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Division of labor is one of the most striking features in the evolution of eusociality. Juvenile hormone (JH) mediates reproductive status and aggression among nestmates in primitively eusocial Hymenoptera (species without morphologically distinct castes). In highly social species it has apparently lost its gonadotropic role and primarily regulates the division of labor in the worker caste. Polybia occidentalis, a Neotropical swarm-founding wasp, is an ideal model to understand how JH levels mirror social context and reproductive opportunities because of the absence of a clear morphological caste dimorphism. In this study, we tested the hypothesis that JH influences division of labor, ovary activation and cuticular hydrocarbon profiles of workers. Our observations confirmed that a JH analog (methoprene) and an inhibitor of JH biosynthesis (precocene) affected the cuticular chemical profile associated with age polyethism. Also, methoprene and precocene-I treatment of females influenced ovarian activation differently (individuals treated with methoprene expressed more activated ovaries while precocene treatment did not have significant effect). These results suggest that different hormonal levels induce a differential expression of cuticular chemicals associated with workers' age polyethism, which may be essential for keeping the social cohesion among workers throughout their lives in the colony. Furthermore, JH is likely to play a gonadotropic role in P. occidentalis. JH has apparently undergone certain modifications in social Hymenoptera, presenting multifaceted functions in different species.

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Bees are essential pollinators on earth, supporting forest equilibrium and human agriculture. The chemistry of the stingless bee-plant symbiosis is a complex and not completely understood phenomenon. Here, we combined untargeted tandem mass spectrometry, molecular networking, and multivariate statistical analysis to investigate the chemical diversity in colonies of the stingless bee Scaptotrigona depilis. Flavonoids were the most representative and diverse group of plant metabolites detected, indicating the importance of these biologically active natural products to the bees. We unveiled the metabolome, mapped the distribution of plant metabolites in stingless bee colonies, and digitized the chemical data into a public database.

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Nest temperature is a crucial variable that determines colony survival in social insects. The successful production and development of a new brood, therefore, depends on stable thermal conditions and limited temperature oscillations. Thermoregulatory processes are useful in controlling both individual activity and for the maintenance of colony temperature. We measured heat production generated by nurse bees working on brood combs of the stingless bee Melipona scutellaris (Hymenoptera, Apidae, Meliponini) in this study; our results enabled us to identify the existence of a new task performed by nurse bees, referred to here as 'hot bees' because of their higher thorax surface temperature (4°C above that of other bees within the brood area). This additional heat has been little studied in stingless bees but is likely the result of thorax muscle contractions or, indeed, the development of this musculature as these are recently emerged individuals. We hypothesize that these 'hot bees' contribute to the maintenance of warmth within the nest brood area.

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Ants use pheromones to coordinate their communal activity. Volatile pyrazines, for instance, mediate food resource gathering and alarm behaviors in different ant species. Here we report that leaf-cutter ant-associated bacteria produce a family of pyrazines that includes members previously identified as ant trail and alarm pheromones. We found that L-threonine induces the bacterial production of the trail pheromone pyrazines, which are common for the host leaf-cutter ants. Isotope feeding experiments revealed that L-threonine along with sodium acetate were the biosynthetic precursors of these natural products and a biosynthetic pathway was proposed.

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The larval stage of the stingless bee Scaptotrigona depilis must consume a specific brood cell fungus in order to continue development. Here we show that this fungus is a member of the genus Zygosaccharomyces and provides essential steroid precursors to the developing bee. Insect pupation requires ecdysteroid hormones, and as insects cannot synthesize sterols de novo, they must obtain steroids in their diet. Larval in vitro culturing assays demonstrated that consuming ergosterol recapitulates the developmental effects on S. depilis as ingestion of Zygosaccharomyces sp. cells. Thus, we determined the molecular underpinning of this intimate mutualistic symbiosis. Phylogenetic analyses showed that similar cases of bee-Zygosaccharomyces symbiosis may exist. This unprecedented case of bee-fungus symbiosis driven by steroid requirement brings new perspectives regarding pollinator-microbiota interaction and preservation.

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Many ant and termite colonies are defended by soldiers with powerful mandibles or chemical weaponry. Recently, it was reported that several stingless bee species also have soldiers for colony defence. These soldiers are larger than foragers, but otherwise lack obvious morphological adaptations for defence. Thus, how these soldiers improve colony fitness is not well understood. Robbing is common in stingless bees and we hypothesized that increased body size improves the ability to recognize intruders based on chemosensory cues. We studied the Neotropical species Tetragonisca angustula and found that large soldiers were better than small soldiers at recognizing potential intruders. Larger soldiers also had more olfactory pore plates on their antennae, which is likely to increase their chemosensory sensitivity. Our results suggest that improved enemy recognition might select for increased guard size in stingless bees.

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As in most Hymenoptera, the eusocial stingless bees (Meliponini) have a complementary sex determination (CSD) system. When a queen makes a "matched mating" with a male that shares a CSD allele with her, half of their diploid offspring are diploid males rather than females. Matched mating imposes a cost, since diploid male production reduces the colony workforce. Hence, adaptations preventing the occurrence or attenuating its effects are likely to arise. Here we provide clear evidence that in the stingless bee Scaptotrigona depilis, the emergence of diploid males induces queen death, and this usually occurs within 10-20 days of the emergence of diploid male offspring from their pupae. Queens that have not made a matched mating die when introduced into a colony in which diploid males are emerging. This shows that the adult diploid males, and not the queen that has made a matched mating herself, are the proximate cause of queen death. Analysis of the cuticular hydrocarbon profiles of adult haploid and diploid males shows six compounds with significant differences. Moreover, the diploid and haploid males only acquire distinct cuticular hydrocarbon profiles 10 days after emergence. Our data shows that the timing of queen death occurs when the cuticular hydrocarbons of haploid and diploid males differ significantly, suggesting that these chemical differences could be used as cues or signals to trigger queen death.

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The differentiation of workers into morphological castes represents an important evolutionary innovation that is thought to improve division of labor in insect societies. Given the potential benefits of task-related worker differentiation, it is puzzling that physical worker castes, such as soldiers, are extremely rare in social bees and absent in wasps. Following the recent discovery of soldiers in a stingless bee, we studied the occurrence of worker differentiation in 28 stingless bee species from Brazil and found that several species have specialized soldiers for colony defence. Our results reveal that worker differentiation evolved repeatedly during the last ~ 25 million years and coincided with the emergence of parasitic robber bees, a major threat to many stingless bee species. Furthermore, our data suggest that these robbers are a driving force behind the evolution of worker differentiation as targets of robber bees are four times more likely to have nest guards of increased size than non-targets. These findings reveal unexpected diversity in the social organization of stingless bees.Although common in ants and termites, worker differentiation into physical castes is rare in social bees and unknown in wasps. Here, Grüter and colleagues find a guard caste in ten species of stingless bees and show that the evolution of the guard caste is associated with parasitization by robber bees.

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Animal societies exhibit remarkable variation in their breeding strategies. Individuals can maximize their fitness by either reproducing or by helping relatives. Social hymenopterans have been key taxa for the study of Hamilton's inclusive fitness theory because the haplodiploid sex-determination system results in asymmetric relatedness among breeders producing conflict over the partitioning of reproduction. In small cooperative groups of insects, totipotent individuals may maximize their inclusive fitness by controlling reproduction despotically rather than helping their relatives. Here, we demonstrate that the dominant females of the primitively eusocial bee Euglossa melanotricha (Apidae: Euglossini) control reproduction, but concede part of the reproductive output with their related and unrelated subordinates. As expected, a dominant female capitalizes on the direct reproduction of related subordinates, according to her interests. We found that reproductive skew was positively correlated with relatedness. The concessions were highly reduced in mother-daughter and sibling nests (relatedness r ± s.d. = 0.54 ± 0.02 and 0.79 ± 0.02, respectively) but much more egalitarian in unrelated associations (r = -0.10 ± 0.01). We concluded that reproductive skew in these primitively eusocial bees is strongly related to the genetic structure of associations, and also that females are able to assess pairwise relatedness, either directly or indirectly, and use this information to mediate social contracts.

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Cuticular hydrocarbons (CHCs) are traditionally considered to be one of the most important chemical cues used in the nestmate recognition process of social hymenopterans. However, it has been suggested that in the leafcutter ant genus Atta, it is not the CHCs, but the alarm pheromone that is involved in the nestmate recognition process. In this study we used a laboratory population of Atta sexdens to explore the association between their CHC profile variation and intraspecific aggression. In the first part of the experiment, four colonies were divided into two groups with distinct diets to stimulate differentiation of their CHC profiles. In the second part of the experiment, all colonies received the same diet to examine resemblance of chemical profiles. At the end of each part of the experiment we extracted the CHCs from workers. The results demonstrated that colonies that shared the same food resource had similar cuticular hydrocarbon profiles. Furthermore, colonies were significantly more aggressive towards conspecifics that used a different foliar substrate and consequently had greater differences in their cuticular chemical composition. This study suggests that the CHC profiles of A. sexdens can be affected by the foliar substrates used, and that the CHCs are used in the nestmate recognition process of this species.

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Spiders of the tropical American colonial orb weaver Parawixia bistriata form a communal bivouac in daytime. At sunset, they leave the bivouac and construct individual, defended webs within a large, communally built scaffolding of permanent, thick silk lines between trees and bushes. Once spiders started building a web, they repelled other spiders walking on nearby scaffolding with a "bounce" behavior. In nearly all cases (93%), this resulted in the intruder leaving without a fight, akin to the "bourgeois strategy," in which residents win and intruders retreat without escalated contests. However, a few spiders (6.5%) did not build a web due to lack of available space. Webless spiders were less likely to leave when bounced (only 42% left) and instead attempted to "freeload," awaiting the capture of prey items in nearby webs. Our simple model shows that webless spiders should change their strategy from bourgeois to freeloading satellite as potential web sites become increasingly occupied.

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The capacity to distinguish colony members from strangers is a key component in social life. In social insects, this extends to the brood and involves discrimination of queen eggs. Chemical substances communicate colony affiliation for both adults and brood; thus, in theory, all colony members should be able to recognize fellow nestmates. In this study, we investigate the ability of Dinoponera quadriceps workers to discriminate nestmate and non-nestmate eggs based on cuticular hydrocarbon composition. We analyzed whether cuticular hydrocarbons present on the eggs provide cues of discrimination. The results show that egg recognition in D. quadriceps is related to both age and the functional role of workers. Brood care workers were able to distinguish nestmate from non-nestmate eggs, while callow and forager workers were unable to do so.

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Reproductive conflicts within animal societies occur when all females can potentially reproduce. In social insects, these conflicts are regulated largely by behaviour and chemical signalling. There is evidence that presence of signals, which provide direct information about the quality of the reproductive females would increase the fitness of all parties. In this study, we present an association between visual and chemical signals in the paper wasp Polistes satan. Our results showed that in nest-founding phase colonies, variation of visual signals is linked to relative fertility, while chemical signals are related to dominance status. In addition, experiments revealed that higher hierarchical positions were occupied by subordinates with distinct proportions of cuticular hydrocarbons and distinct visual marks. Therefore, these wasps present cues that convey reliable information of their reproductive status.

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Foraging behaviour has a remarkable significance to colonies of social insects since it is directly related to the supply of food, water, and pulp. Social wasps of the genus Apoica Lepeletier are primarily nocturnal, but studies concerning the general aspects related to this habit are still scarce. This study showed that the rates of foraging flights were higher during the full moon and last quarter moon phases. Frequencies of arrival and departure were correlated with time and temperature at night. The results suggest that the moonlight is an important component to general activities in this genus.

O comportamento de forragear é fundamental para o desenvolvimento das colônias de insetos sociais, pois permite que as colônias sejam supridas de alimento, água e materiais utilizados para a construção dos ninhos. Vespas sociais do gênero Apoica Lepeletier (Hymenoptera: Vespidae) têm comportamento de forrageamento noturno como uma de suas principais características, porém estudos sobre aspectos abióticos que influenciam esse comportamento são ainda escassos. Este estudo mostra que a freqüência de forrageamento foi maior em noites de luas cheia e crescente. Além disso, as saídas e retornos ao ninho correlacionaram-se positivamente com o período da noite e a temperatura. Os resultados sugerem que a luminosidade é um componente importante nas atividades gerais das colônias do gênero.

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