Morphological and morphometric studies of the antennal sensilla from two populations of Atta robusta (Borgmeier 1939) (Hymenoptera: Formicidae) / Estudo morfológico e morfométrico das sensilas antenais de Atta robusta (Borgmeier 1939) (Hymenoptera: Formicidae)

The ant Atta robusta is endemic to the “restinga” ecosystems where it has an important role in the dynamics of seed dispersal. Despite its importance, A. robusta is considered a threatened species. In this study we analyzed the antennal sensory organs of two different populations of A. robusta (from the cities of São Mateus and Maricá in in Espírito Santo and Rio de Janeiro States, respectively) using a scanning electron microscope (SEM). SEM revealed different types of sensilla in the A. robusta antennae, i.e., curved and straight trichoid, basiconic, ampullacea and coeloconic, which were highly abundant found in the distal flagellomeres (F) compared with other antenna regions. There were differences in samples collected from two locations in terms of the sensilla number and length. The average numbers of straight and curved trichoid sensillae numbers were different in F9 and F8, respectively, while the average length of the curved trichoid sensilla was only different in F9. These variations in sensory organs between two populations of A. robusta may indicate an adaptation of this species to different environmental conditions. The number of straight trichoid sensilla was only significantly different in F9.

Atta robusta é uma espécie de formiga endêmica, com papel importante na dinâmica dos ecossistemas de restinga. Apesar de sua importância como dispersora de sementes nesse tipo de ecossistema, essa espécie encontra-se ameçada de extinção. O presente trabalho lançou mão da microscopia eletrônica de varredura (MEV) para descrever as sensilas antenais de A. robusta e investigar diferenças entre sensilas antenais dessa espécie em indivíduos coletados em localidades diferentes, nos municípios de São Mateus (Estado do Espírito Santo) e Maricá (Estado do Rio de Janeiro). Diferentes tipos de sensilas como tricoideas retas e curvadas, basicônicas, ampuláceas e celocônicas foram encontradas nas antenas, sendo que todas são mais numerosas no flagelomero nove (F9) ou mais distal. Houve diferença em número e em comprimento das sensilas tricoideas retas e curvatas em F8 e F9 entre os indivíduos das duas localidades. Os números médios das sensilas tricoides retas e curvadas foram diferentes para os F9 e F8, respectivamente, enquanto que o comprimento médio das sensilas tricoides curvadas foi diferente para o F9. Essa variação na quantidade de sensilas antenais entre as populações é, possivelmente, uma plasticidade fenotípica, característica importante para a adaptação de espécies a variações ambientais. Esse trabalho representa um estudo preliminar na tentativa de se estudar a variação nos órgãos sensoriais entre diferentes populações de A. robusta.

Description of the immatures of Linepithema humile Mayr (Hymenoptera: Formicidae)

Linepithema humile Mayr is an ant species originally native to South America that has been spread accidently throughout the globe through international trade. It is a serious urban and crop pest. Despite its economic importance, little is known about the larvae of this species apart from a brief description based on a few specimens. The present investigation is aimed at describing every immature stage of L. humile. Three larval instars were determined through the frequency distribution of the maximum width of head capsules from a sample of 525 larvae. The morphological descriptions were based on 150 eggs, 70 larvae, and 90 pupae examined by light and scanning electron microscopy. Some morphological characteristics reported to be typical of Linepithema Mayr larvae were confirmed - dolichoderoid body shape, presence of dorsal protuberance, sparse simple body hairs, presence of nine pairs of spiracles and dolichoderoid mandibles. We concluded that an earlier published description was based on queen larvae, and that the protuberance is only present in worker larvae. The information provided in this study may aid ant systematics and phylogenetics, as well provide a better understanding of the biology of this species.