Variation of cuticular chemical compounds in three species of Mischocyttarus (Hymenoptera: Vespidae) eusocial wasps

Abstract The social wasps have a remarkable system of organization in which chemical communication mediate different behavioral interactions. Among the compounds involved in this process, cuticular hydrocarbons are considered the main signals for nestmate recognition, caste differentiation, and fertility communication. The aims of this study were to describe the cuticular chemical compounds of the species Mischocyttarus consimilis, Mischocyttarus bertonii, and Mischocyttarus latior, and to test whether these chemical compounds could be used to evaluate differences and similarities between Mischocyttarus species, using gas chromatography coupled to mass spectrometry (GC-MS). Workers from these three species presented a variety of hydrocarbons ranging from C17 to C37, and among the compounds identified, the most representative were branched alkanes, linear alkanes and alkenes. The results revealed quantitative and qualitative differences among the hydrocarbon profiles, as confirmed by discriminant analysis. This study supports the hypothesis that cuticular chemical profiles can be used as parameters to identify interspecific and intercolony differences in Mischocyttarus, highlighting the importance of these compounds for differentiation of species and populations.

Aflatoxins produced by Aspergillus nomius ASR3, a pathogen isolated from the leaf-cutter ant Atta sexdens rubropilosa

ABSTRACT Aspergillus spp. cause economic impacts due to aflatoxins production. Although the toxicity of aflatoxins is already known, little information about their ecological roles is available. Here we investigated the compounds produced by Aspergillus nomius ASR3 directly from a dead leaf-cutter queen ant Atta sexdens rubropilosa and the fungal axenic culture. Chemical analyses were carried out by high-resolution mass spectrometry and tandem mass spectrometry techniques. Aflatoxins B1 and G1 were detected in both the axenic culture and in the dead leaf-cutter queen ant. The presence of these mycotoxins in the dead leaf-cutter queen ant suggests that these compounds can be related to the insect pathogenicity of A. nomius against A. sexdens rubropilosa.

Chemical cuticular signature of leafcutter ant Atta sexdens (Hymenoptera, Formicidae) worker subcastes

ABSTRACT In leafcutter ants the division of labour is associated to worker size variation clustered in four subcastes. In this work we used Atta sexdens Forel (1908) as a model to test the hypothesis that each subcaste expresses its own chemical signature comprised of cuticular lipids. To assess it, we extracted epicuticular compounds by using nonpolar solvent hexane and analysed the samples in a combined Gas Chromatography-Mass Spectrometer (GC-MS). We found 24 hydrocarbons with carbon chains ranging from 19 to 39 atoms most of them classified as linear and branched alkanes. No compound occurred in the cuticle of specific worker subcaste, however, the relative proportion pattern varied greatly among them. Our results suggest that although subcastes have similar chemical signatures, significant differences in their relative proportions may play an important role between nestmate and group identification.

Comparative morphology of reproductive and trophic eggs in melipona bees (Apidae, Meliponini)

The process of cell provisioning and oviposition (POP) in stingless bees involves highly complex interactionsbetween the queen and workers. During this process, workers can usually lay two types of eggs, referred toas reproductive and trophic. Reproductive worker-laid eggs are unfertilized but develop into males whereastrophic worker-laid eggs are eaten by the queen immediately after oviposition. Although the egg-layingactivity of reproductive workers varies considerably among species, the laying of trophic eggs appears to bethe rule in Melipona bees. In this work, we examined whether the morphology of eggs laid by workers andqueens of M. scutellaris, M. compressipes fasciculata and M. asilvai was similar to that of other Meliponaspecies. Egg morphology was examined by scanning electron microscopy whereas egg size was measured bylight microscopy. In all of the species studied, the chorion of queen and worker reproductive eggs showed acharacteristic reticulate pattern. The surface of trophic eggs was not reticulate and had an irregular appearancefollowing fixation. Trophic eggs were also invariably smaller than queen-laid eggs and were sometimessmaller than worker-laid reproductive eggs. These findings indicate that trophic eggs can be smaller than theeggs of functional workers, which suggests that the development of this type of egg is probably associatedwith different physiological adaptations.