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Information on the biology of the species in Myrmelachista remains notably scarce. The objective of this study was to report the occurrence, analyze the infl uence of canopy cover on the number of nests in twigs in the litter describe behavioral characteristics of this genus. Hand sampling was performed on trees and twigs deposited in the litter. A total of 84 nests and seven species were found. Myrmelachista ruszkii and M. catharinae were the most frequent and abundant species. In trees, most of the nests were located at the ti ps of dry twigs, and these nests were probably the source of the nests found in the litter of fragments of Atlantic Forest of southeastern Brazil. Canopy cover is associated with the number of nests that were in twigs.Key words: canopy, dense ombrophilous forest, polydomy, reproduction, tree species. RESUMENMyrmelachista es un género neotropical de hormigas arborícolas que nidifi can en cavidades de troncos y ramas. El conocimiento sobre la biología de sus especies es escaso. Este trabajo tuvo como objetivo registrar la ocurrencia, analizar la infl uencia del dosel sobre el número de nidos en ramas en la cama (mezcla de hojas, ramas y tierra) que cubre la selva, y describir las características de comportamiento de Myrmelachista. Se realizaron recolectas manuales de arbóreas y en ramas depositadas en la mezcla anterior. Se encontraron 84 nidos y siete especies Myrmelachista ruszkii y M. catharinae fueron las más frecuentes y abundantes. En las especies arbóreas la mayoría de los nidos se localizan en las extremidades secas de las ramas estos nidos fueron probablemente el origen de los nidos que se encuentran en las camas de los fragmentos de Floresta Atlántica de la región sureste brasileña. El número de nidos en ramas estaría asociado con la cobertura arbórea.Palabras clave: bosque ombrófi lo denso, dosel, especies arbóreas, polidomia, reproducción.

Arboreal ants of the genus Myrmelachista, which have ecologically important relationships with different vegetable species, are found exclusively in the Neotropical region. These ant species are difficult to identify, and their taxonomy remains controversial; moreover, little is known regarding their biology. The objective of the present work is to assess the genetic similarities and dissimilarities between and within Myrmelachista species, with the goal of expanding knowledge of the relationships among the taxa of this genus. Sample collection in selected regions of the dense ombrophile forest of southeastern Brazil yielded 256 nests, which were found in vegetation or among scattered twigs in the leaf litter; eight species were recorded. A total of 180 specimens were analyzed, producing 123 molecular characters. Data analyses revealed similarity relationships that allowed the examined species to be classified into the following groups: (1) Myrmelachista sp. 4, M. nodigera, M. ruszkii and M. gallicola; (2) M. catharinae and M. arthuri; (3) M. reticulata; and (4) Myrmelachista sp. 7. The study results also revealed the existence of two morphological variants of M. catharinae; M. arthuri was more closely related to one of these M. catharinae variants than to the other variant. The present work provides important information regarding genetic variation among Myrmelachista species that may contribute to interpreting the complex morphology of this genus.

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The Neotropical ant genus Myrmelachista Roger comprises 69 described species and subspecies, and still is a poorly studied group. Larvae play a paramount role in colony nutrition in social hymenopterans and bear considerable value in the reconstruction of group phylogenies, however, they are generally neglected. Larvae of different instars of Myrmelachista catharinae Mayr (Hymenoptera: Formicidae) are herein described in detail by light and scanning electron microscopy. The number of larval instars was estimated as three based on the frequency distribution of maximum head capsule widths. The described larvae confirmed some traits typical of the genus: general shape of body and mandibles, general aspect and distribution of body hairs, and the number of sensilla on the palps and galea. Differently from other Myrmelachista larvae previously described, M. catharinae presented two distinct kinds of second instars, some additional types of body hairs, different number of antennal sensilla, and a distinct labrum shape. M. catharinae presented ten pairs of spiracles, which is the first record for this genus.

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