Spatial patterns of movement regulate many aspects of social insect behavior, because how workers move around, and how many are there, determines how often they meet and interact. Interactions are usually olfactory; for example, in ants, by means of antennal contact in which one worker assesses the cuticular hydrocarbons of another. Encounter rates may be a simple outcome of local density: a worker experiences more encounters, the more other workers there are around it. This means that encounter rate can be used as a cue for overall density even though no individual can assess global density. Encounter rate as a cue for local density regulates many aspects of social insect behavior, including collective search, task allocation, nest choice, and traffic flow. As colonies grow older and larger, encounter rates change, which leads to changes in task allocation. Nest size affects local density and movement patterns, which influences encounter rate, so that nest size and connectivity influence colony behavior. However, encounter rate is not a simple function of local density when individuals change their movement in response to encounters, thus influencing further encounter rates. Natural selection on the regulation of collective behavior can draw on variation within and among colonies in the relation of movement patterns, encounter rate, and response to encounters.

Social behavior, although rare, is a highly successful form of living that has reached its most extreme forms in eusocial insects. A tractable framework to understand social evolution is the study of major transitions in social behavior. This includes the transitions between solitary to social living, from species exhibiting intermediate degrees of sociality to species exhibiting true sociality, and from primitive to advanced eusocial species. The latter transition is characterized by the emergence of traits not previously found in primitive eusocial species, such as fixed morphological differences between castes and task specialization within the sterile caste. Such derived traits appear to exist in a binary fashion, present in advanced eusocial species, and absent or rare in primitive ones, and thus do not exist in a gradient that is easily tracked and compared between species. Thus, they may not be viewed as valuable to explore ultimate questions related to social evolution. Here, we argue that derived traits can provide useful insights on social evolution even if they are absent or rare in species with a lower social organization. This applies only if the mechanism underlying the trait, rather than the function it regulates for, can be traced back to the solitary ancestors. We discuss two examples of derived traits, morphological differences in female castes and primer pheromones regulating female reproduction, demonstrating how their underlying mechanisms can be used to understand major transitions in the evolution of social behavior and emphasize the importance of studying mechanistic, rather than functional continuity of traits.

Social insects are biological benchmarks of self-organization and decentralized control. Their integrated yet accessible nature makes them ideal models for the investigation of complex social network interactions, and the mechanisms that shape emergent group capabilities. Increasingly, interindividual heterogeneity, and the functional role that it may play, is seen as an important facet of colonies' social architecture. Insect superorganisms present powerful model systems for the elucidation of conserved trends in biology, through the strong and consistent analogies that they display with multicellular organisms. As such, research relating to the benefits and constraints of heterogeneity in behavior, morphology, phenotypic plasticity, and colony genotype provides insight into the underpinnings of emergent collective phenomena, with rich potential for future exploration. Here, we review recent advances and trends in the understanding of functional heterogeneity within social insects. We highlight the scope for fundamental advances in biological knowledge, and the opportunity for emerging concepts to be verified and expanded upon, with the aid of bioinspired engineering in swarm robotics, and computational task allocation.

Ant colonies are self-organized systems, meaning that complex collective behavior emerges from local interactions among colony members without any central control. Self-organized systems are sensitive to initial conditions, whereby small random effects are amplified through positive feedback and have a large influence on collective outcomes. This sensitivity has been well demonstrated in collective decision-making by ants that use mass recruitment via trail pheromones, where it is attributed to the highly nonlinear relationship between the amount of pheromone on a trail and its effectiveness at attracting recruits. This feature is absent in many species, such as the rock ant Temnothorax rugatulus (Emery) whose tandem run recruitment shows a linear relationship between effort and effectiveness. Thus, these ants may have other behavioral responses that amplify initial differences during collective choices. We investigated this by testing whether nest site selection is influenced by small differences in the amount of brood at competing sites. Our results show that T. rugatulus colonies prefer a nest containing brood items to an empty nest, even when the brood-containing nest has only one brood item. When both nests have brood, colonies prefer the nest that contains more. However, as the numbers of brood items becomes more similar, this preference becomes weaker. Moreover, the smaller the difference in brood number, the more likely are colonies to split between sites. We discuss potential behavioral mechanisms for the observed effect, as well as its implications for number sense in ants.

Social insects are well known for their aggressive (stinging) responses to a nest disturbance. Still, colonies are attacked due to the high-protein brood cached in their nests. Social wasps have evolved a variety of defense mechanisms to exclude predators, including nest construction and coordinated stinging response. Which predatory pressures have shaped the defensive strategies displayed by social wasps to protect their colonies? We reviewed the literature and explored social media to compare direct and indirect (claims and inferences) evidence of predators attacking individuals and colonies of wasps. Individual foraging wasps are predominantly preyed upon by birds and other arthropods, whereas predators on wasp brood vary across subfamilies of Vespidae. Polistinae wasps are predominantly preyed upon by ants and Passeriformes birds, whereas Vespinae are predominantly preyed upon by badgers, bears, and hawks. Ants and hornets are the primary predators of Stenogastrinae colonies. The probability of predation by these five main Orders of predators varies across continents. However, biogeographical variation in prey–predator trends was best predicted by climate (temperate vs. tropical). In social wasps' evolutionary history, when colonies were small, predation pressure likely came from small mammals, lizards, or birds. As colonies evolved larger size and larger rewards for predators, the increased predation pressure likely selected for more effective defensive responses. Today, primary predators of large wasp colonies seem to be highly adapted to resist or avoid aggressive nest defense, such as large birds and mammals (which were not yet present when eusociality evolved in wasps), and ants.

Honey bees utilize their circadian rhythms to accurately predict the time of day. This ability allows foragers to remember the specific timing of food availability and its location for several days. Previous studies have provided strong evidence toward light/dark cycles being the primary Zeitgeber for honey bees. Work in our laboratory described large individual variation in the endogenous period length of honey bee foragers from the same colony and differences in the endogenous rhythms under different constant temperatures. In this study, we further this work by examining the temperature inside the honey bee colony. By placing temperature and light data loggers at different locations inside the colony we measured temperature at various locations within the colony. We observed significant oscillations of the temperature inside the hive, that show seasonal patterns. We then simulated the observed temperature oscillations in the laboratory and found that using the temperature cycle as a Zeitgeber, foragers present large individual differences in the phase of locomotor rhythms for temperature. Moreover, foragers successfully synchronize their locomotor rhythms to these simulated temperature cycles. Advancing the cycle by six hours, resulting in changes in the phase of activity in some foragers in the assay. The results are shown in this study highlight the importance of temperature as a potential Zeitgeber in the field. Future studies will examine the possible functional and evolutionary role of the observed phase differences of circadian rhythms.

Learning and attention allow animals to better navigate complex environments. While foraging, honey bees (Apis mellifera L.) learn several aspects of their foraging environment, such as color and odor of flowers, which likely begins to happen before they evaluate the quality of the food. If bees begin to evaluate quality before they taste food, and then learn the food is depleted, this may create a conflict in what the bee learns and remembers. Individual honey bees differ in their sensitivity to information, thus creating variation in how they learn or do not learn certain environmental stimuli. For example, foraging honey bees exhibit differences in latent inhibition (LI), a learning process through which regular encounter with a stimulus without a consequence such as food can later reduce conditioning to that stimulus. Here, we test whether bees from distinct selected LI genotypes learn differently if reinforced via just antennae or via both antennae + proboscis. We also evaluate whether learned information goes extinct at different rates in these distinct LI genetic lines. We find that high LI bees learned significantly better when they were reinforced both antenna + proboscis, while low LI and control bees learned similarly with the two reinforcement pathways. We also find no differences in the acquisition and extinction of learned information in high LI and low LI bees. Our work provides insight into how underlying cognition may influence how honey bees learn and value information, which may lead to differences in how individuals and colonies make foraging decisions.

The honey bee is an excellent model system to study behavioral ecology, behavioral genetics, and sociogenomics. Nucleic acid-based analyses enable a broad scope of research in functional genomics, disease diagnostics, mutant screening, and genetic breeding. Multiple levels of analysis lead to a more comprehensive understanding of the causes of phenotypic variation by integrating genomic variation, transcriptomic profiles, and epigenomic information. One limitation, however, is the sample preparation procedures to obtain high quality DNA and RNA simultaneously, particularly from small amounts of material, such as tissues of individual bees. We demonstrate that it is feasible to perform dual extractions of DNA and RNA from a single individual bee and compare the quality and quantity of the extracted nucleic acids using two different types of methods. There was a greater total yield of DNA and RNA from ethanol-based extractions with minimal differences in overall concentration in ng/uL. We describe here the first validated method for dual extraction of DNA and RNA specifically from individual honey bees (Apis mellifera).

Most honey bee (Apis mellifera Linnaeus, 1758) (Hymenoptera: Apidae) colonies in the United States have been exposed to the beekeeper-applied miticides amitraz, coumaphos, and tau-fluvalinate. Colonies are also often exposed to agrochemicals, which bees encounter on foraging trips. These and other lipophilic pesticides bind to the beeswax matrix of comb, exposing developing bees. We explored whether queen-rearing beeswax containing pesticides affects the reproductive health of mated queens. We predicted that queens reared in pesticide-free beeswax would have higher mating frequencies and sperm viability of stored sperm compared with queens reared in wax containing pesticides. Mating frequency and sperm viability are two traditional measurements associated with queen reproductive health. To test these hypotheses, we reared queens in beeswax-coated cups that were pesticide free or contained field-relevant concentrations of 1) amitraz, 2) a combination of tau-fluvalinate and coumaphos, or 3) a combination of the agrochemicals chlorothalonil and chlorpyrifos. We then collected queens once they mated to determine sperm viability, using a dual fluorescent cell counter, and mating frequency, genotyping immature worker offspring at eight polymorphic microsatellite loci. Sperm viability did not differ between control queens and those reared in pesticide-laden wax. However, queens exposed to amitraz during development exhibited higher mating frequency than queens reared in pesticide-free beeswax or beeswax containing the other pesticide combinations. Our results suggest that miticide exposure during development affects queen mating frequency but not sperm viability, at least in newly mated queens. This finding, which has practical implications for commercial queen rearing and overall colony health, calls for further study.

Male hymenopterans do not typically provide help with nest construction or maintenance. This is thought to be due to the decreased relatedness of males to their siblings compared to sisters, and selection for outbreeding resulting in male dispersal from natal nesting sites. However, some instances of male ‘helping’ behaviors have been observed and can usually be explained by increased access to mating with resident females. Here we report on the first observations of cohabiting males within the nests of reproductive females of the facultatively social small carpenter bee, Ceratina australensis. Social nesting in C. australensis occurs at a consistently low rate across populations. We used microsatellites markers to determine relatedness, combined with 3 yr of nest demographic data collected across three populations, to assess the relative fitness of reproductive, nonreproductive, and male individuals cohabiting in reproductive nests. We found that males were brothers of reproductive females, both remaining in their natal nest. However, there was no evidence that they were mating with their sisters across all nests observed. Males in reproductive nests did not gain any direct or indirect fitness benefits as they did not sire any brood and their presence did not increase brood productivity or survivorship. It is possible that males were waiting to mate with nieces who had not yet emerged. Why males were tolerated remains unknown. Mating biology is an important consideration in social theory which requires additional empirical studies. Future long-term studies are needed to capture unusual social behaviors including male nesting behaviors.

Social behavior has been predicted to select for increased neural investment (the social brain hypothesis) and also to select for decreased neural investment (the distributed cognition hypothesis). Here, we use two related bees, the social Augochlorella aurata (Smith) (Hymenoptera: Halictidae) and the related Augochlora pura (Say), which has lost social behavior, to test the contrasting predictions of these two hypotheses in these taxa. We measured the volumes of the mushroom body (MB) calyces, a brain area shown to be important for cognition in previous studies, as well as the optic lobes and antennal lobes. We compared females at the nest foundress stage when both species are solitary so that brain development would not be influenced by social interactions. We show that the loss of sociality was accompanied by a loss in relative neural investment in the MB calyces. This is consistent with the predictions of the social brain hypothesis. Ovary size did not correlate with MB calyx volume. This is the first study to demonstrate changes in mosaic brain evolution in response to the loss of sociality.

In social insects, the reproductive division of labor is often regulated through communication using cuticular hydrocarbons (CHCs) that indicate caste identity and reproductive status. In many termites, workers retain reproductive potential and can differentiate into ergatoid reproductives, and this process is mediated by the presence of reproductives in sex- and age-specific patterns. However, little is known about the variation of CHCs profiles during this transition. In this study, we analyzed the CHC profiles of workers in comparison with ergatoids of different age, sex, and mating status in the eastern subterranean termite, Reticulitermes flavipes (Kollar) (Blattodea: Rhinotermitidae), one of the most widely distributed termite species in the world. Both female and male ergatoids were characterized by the presence of tricosane and a group of long-chain and methyl-branched hydrocarbons (chain length ≥ 33), which were found in significantly lower quantities from workers. In addition, CHC profiles differed between newly differentiated (3–4 d) and old (20–25 d) ergatoids, but no difference in CHC signatures was found between females and males based on identified compounds. Heneicosane, a previously reported royal recognition pheromone in R. flavipes, was not detected in ergatoids examined in this study. The results of caste- and age-dependent variations suggest that CHCs may act as releaser pheromones that mediate caste recognition and age-related interactions between reproductives, but analytical results of identified compounds in this study do not support CHCs as sex-specific primer pheromones that regulate nestmate fertility. Royal pheromones in termites may involve complex hydrocarbon blends and non-hydrocarbon substances that await further investigation.

Social insects produce complex nest structures as a result of the repetition of simple behaviors by many individuals. Individual actions are often consistent across different socio-environmental conditions, which enables colonies to build a variety of structures with minimal change in behavior. In this study, we show that the individual building behavior of termites can be a species-specific trait shared even between distinct morphological castes. Subterranean termites engage in soil excavation in two different contexts in their life history: foraging for resources by workers and initial nest excavation by colony foundation pairs. Our comparison of tunneling behaviors by colony founders of three different species revealed distinct transporting mechanisms; Heterotermes aureus (Snyder) (Isoptera: Rhinotermitidae) and Gnathamitermes perplexus (Banks) (Isoptera: Termitidae) carry sand particles using only their mandibles, while Paraneotermes simplicicornis (Banks) (Isoptera: Kalotermitidae) use their legs to kick sand particles backward. The observed behaviors are consistent with those of workers in each species, despite a substantial dimorphism of body size, especially in G. perplexus. Furthermore, the behavioral difference is associated with distinct tunnel development and task allocation patterns among species. Our study suggests that the nest building behavior of termites varies little with context or function within a species but can change among species, emphasizing the fruitfulness of comparative studies in future research.

Corpse management is essential for social animals to maintain colony health. In the eastern subterranean termite, Reticulitermes flavipes, workers carry out undertaking behaviors to mitigate the risks associated with the dead. In this study, we hypothesized that termites would respond differently to the corpses from different castes based on their postmortem chemical signatures. To test this hypothesis, we 1) documented the behavioral responses of the workers toward corpses from different castes, and 2) profile the chemical signatures of these corpses. Corpses from all castes were retrieved inside the nests and cannibalized when they were decomposed <64 h, regardless of the presence or absence of the cues that we refer to as early death cues (3-octanol and 3-octanone). However, after 64 h, all corpses except for soldiers were buried on site by R. flavipes workers. The late death cues (oleic acid) were cumulative over time among castes but accumulated more slowly and at lower levels in soldiers. The differential release of 3-octanol and 3-octanone between workers/soldiers and nymphs could be explained by either qualitative or quantitative differences in signaling the death between imaginal and neuter developmental pathways. In summary, the efficient and selective recognition of the dead and the fine-tuning of subsequent undertaking responses observed in R. flavipes are aspects of corpse management, which can minimize the potential risks associated with different castes and maximize the colony fitness.