Social animals must communicate to define group membership and coordinate social organization. For social insects, communication is predominantly mediated through chemical signals, and as social complexity increases, so does the requirement for a greater diversity of signals. This relationship is particularly true for advanced eusocial insects, including ants, bees, and wasps, whose chemical communication systems have been well-characterized. However, we know surprisingly little about how these communication systems evolve during the transition between solitary and group living. Here, we demonstrate that the sensory systems associated with signal perception are evolutionarily labile. In particular, we show that differences in signal production and perception are tightly associated with changes in social behavior in halictid bees. Our results suggest that social species require a greater investment in communication than their solitary counterparts and that species that have reverted from eusociality to solitary living have repeatedly reduced investment in these potentially costly sensory perception systems.

To begin to explore the role of biogenic amines in reproductive division of labor in social insects, brain levels of dopamine, serotonin, and octopamine were measured in bumble bee (Bombus terrestris) workers and queens that differ in behavioral and reproductive state. Levels of all three amines were similar for mated and virgin queens. Young workers that developed with or without a queen had similar amine levels, but in queenright colonies differences in biogenic amine levels were associated with differences in behavior and reproductive physiology. Dominant workers had significantly higher octopamine levels compared with workers of lower dominance status but of similar size, age, and ovary state. High dopamine levels were associated with the last stages of oocyte development irrespective of worker social status and behavior. These results suggest that biogenic amines are involved in behavioral and physiological aspects of regulation of reproduction in bumble bees.

Abstract. Ant colonies experience continuous shifts in worker populations, which may affect odour composition in the nest. A major question regarding the dynamics of gestalt formation is that of the speed at which the scent of a new individual will be incorporated into the gestalt. It is predicted from the gestalt model of colony odour that workers have to exchange recognition cues continuously to maintain themselves within the gestalt and become well integrated within their colony. Using radioactive tracers the rates of transfer were measured between a labelled donor ant and one or 10 recipient ants, as a close approximation to the within‐nest situation. The labelled hydrocarbons were first transferred to a small number of individuals and progressively to all the individuals of the group so that the distribution of hydrocarbon transfer rate approached a normal distribution. Furthermore, in Camponotus fellah Dalla Torre, which performs trophallaxis, homogeneity was reached more rapidly than in Aphaenogaster senilis Mayr, which does not show this behaviour. In the latter species, the gestalt seems to be maintained mainly by allogrooming. These experiments were accompanied by behavioural observations to ascertain the respective importance of trophallaxis and allogrooming in the behavioural time‐budget of the ants. In A. senilis, allogrooming was more frequent than in ants that trophallax, which corroborates the role of allogrooming in the establishment of the gestalt in this species.

The mechanisms of competition and resource domination were analysed in the Mediterranean ant Camponotus cruentatus. In a plot located in southern Spain mature colonies are overdispersed, which is indicative of territoriality in other species. Unexpectedly, however, workers from neighbouring colonies commonly foraged in areas that overlapped by more than 44%. This suggests that while mature colonies possibly prevent the establishment of new colonies in the vicinity of their nests, they do not limit the intrusion of alien foragers. In contrast, rich food sources located in common foraging areas are aggressively defended, generally leading to their domination by the nest that discovered them first. Resource exploitation further requires rapid recruitment of foragers and soldiers to transport food as well as to exclude competitors. Complementary to the field experiments we conducted laboratory bioassays to assess intercolonial aggression. Group encounters showed that workers of C. cruentatus were equally aggressive towards alien ants irrespective of whether they were sympatric neighbours (and had possibly had contact), sympatric nonneighbours (which had probably had no contact), or allopatric. This was corroborated by analysis of the hydrocarbons that generally serve as colony recognition cues. This mixture, which contains an unusual proportion of trimethylalkanes, showed important colony specificity. The high intraspecific aggression shown indiscriminately by workers indicates that the 'dear enemy' effect does not exist in this species and suggests that scarce resources are worth defending against intraspecific competitors. We discuss several proximate and ultimate constraints that may prevent the general occurrence of this process in ants.

Within and between individuals hydrocarbon (HC)-circulation was studied in Pachycondyla apicalis workers, using radioactive labeling. Newly synthesized HCs occurred both in the PPG and on the epicuticle in appreciable amounts, lesser quantities were found in the crop. The front basitarsal brush contained a greater amount of radiolabeled HCs than could be predicted from its surface area, suggesting preferential secretion to these organs. We propose that the newly synthesized HCs are secreted primarily to the front basitarsal brushes and are thereafter either distributed throughout the body surface, or cleared via the PPG and the alimentary canal.Using labeled HCs as a model, we tracked the timedependent dispersion of cuticular lipids among 11 workers, one of which was prelabeled for 24 hours. Distribution among the recipients became progressively uniform, reaching near homogenization between 5 -10 days. The mean HCs transfer of P. apicalis to the PPG was substantially lower compared to that of Camponotus fellah or Aphaenogaster senilis. In contrast, transfer to the cuticle in this species was superior. We attribute the low transfer to the PPG to the inefficacy of passive body contact characteristic of P. apicalis, as opposed to trophallaxis and/or allogrooming that typify the other two species. The higher occurrence of radiolabeled HCs in P. apicalis cuticle can be attributed to their accumulation in the basitarsal brushes. The impact of cuticular lipid transfer and formation of uniform colony odour, as opposed to the maintenance of an idiosyncratic caste-specific composition, are discussed.