Anatomy and histology of the metapleural gland in the giant tropical ant Paraponera clavata (Fabricius, 1775) (Formicidae: Paraponerinae).

Ants are social insects with about 85 exocrine glands with different morphologies. The metapleural gland is exclusive to ants and its compounds have antimicrobial action, indicating a function in the defense against pathogens. Within ants, Paraponera clavata is the only living species representative of Paraponerinae. This study describes the anatomy and histology of the metapleural gland in workers of P. clavata. The metapleural gland is formed by secretory units that release secretion in a reservoir through collecting canaliculi. Secretory units are bicellular with a well-developed globular secretory cell, with 145 µm in diameter, and a duct cell forming the collecting canaliculi characterizing a class III gland. The metapleural gland is pointed out as a synapomorphy of ants. Paraponerinae constitutes one of the six subfamilies of the basal and paraphyletic Poneroide clade and knowledge of the metapleural gland morphology contribute to the understanding of evolutionary history of the basal ants' groups.

Sperm morphology of Elasmus polistis Burks, 1971 (Hymenoptera: Chalcidoidea: Eulophidae).

The sperm morphology of the parasitoid Elasmus polistis (Eulophidae) has been investigated with light and transmission electron microscopy. The sperm were filiform and spiraled, with 165.6 (± 4.6) µm in length, and showed a distinctive head, formed by a one-layered small acrosome and a nucleus, and a flagellar region. An extracellular sheath from which many long filaments radiated out covered the acrosome and part of the nucleus. The spiral nucleus, with 24.1 (± 1.3) µm in length, was filled with homogeneously compact chromatin. In the nucleus-flagellum transition, the centriole adjunct extended posteriorly from the nuclear base in a spiral around the basal body, which has two central microtubules, and axoneme for approximately 1.1 µm. The two mitochondrial derivatives began roughly at the same level and at the base of the centriole adjunct. In cross-section, they were symmetrical, with a slightly oval shape and a smaller diameter in comparison to the axoneme. The latter, also spiraled, consisted of 9 + 9 + 2 microtubules that was formed from the basal body situated just below and aligned with the nucleus. The E. polistis sperm showed the same basic structures and morphological characteristics as observed in other Chalcidoidea. However, it was possible to distinguish the sperm of this species from those of other Eulophidae by (i) the long length of the centriole adjunct on the flagellum, and (ii) the presence of two central microtubules within the basal body. The sperm characteristics suggest that Eulophidae is closely related to Trichogrammatidae and both families are more similar to Eurytomidae, Pteromalidae, and Torymidae than Agaonidae.

Deltamethrin-Mediated Toxicity and Cytomorphological Changes in the Midgut and Nervous System of the Mayfly Callibaetis radiatus.

Immature instars of mayflies are important constituents of the food web in aquatic ecosystems (especially in Neotropical regions) and they are among the most susceptible arthropods to pyrethroid insecticides. These insecticides have been recognized as important stressors of freshwater ecosystems, but their cellular effects in aquatic insects have been neglected. Here, we assessed the susceptibility to deltamethrin (a typical type II pyrethroid) as well as the deltamethrin-mediated cytomorphological changes in the central nervous system and midgut of the mayfly Callibaetis radiatus. While the deltamethrin LC50 for 24 h of exposure was of 0.60 (0.46-0.78) µg of a.i/L, the survival of C. radiatus was significantly reduced in deltamethrin concentrations ≥ 0.25 µg a.i/L at 96 h of exposure. Sub-lethal deltamethrin exposure severely affected the cytomorphology of C. radiatus midgut (e.g., muscle layer retraction, cytoplasm vacuolation, nucleus and striated border disorganization) and also induced slight cytomorphological changes in the brain (e.g., presence of pyknotic nuclei) and in the thoracic ganglia (e.g., vacuolation of neurons and presence of pyknotic nuclei) of these insects. However, DNA damage was absent in all of these organs, suggesting that the sublethal cellular stress induced by deltamethrin might disrupt physiological processes (e.g., metabolism or electrical signal transmission) rather than cause cell death (e.g., apoptosis) in C. radiatus. Thus, our findings indicated that deltamethrin actions at cellular levels represent a clear indication of sublethal effects on the C. radiatus survival abilities.