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Pheromones play an important role in the mating behavior of many insects, especially in bees, and it has recently been shown that female Osmia bicornis use the odor bouquet found on male antennae in female choice. Nevertheless, the glandular origin of the substances found on the male antennae is so far unknown. In this study, we investigated if antennal glands exist in males and if they are the glandular source of substances on the antennae’s cuticle, as has been suggested by previous studies. Since electron and light microscopy revealed no such glands, we investigated further possible places of origin for the antennal compounds by conducting chemical analyses of solvent extracts of the male abdominal surface and the antennae, as well as of two glands found in the bee’s head, the labial and mandibular gland. Our results clearly show that the substances found on the abdominal surface and in solvent extracts of the antennae differ significantly in relative amounts. Therefore, the compounds on the antennae must have additional sources. Since the relative amounts of compounds on the surface of antennae are different from the blends on the mandibular gland or the labial gland, neither one of them can be the sole source of the antennal compounds. Hence we believe another glandular source is also involved in the production of the bouquet on the antennae. Especially interesting were high amounts of sterols on the antennae, which also play a role in population differences. This sheds new light on the importance of the antennal compounds and also the importance sterols might play in communication.

Weaver ants (genus Oecophylla) are tropical carnivorous ant species living in high numbers in the canopies of trees. The ants excrete copious amounts of fecal matter on leaf surfaces, and these feces may provide nutrients to host trees. This hypothesis is supported by studies of ant-plant interactions involving other ant species that have demonstrated the transfer of nutrients from ants to plants. In this 7-months study, a GC–MS-based metabolomics approach along with an analysis of total nitrogen and carbon levels was used to study metabolic changes in ant-hosting Coffea arabica plants compared with control plants. The results showed elevated levels of total nitrogen, amino acids, fatty acids, caffeine, and secondary metabolites of the phenylpropanoid pathway in leaves from ant-hosting plants. Minor effects were observed for sugars, whereas little or no effect was observed for organic acids, despite the fact that lower levels of total carbon were found in ant-hosting plants. The increased levels of total nitrogen, amino acids, fatty acids and caffeine and the decreased total carbon were consistent with changes observed in plants grown with an increased supply of nitrogen-containing nutrients. The up-regulation of the phenylpropanoid pathway could indicate biotic stress and/or nutrient deficiency. However, because nutrient deficiency was contradicted by the remaining results, this pathway up-regulation was ascribed to biotic stress caused by the physical presence of the weaver ants.