., as M. crustosa (Vitzthum, 1926), comb. nov., M. enodis (Hiramatsu, 1985), comb. nov., M. faceta (Hiramatsu & Hirschmann, 1978), comb. nov., M. facetaoides (Hiramatsu & Hirschmann, 1978), comb. nov., M. imadatei (Hiramatsu, 1980), comb. nov., M. incerta (Hiramatsu & Hirschmann, 1978), comb. nov. and M. incertaoides (Hiramatsu & Hirschmann, 1978), comb. nov. The new genus differs from Elegansovella by the shape of the idiosoma and the shape of marginal and dorsal setae. Six Monstrobovella species occur in the Oriental Realm and only one species is known from the Neotropical region. The present paper contains the description of a second Neotropical species of Monstrobovella (M. mancocapacisp. nov.) which was found in Peru. The new species differs from its Neotropical congener in the dorsal and marginal setation.

Diet overlap of overwintering migratory birds on the northern coast of the Yucatan Peninsula

Previous studies of overwintering migratory birds in neotropical environments have found that species co-occur in the same habitats despite high diet overlap. Hence, discovering subtle diet differences within habitats can help explain patterns in bird species diversity. The Yucatan Peninsula in Mexico is an important region for overwintering migratory birds, but little is known about how habitat differences in food resources contribute to bird diversity. To address the knowledge gap, we compared the degree of overlap in the diet of all terrestrial migratory birds within and between mangrove and tropical dry forests on the Yucatan Peninsula’s northern coast. We collected data on the consumption of food items through direct observation of birds feeding on four transects in each habitat every week (12 weeks) during the non-breeding season (i.e., overwinter, December-February). We recorded 19 species, 15 species in mangrove and 15 species in forest, with 11 of those found in both habitats. In both habitats, diet overlap was high. However, species present only in the tropical dry forest had less overlap than species occurring in both habitats, indicating that diet specialization might restrict the range of habitats that a species can occupy. On the other hand, species present only in the mangrove had similar diet overlap to species present in both habitats. The diet variation that did exist was greater within than between habitats possibly due to intraspecific diet differences among different geographic locations. Although small, within-habitat diet differences might be key to allowing species to coexist locally in the Yucatan, thus supporting studies demonstrating a similar mechanism in other neotropical regions. More generally, the information we provide on bird diet can be used to discover whether threats like anthropogenic development precipitate species loss via altering the resource base upon which birds rely.

Complete phylogeny of Micrathena spiders suggests multiple dispersal events among Neotropical rainforests, islands and landmasses, and indicates that Andean orogeny promotes speciation.

The Neotropical region is the most diverse on the planet, largely owing to its mosaic of tropical rainforests. Multiple tectonic and climatic processes have been hypothesized to contribute to generating this diversity, including Andean orogeny, the closure of the Isthmus of Panama, the GAARlandia land bridge and historical connections among currently isolated forests. Micrathena spiders are diverse and widespread in the region, and thus a complete phylogeny of this genus allows the testing of hypotheses at multiple scales. We estimated a complete, dated phylogeny using morphological data for 117 Micrathena species and molecular data of up to five genes for a subset of 79 species. Employing event-based approaches and biogeographic stochastic mapping while considering phylogenetic uncertainty, we estimated ancestral distributions, the timing and direction of dispersal events and diversification rates among areas. The phylogeny is generally robust, with uncertainty in the position of some of the species lacking sequences. Micrathena started diversifying around 25 Ma. Andean cloud forests show the highest in-situ speciation, while the Amazon is the major dispersal source for adjacent areas. The Dry Diagonal generated few species and is a sink of diversity. Species exchange between Central and South America involved approximately 23 dispersal events and started ~20 Ma, which is consistent with a Miocene age for the Isthmus of Panama closure. We inferred four dispersal events from Central America to the Antilles in the last 20 Myr, indicating the spiders did not reach the islands through the GAARlandia land bridge. We identified important species exchange routes among the Amazon, Andean cloud forests and Atlantic forests during the Plio-Pleistocene. Sampling all species of the genus was fundamental to the conclusions above, especially in identifying the Andean forests as the area that generated the majority of species. This highlights the importance of complete taxonomic sampling in biogeographic studies.

Pathogens associated with ticks (Acari: Ixodidae) and mammals in the Orinoquia region of Colombia: An approach to understanding vector-pathogen-host interactions

The hard tick clade (Ixodidae) currently comprises 762 species worldwide (266 Prostriata and 496 Metastriata). A quarter of hard ticks are found in the Neotropical region, and 42 species have been documented in Colombia. Ixodidae species are important vectors of pathogens such as bacteria, helminths, protozoa, and viruses. In tick-borne diseases, vertebrate hosts perform an important role in the transmission, maintenance, and spread of pathogens. Colombia ranks sixth among countries with the highest mammal biodiversity, with a total of 548 species, where some of these species may be involved in pathogen transmission cycles with ticks as vectors. This research evaluated the presence of two genera of bacteria (Borrelia and Rickettsia) and the protozoan (Babesia) in ticks and mammals in the Orinoquia region of Colombia, establishing interaction networks. The information comes from 734 mammals (655 wild and 79 domestic), belonging to 59 species. Tick infestation (n = 1,805) was found with 14.85 % (n = 109) of the examined mammals and corresponds to nine tick species confirmed morphologically and molecularly. To detect pathogens 272 ticks were collected while feeding on 96 mammals; samples from 93 mammals were analyzed. The presence of borreliae from the relapsing fever group (RFG) and the Lyme disease group (LDG) were detected. Rickettsia spp. was detected in ticks and mammals, while Babesia bigemina was only detected in ticks. This research is the first to address the prevalence of zoonotic pathogens in domestic and wild mammals infested with hard ticks in the Department of Arauca, Colombia. Considering that reporting cases of infections with Babesia, Borrelia, and Rickettsia in Colombia is not mandatory, their impact on public health cannot be estimated. This highlights the importance of continuously detecting, confirming, and identifying these and other important pathogens within the "One Health" framework, as they have a significant economic and medical-veterinary impact globally.

Phylogenomics of the catfish family Pimelodidae with focus on the genus Pimelodus support the recognition of Sorubiminae and Pimelodinae (Teleostei, Siluriformes)

AbstractPimelodidae is a family of large‐sized catfishes consisting of 116 valid species divided into 30 genera distributed in the Neotropical region. Despite recent advancements in understanding the pimelodid phylogeny, several internal relationships have remained unclear and have received limited support from various phylogenetic analyses. We provide a new genomic dataset comprising 55 species representing 25 genera of Pimelodidae and related siluriform families Aspredinidae, Auchenipteridae, Cetopsidae, Doradidae, Diplomystidae, Heptapteridae, Loricariidae, and Pseudopimelodidae. Our phylogenetic analyses support the monophyly of Pimelodidae, as well as the existence of four major lineages: the Steindachneridion clade, the Leiarius + Phractocephalus clade, and two major subclades herein classified as Sorubiminae and Pimelodinae. Our topology resolves Phractocephalus sister to Leiarius differing from previous phylogenies. In Sorubiminae, Zungaro is sister to two large clades: one with Sorubim, Sorubimichthys, and Pseudoplatystoma, and the other with Hemisorubim, Platysilurus, Platystomatichthys, Brachyplatystoma, and Hypophthalmus. In Pimelodinae, we found the Pimelodus ornatus clade, the calophysines, and the clade with Exallodontus, Propimelodus, and Pimelodus altissimus closer to the Pimelodus group. Parapimelodus, Duopalatinus, Iheringichthys, and Bergiaria are included within the Pimelodus group. The Pimelodus group contains four main components: (1) Duopalatinus peruanus, (2) the trans‐Andean Pimelodus grosskopfii; (3) Pimelodus maculatus clade with species from the Brazilian Shield in southeastern Brazil; and (4) Pimelodus blochii clade composed by species from the Amazon, Orinoco, Paraná‐Paraguay, Parnaíba, São Francisco and coastal drainages of the Guiana Shield. The P. maculatus clade is composed by phenotypically diverse species, and the P. blochii clade houses species morphologically similar that appear nested within the widely distributed P. blochii.

New records of helminth infections in Bothrops atrox Linnaeus, 1758 from Marajó Island-Brazil and a literature review with a check list of helminths infecting Bothrops species (Squamata, Viperidae) in the neotropical region

Snakes of the genus Bothrops inhabit tropical forests in Central and South America and are important for the biomedical and pharmaceutical industries because of the chemical properties of their venom. They serve as either definitive or intermediate hosts for many parasitic helminths. The Marajó Island (Brazil) is the natural habitat of venomous snakes, Bothrops atrox and Bothrops marajoensis, which are often found around rural and peri-urban areas and are known to bite humans. Samples of helminths parasitizing the oral cavity, subcutaneous tissues, coelomic cavity, and intestine of four B. atrox from Marajó Island (Pará-Brazil) were collected. The specimens studied were taxonomically classified as trematodes of the species Stycholecitha serpentis, nematodes of the genera Eustrongylides and Camallanus and cystacanths of an acanthocephalan of the genus Centrorhynchus. The aims of the present study were: to record helminths found in B. atrox from the Marajó Island; to discuss their role as definitive, intermediate, or paratenic hosts; and to compile a list of helminths that have been recorded in snakes of the genus Bothrops of the Neotropical region.

Endemism and regionalization of Neotropical mammals: a multi-taxon analysis

Abstract The distribution pattern of a taxon is a consequence of historical and contemporary processes—specifically ecological and evolutionary processes—which tend to result in distributional congruence among species that respond similarly to the same processes. This congruence leads to the establishment of areas of endemism that are important for delimiting biogeographic regions. In the Neotropical region, different definitions of area of endemism have been proposed based on the distributional patterns of mammal species, each according to different methods and assumptions. In this study, we aimed to identify areas of endemism of Neotropical mammals, represented by 361 species of Placentalia (Xenarthra, Chiroptera, and Carnivora) and Marsupialia (Didelphimorphia and Paucituberculata), using an endemicity analysis implemented by the software NDM (eNDeMism software) and a hierarchical cluster analysis based on Simpson’s beta dissimilarity metric (βsim). The results suggest alternative spatial configurations within northern and southern parts of the Neotropics along transition zones. Additionally, there are indications of more restricted areas of endemism throughout the Neotropical region and with more species supporting the areas, such 1 area located in the region corresponding to the Atlantic forest and 2 areas corresponding to Mexican transition zone. The study enhances our understanding of Neotropical mammal biogeography and underscores the importance of using primary distribution data. Previous studies found 82 endemic species based on range maps, whereas our analyses identified 172 endemic species, including 125 that are newly proposed as such, and also confirmed the existence of 47 previously reported endemic species.

Morphological and molecular data on helminths of Didelphis virginiana and Philander vossi (Mammalia: Didelphidae) from the Yucatán Peninsula, southeast Mexico

In the present study, helminths from six Didelphis virginiana and one Philander vossi are reported using morphological techniques (clearing, staining, and scanning electron microscopy). Additionally, the 28S rRNA sequences of individuals from nine helminth taxa are provided. Phylogenetic analyses were performed with the new 28S rRNA sequences to confirm the identification and the genealogical relationships of the parasites. Thirteen helminth taxa were identified, comprising the trematodes Brachylaima sp. and Platynosomum illiciens, the cestode Mathevotaenia sp., the nematodes Cruzia americana, Cruzia tentaculata, Viannaia arriaguensis, Viannaia sp., Travassostrongylus sp., Strongyloides sp., Turgida turgida, Trichuris minuta, and Trichuris sp., and the acanthocephalan Oligacanthorhynchus microcephalus. All opossums were infected with at least four helminth taxa. In total, 17 new 28S rRNA sequences from nine helminth taxa were provided. These data, combined with previous records in Mexico, increase the number of helminth taxa parasitizing D. virginiana and P. vossi to 41 and 29, respectively. However, these reports are incompletes and concentered in localities of some states. It is possible that new surveys in the Nearctic and even Neotropical regions will reveal a higher helminth diversity in these mammals in the country.

Geminiviridae and Alphasatellitidae Diversity Revealed by Metagenomic Analysis of Susceptible and Tolerant Tomato Cultivars across Distinct Brazilian Biomes.

The diversity of Geminiviridae and Alphasatellitidae species in tomatoes was assessed via high-throughput sequencing of 154 symptomatic foliar samples collected from 2002 to 2017 across seven Brazilian biomes. The first pool (BP1) comprised 73 samples from the North (13), Northeast (36), and South (24) regions. Sixteen begomoviruses and one Topilevirus were detected in BP1. Four begomovirus-like contigs were identified as putative novel species (NS). NS#1 was reported in the semi-arid (Northeast) region and NS#2 and NS#4 in mild subtropical climates (South region), whereas NS#3 was detected in the warm and humid (North) region. The second pool (BP2) comprised 81 samples from Southeast (39) and Central-West (42) regions. Fourteen viruses and subviral agents were detected in BP2, including two topileviruses, a putative novel begomovirus (NS#5), and two alphasatellites occurring in continental highland areas. The five putative novel begomoviruses displayed strict endemic distributions. Conversely, tomato mottle leaf curl virus (a monopartite species) displayed the most widespread distribution occurring across the seven sampled biomes. The overall diversity and frequency of mixed infections were higher in susceptible (16 viruses + alphasatellites) in comparison to tolerant (carrying the Ty-1 or Ty-3 introgressions) samples, which displayed 9 viruses. This complex panorama reinforces the notion that the tomato-associated Geminiviridae diversity is yet underestimated in Neotropical regions.

Some bats are here: Reducing the Wallacean shortfall of bats in the amazon.

The Amazon rainforest has approximately 23% of its sampled area dedicated to bats, making it one of the least sampled and most diverse regions for bats in Brazil. The lack of sampling results in a lack of knowledge regarding the accurate geographical distribution of bat species. This lack is referred to as the Wallacean shortfall, which should be addressed with primary data obtained from insitu collections. However, the use of Species Distribution Models (SDMs) can help alleviate this gap. The states of Pará and Acre are located in the Brazilian Amazon. So, our objective is to decrease the Wallacean shortfall concerning Amazonian bat species. To achieve this, we provide (i) a list of bat species sampled in the states of Pará and Acre in the last 5 years (2017 to 2022); (ii) the potential distribution of species considered as new occurrences for the region; and (iii) the potential distribution of species classified as Data Deficient (DD) and Near Threatened (NT) according to the IUCN classification. With 96 nights of collection and 129,600 m2h of mist netting, we obtained 75 bat species, with an estimated total of 94.78 species. Additionally, 21 species were considered as range extensions. The Brazilian Amazon region has a vast geographic expanse and few established research centers, resulting in a limited sampling of bats and other biological groups. Furthermore, we draw attention to the significant number of bat species with expanded geographical distributions, with 21 out of the 75 sampled species. This should be a reminder that primary biogeographic data is still necessary for the neotropical region.

New distributional records for Khamul Gates, 2008 (Hymenoptera: Eurytomidae) from Brazil

Khamul Gates, 2008 (Hymenoptera: Eurytomidae), a small genus poorly represented in entomological collections, is widely distributed in the Neotropical region, occurring mainly in tropical forests. This study reports the expansion of the geographic distribution of Khamul erwini Gates, 2008 to the state of Amazonas and Khamul lanceolatus Gates, 2008 to the states of Goiás and Minas Gerais, Brazil. These new records are an important contribution to understanding the distribution patterns of Khamul species in Brazil. In addition, illustrations and maps of geographic distribution of the studied species are provided based on new records and data from the literature.

A comparative analysis reveals the genomic diversity among 8 Muscovy duck populations.

The Muscovy duck (Cairina moschata) is a waterfowl indigenous to the neotropical regions of Central and South America. It has low demand for concentrated feed and strong adaptability to different rearing conditions. After introduced to China through Eurasian commercial trade, Muscovy ducks have a domestication history of around 300 years in the Fujian Province of China. In the 1990s, the commodity Muscovy duck breed "Crimo," cultivated in Europe, entered the Chinese market for consumption and breeding purposes. Due to the different selective breeding processes, Muscovy ducks have various populational traits and lack transparency of their genetic background. To remove this burden in the Muscovy duck breeding process, we analyzed genomic data from 8 populations totaling 83 individuals. We identify 11.24 million single nucleotide polymorphisms (SNPs) and categorized these individuals into the Fujian-bred and the Crimo populations according to phylogenetic analyses. We then delved deeper into their evolutionary relationships through assessing population structure, calculating fixation index (FST) values, and measuring genetic distances. Our exploration of runs of homozygosity (ROHs) and homozygous-by-descent (HBD) uncovered genomic regions enriched for genes implicated in fatty acid metabolism, development, and immunity pathways. Selective sweep analyses further indicated strong selective pressures exerted on genes including TECR, STAT2, and TRAF5. These findings provide insights into genetic variations of Muscovy ducks, thus offering valuable information regarding genetic diversity, population conservation, and genome associated with the breeding of Muscovy ducks.

Revision of the genus Eugenys Quate, 1996 (Diptera: Psychodidae), with the description of three new species

We review the diagnosis of the genus Eugenys Quate, 1996 (Diptera: Psychodidae) which occurs in the Neotropical Region. Initially known from Costa Rica, Nicaragua, and Panama, we describe one additional species from Costa Rica, Eugenys singularis sp. nov., and two species from Ecuador, namely, Eugenys micra sp. nov. and E. upsilon sp. nov., bringing the total known species to six. This study provides detailed descriptions of the new species based on male and female specimens, along with the first DNA barcodes for the genus and some of the newly described species. We also provide an identification key for identifying male specimens of the genus worldwide. Finally, we discuss the morphological characteristics of Eugenys and compare the genus with other taxa, tentatively suggesting a placement within the tribe Pericomaini.

Biologia de nidificação de Euglossa cordata (Apidae: Euglossini) em áreas abertas no Extremo Sul Baiano

The genus Euglossa comprises a group of approximately 110 cataloged bee species found throughout the Neotropical region. Among these species, Euglossa cordata (Linnaeus, 1758) has a wide distribution in different environments. This research aimed to analyze aspects of the nesting biology of E. cordata in open areas near Atlantic Forest fragments in the Extreme South of Bahia, Brazil. Collections were carried out using PET bottle traps, a methodology commonly employed for capturing Meliponini but adapted for the first time in this study, presenting a low cost and good applicability for studies on Euglossa bees. Ten traps were randomly distributed in open environments at the Federal Institute of Bahia. Three nests of E. cordata were found, with a total of thirteen brood cells and six female emergences in traps 2 and 3. In all nests, the cells were constructed in a circular manner and arranged close to each other. The cells were built with resin and had a scalene trapezoid shape with variations in diameter and length. Studies on bees of the Euglossini tribe, popularly known as orchid bees, often focus on males collected using odor baits. Conversely, studies on females and nesting biology are scarce. Thus, methodologies that facilitate the capture of females and Euglossini nests are extremely relevant for enhancing our understanding of the group.

Potential distribution of wild edible fruit trees under climate change scenarios: promoting food security in a Neotropical region

Potential distribution of wild edible fruit trees under climate change scenarios: promoting food security in a Neotropical region

Belostomatidae Leach, 1815 (Insecta: Hemiptera: Heteroptera: Nepomorpha) of northeastern Brazil

Belostomatidae Leach, 1815 (Insecta: Hemiptera: Heteroptera: Nepomorpha), also known as giant water bugs, is a family with 11 genera and about 160 described species, most of which are recorded from the Neotropical region. Knowledge about these bugs in northeastern Brazil is relatively poor, with 16 previously recorded species. Here, we present new records for five additional species based on material from the states of Ceará, Maranhão, and Piauí deposited in the Coleção Zoológica do Maranhão, Caxias, Brazil. This increases to 21 the number of species recorded from the region. In addition, we provide photographs, distribution maps, and a key to the fauna of Belostomatidae from northeastern Brazil.

New species of Bryophaenocladius Thienemann, 1934 (Diptera: Chironomidae) from Argentina

Three new species of Bryophaenocladius Thienemann are described and figured as male imagines: B. urbanus sp. n. from Central Argentina, and B. virgotruncatus sp. n. and B. nasus sp. n. from Argentinean Patagonia. A geometric morphometric analysis was performed to evaluate the taxonomic value of the shape of the anal point in species delimitation. The analysis involved 96 species. As a result, the Bryophaenocladius species showed significant anal point patterns of shape change, recovering three main shape types: rounded, equilateral triangle-shaped, and isosceles triangle-shaped. An identification key of the Bryophaenocladius species from the Neotropical region is provided.

Ecomorphology of yellowtail lambari (Characiformes: Characidae) in the neotropical semi-arid region, Brazil

The ecomorphological patterns of the Astyanax lacustris in different environments (lotic and lentic) of the semiarid region of Pernambuco were analyzed using 25 linear morphometric measurements on 240 specimens (120 males and 120 females), with standard lengths ranging from 24.25 to 91.50 mm. These data were converted into 16 ecomorphological attributes and correlated with environmental characteristics. The principal component analysis (PCA) explained 81.64% (first and second components) of the data variation, highlighting sexual dimorphism in specimen size and noticeable variation among individuals of the same sex in different environments. Specimens from lotic environments showed higher caudal peduncle compression index (CPCI) values, while the pectoral fin aspect ration (PFAR) was more pronounced in lentic environments. Overall, females exhibited a wide morphometric variation. Analysis of linear morphometry in different water bodies indicated an intrinsic variation related to hydrodynamics linked to sexual dimorphism and water flow speed. Further studies are suggested to investigate whether factors such as macrophytes and different levels of water depth and flow contribute to this morphometric variation of species in the semi-arid region.

Interactive effects of drought and deforestation on multitrophic communities and aquatic ecosystem functions in the Neotropics-a test using tank bromeliads.

Together with the intensification of dry seasons in Neotropical regions, increasing deforestation is expected to exacerbate species extinctions, something that could lead to dramatic shifts in multitrophic communities and ecosystem functions. Recent studies suggest that the effects of habitat loss are greater where precipitation has decreased. Yet, experimental studies of the pure and interactive effects of drought and deforestation at ecosystem level remain scarce. Here, we used rainshelters and transplantation from rainforest to open areas of natural microcosms (the aquatic ecosystem and microbial-faunal food web found within the rainwater-filled leaves of tank bromeliads) to emulate drought and deforestation in a full factorial experimental design. We analysed the pure and interactive effects of our treatments on functional community structure (including microorganisms, detritivore and predatory invertebrates), and on leaf litter decomposition in tank bromeliad ecosystems. Drought or deforestation alone had a moderate impact on biomass at the various trophic level, but did not eliminate species. However, their interaction synergistically reduced the biomass of all invertebrate functional groups and bacteria. Predators were the most impacted trophic group as they were totally eliminated, while detritivore biomass was reduced by about 95%. Fungal biomass was either unaffected or boosted by our treatments. Decomposition was essentially driven by microbial activity, and did not change across treatments involving deforestation and/or drought. Our results suggest that highly resistant microorganisms such as fungi (plus a few detritivores) maintain key ecosystem functions in the face of drought and habitat change. We conclude that habitat destruction compounds the problems of climate change, that the impacts of the two phenomena on food webs are mutually reinforcing, and that the stability of ecosystem functions depends on the resistance of a core group of organisms. Assuming that taking global action is more challenging than taking local-regional actions, policy-makers should be encouraged to implement environmental action plans that will halt habitat destruction, to dampen any detrimental interactive effect with the impacts of global climate change.

New species, new combinations, and morphological notes of South American Ambrysinae (Heteroptera: Naucoridae)

Although recent studies have been published on Ambrysinae (Naucoridae) from the Neotropical region, few efforts have been made to improve the taxonomic knowledge of this subfamily in Brazil. Two genera of Ambrysinae containing the greatest number of species in South America were recently established to accommodate species previously classified as Ambrysus Stål: Australambrysus Reynoso & Sites and Maculambrysus Reynoso & Sites. The subgeneric classification of Ambrysus has also changed, including the elevation of Melloiella De Carlo back to full generic status. In the present study, three new species of Ambrysinae from Brazil are described, two belonging to Australambrysus and one to Maculambrysus: Australambrysus minutus n. sp., A. tuberculatus n. sp., and Maculambrysus transversus n. sp. In addition, morphological notes are provided for Australambrysus planus (La Rivers) and A. partridgei (De Carlo), the placement of A. fraternus (Montandon) is confirmed, and the following new combinations are proposed: Maculambrysus attenuatus (Montandon) n. comb., and Maculambrysus obscuratus (Montandon) n. comb., species that are transferred from the genus Australambrysus and Ambrysus, respectively. Two of the species treated here (A. fraternus and A. tuberculatus) are included in the Australambrysus plax (La Rivers) species complex, and a morphological redefinition of the complex is presented. Also, the macropterous form and male genitalia of Melloiella truncaticollis De Carlo are described, including new records from southern Brazil.