Daily rhythms related to distinct social tasks inside an eusocial bee colony

A bee colony is often compared to a multicellular organism, mainly because of its spatial organization. We propose that a temporal organization of equal importance is also present. To support this view, we studied the reproductive processes of two closely related species of stingless bees. Stingless bees enable observations of daily rhythms that are performed by distinct social classes. The emergent process, POP, is cyclic and consists of the building and provisioning of brood cells by the worker bees and egg-laying by the queen. Colonies were kept in the laboratory under constant conditions with the exit tube opening to the environment; thus, foragers had direct access to environmental cycles. At a later stage of the experiment, the exit tube was closed by a sieve; in this case, bees had their own stock of food, but the environmental LD cycle could still be detected when they were inside the exit tube. Daily POP rhythms were present and showed distinct temporal patterns in each species. A third condition was imposed on one of the species only: the exit tube was closed by a sieve and maintained inside a box that was provided with constant illumination. In this colony, the POP rhythm was perturbed by the destruction of the brood cells. Restoration of POP consisted of a rapid reconstruction of cells followed by a late oviposition in the same day. As different rhythmic patterns were detected, but showed regular timings with respect to one another, an interpretation based upon the concept of an internal temporal order is suggested.     

Circadian Activity Rhythm of the Foragers of a Eusocial Bee (Scaptotrigona aff depilis,Hymenoptera, Apidae,Meliponinae) outside the Nest

In all bee colonies of the Meliponinae subfamily, activity inside the nest is temporally organized around the oviposition by the queen, assisted by nurse bees. This class is constituted by young bees that remain inside the nest. In a colony of Scaptotrigona aff depilis, the oviposition cycle occurs in a 3-hour period. The foragers are older bees that collect food for the colony in the field. Other tasks in the nest are performed by workers of ages intermediate between nurses and foragers. With the aim of studying activity rhythms, foragers were kept under constant light, with food constantly available and no flight restriction. The results showed that, although inside the nest the prevailing period is 3 hours, the activity of the foragers is a circadian rhythm, synchronized by the light/dark cycle and probably influenced by other environmental cycles as temperature and the availability of food sources.     

The colony environment, but not direct contact with conspecifics, influences the development of circadian rhythms in honey bees

Honey bee (Apis mellifera) workers emerge from the pupae with no circadian rhythms in behavior or brain clock gene expression but show strong rhythms later in life. This postembryonic development of circadian rhythms is reminiscent of that of infants of humans and other primates but contrasts with most insects, which typically emerge from the pupae with strong circadian rhythms. Very little is known about the internal and external factors regulating the ontogeny of circadian rhythms in bees or in other animals. We tested the hypothesis that the environment during early life influences the later expression of circadian rhythms in locomotor activity in young honey bees. We reared newly emerged bees in various social environments, transferred them to individual cages in constant laboratory conditions, and monitored their locomotor activity. We found that the percentage of rhythmic individuals among bees that experienced the colony environment for their first 48 h of adult life was similar to that of older sister foragers, but their rhythms were weaker. Sister bees isolated individually in the laboratory for the same period were significantly less likely to show circadian rhythms in locomotor activity. Bees experiencing the colony environment for only 24 h, or staying for 48 h with 30 same-age sister bees in the laboratory, were similar to bees individually isolated in the laboratory. By contrast, bees that were caged individually or in groups in single- or double-mesh enclosures inside a field colony were as likely to exhibit circadian rhythms as their sisters that were freely moving in the same colony. These findings suggest that the development of the circadian system in young adult honey bees is faster in the colony than in isolation. Direct contact with the queen, workers, or the brood, contact pheromones, and trophallaxis, which are all important means of communication in honey bees, cannot account for the influence of the colony environment, since they were all withheld from the bees in the double-mesh enclosures. Our results suggest that volatile pheromones, the colony microenvironment, or both influence the ontogeny of circadian rhythms in honey bees.     

The involvement of the antennae in mediating the brood influence on circadian rhythms in "nurse" honey bee (Apis mellifera) workers

Age-related division of labor in honey bees is associated with plasticity in circadian rhythms. Forager bees that are typically older than 3 weeks of age show strong behavioral and molecular circadian rhythms with higher activity during the day. Younger bees that typically care for ("nurse") the brood are active around the clock with similar brain clock gene levels throughout the day. However, nurses that are caged on brood-less combs inside or outside the hive show robust circadian rhythms with higher activity during the day, suggesting that direct contact with the brood mediates the plasticity in the circadian system. The nature of the brood signals affecting the workers' circadian system and the modalities by which they are detected are unknown. Given that the antennae are pivotal sensory organs in bees, we hypothesized that they are involved in mediating the brood influence on the plasticity in circadian rhythms. The flagella of the antennae are densely covered with diverse sensory structures able to detect a wide range of signals. To test our hypothesis, we removed the flagella of nurses and observed their behavior in isolation and in free-foraging colonies. We found that individually-isolated flagella-less bees under constant laboratory conditions show robust circadian rhythms in locomotor activity. In observation hives, flagella-less bees cared for the brood, but were more active during the day. By contrast, sham-treated bees were active around the clock as typical of nurses. Detailed video recordings showed that the brood-tending behavior of flagella-less and sham-treated bees is similar. These observations suggest that the difference in the patterns of brood care activity is not because the flagella-less bees did not contact the brood. Our results suggest that nurses are able to find the brood in the dark environment of the hive without their flagella, perhaps by using other sensory organs. The higher activity of flagella-less bees during the day further suggests that the flagella are involved in mediating the brood signals modulating plasticity in the circadian system.     

Honeybee Colony Thermoregulation – Regulatory Mechanisms and Contribution of Individuals in Dependence on Age,Location and Thermal Stress

Honeybee larvae and pupae are extremely stenothermic, i.e. they strongly depend on accurate regulation of brood nest temperature for proper development (33–36°C). Here we study the mechanisms of social thermoregulation of honeybee colonies under changing environmental temperatures concerning the contribution of individuals to colony temperature homeostasis. Beside migration activity within the nest, the main active process is “endothermy on demand” of adults. An increase of cold stress (cooling of the colony) increases the intensity of heat production with thoracic flight muscles and the number of endothermic individuals, especially in the brood nest. As endothermy means hard work for bees, this eases much burden of nestmates which can stay ectothermic. Concerning the active reaction to cold stress by endothermy, age polyethism is reduced to only two physiologically predetermined task divisions, 0 to ∼2 days and older. Endothermic heat production is the job of bees older than about two days. They are all similarly engaged in active heat production both in intensity and frequency. Their active heat production has an important reinforcement effect on passive heat production of the many ectothermic bees and of the brood. Ectothermy is most frequent in young bees (<∼2 days) both outside and inside of brood nest cells. We suggest young bees visit warm brood nest cells not only to clean them but also to speed up flight muscle development for proper endothermy and foraging later in their life. Young bees inside brood nest cells mostly receive heat from the surrounding cell wall during cold stress, whereas older bees predominantly transfer heat from the thorax to the cell wall. Endothermic bees regulate brood comb temperature more accurately than local air temperature. They apply the heat as close to the brood as possible: workers heating cells from within have a higher probability of endothermy than those on the comb surface. The findings show that thermal homeostasis of honeybee colonies is achieved by a combination of active and passive processes. The differential individual endothermic and behavioral reactions sum up to an integrated action of the honeybee colony as a superorganism.     

The evolution of activity breaks in the nest cycle of annual eusocial bees: a model of delayed exponential growth

Background  

Social insects show considerable variability not only in social organisation but also in the temporal pattern of nest cycles. In annual eusocial sweat bees, nest cycles typically consist of a sequence of distinct phases of activity (queen or workers collect food, construct, and provision brood cells) and inactivity (nest is closed). Since the flight season is limited to the time of the year with sufficiently high temperatures and resource availability, every break reduces the potential for foraging and, thus, the productivity of a colony. This apparent waste of time has not gained much attention.     

Mapping Sleeping Bees within Their Nest: Spatial and Temporal Analysis of Worker Honey Bee Sleep

Patterns of behavior within societies have long been visualized and interpreted using maps. Mapping the occurrence of sleep across individuals within a society could offer clues as to functional aspects of sleep. In spite of this, a detailed spatial analysis of sleep has never been conducted on an invertebrate society. We introduce the concept of mapping sleep across an insect society, and provide an empirical example, mapping sleep patterns within colonies of European honey bees (Apis mellifera L.). Honey bees face variables such as temperature and position of resources within their colony''s nest that may impact their sleep. We mapped sleep behavior and temperature of worker bees and produced maps of their nest''s comb contents as the colony grew and contents changed. By following marked bees, we discovered that individuals slept in many locations, but bees of different worker castes slept in different areas of the nest relative to position of the brood and surrounding temperature. Older worker bees generally slept outside cells, closer to the perimeter of the nest, in colder regions, and away from uncapped brood. Younger worker bees generally slept inside cells and closer to the center of the nest, and spent more time asleep than awake when surrounded by uncapped brood. The average surface temperature of sleeping foragers was lower than the surface temperature of their surroundings, offering a possible indicator of sleep for this caste. We propose mechanisms that could generate caste-dependent sleep patterns and discuss functional significance of these patterns.     

Does time spent on adult bees affect reproductive success of Varroa mites?

Reproduction ofVarroa jacobsoni Oudemans (Acari: Varroidae) and the number ofVarroa mites that were found dead on the bottom board of the hive, were studied in relation to the period the mites spent on adult honey bees,Apis mellifera L. (Hymenoptera: Apidae), prior to invasion into brood cells. The maximum period on adult bees was 23 days. To introduce mites, combs with emerging worker brood, heavily infested with mites, were placed into a colony and removed the next day. At the beginning of the first day following emergence from brood cells, 18% of the mites introduced into the colony was found on the bottom of the hive. Part of these mites may already have died inside the capped brood cells, and then fallen down after cleaning of cells by the bees. At the second and third day following emergence, respectively 4% and 2% of the mites on adult bees at the previous day was recovered on the bottom, whereas from the fourth day on only 0.6% of the mites on adult bees was recovered on the bottom per day. After invasion into brood cells, 8–12% of the mites did not produce any offspring. Of the mites that did reproduce, the total number of offspring was 4.0–4.4 per mite during one reproductive cycle, part of which may reach maturity resulting in 1.2–1.3 viable daughters, and 8–10% of the mites produced only male offspring. Reproduction was independent of the period the mites had spent on adult bees prior to invasion into brood cells.     

Circadian Locomotor Activity in Freshwater Decapods: An Ecological Approach

Circadian rhythms of locomotor activity shown by freshwater decapods display different patterns among crayfish, Procambarus, and crabs, when exposed to artificial light-dark cycles. Crayfish are mainly nocturnal while a crepuscular activity is observed in crabs of the genus Pseudothelphusa. In constant darkness, free running rhythms are displayed in unimodal or bimodal patterns by crayfish Procambarus; however, Pseudothelphusa continues to show bimodal rhythms. The many studies using locomotor activity indicate that the rhythm in freshwater crabs is circadian in nature, but that a multioscillatory system may be controlling the overt rhythm. In the present study, the implications of different locomotor activity patterns are analyzed in selected freshwater decapods with regard to the interactions between light and the organisms. Crabs and crayfish are commonly found in similar habitats, often sharing the same environment; however, different patterns of locomotor activity as well as different sensitivities of the bouts of activity with regard to entrainment by light, indicate that distinct temporal niches may exist that result in temporal exclusion or low competition.     

Egg‐size plasticity in Apis mellifera: Honey bee queens alter egg size in response to both genetic and environmental factors

Social evolution has led to distinct life‐history patterns in social insects, but many colony‐level and individual traits, such as egg size, are not sufficiently understood. Thus, a series of experiments was performed to study the effects of genotypes, colony size and colony nutrition on variation in egg size produced by honey bee (Apis mellifera) queens. Queens from different genetic stocks produced significantly different egg sizes under similar environmental conditions, indicating standing genetic variation for egg size that allows for adaptive evolutionary change. Further investigations revealed that eggs produced by queens in large colonies were consistently smaller than eggs produced in small colonies, and queens dynamically adjusted egg size in relation to colony size. Similarly, queens increased egg size in response to food deprivation. These results could not be solely explained by different numbers of eggs produced in the different circumstances but instead seem to reflect an active adjustment of resource allocation by the queen in response to colony conditions. As a result, larger eggs experienced higher subsequent survival than smaller eggs, suggesting that honey bee queens might increase egg size under unfavourable conditions to enhance brood survival and to minimize costly brood care of eggs that fail to successfully develop, and thus conserve energy at the colony level. The extensive plasticity and genetic variation of egg size in honey bees has important implications for understanding life‐history evolution in a social context and implies this neglected life‐history stage in honey bees may have trans‐generational effects.     

Reproduction of Varroa destructor in worker brood of Africanized honey bees (Apis mellifera)

Reproduction and population growth of Varroa destructor was studied in ten naturally infested, Africanized honeybee (AHB) (Apis mellifera) colonies in Yucatan, Mexico. Between February 1997 and January 1998 monthly records of the amount of pollen, honey, sealed worker and drone brood were recorded. In addition, mite infestation levels of adult bees and worker brood and the fecundity of the mites reproducing in worker cells were determined. The mean number of sealed worker brood cells (10,070 ± 1,790) remained fairly constant over the experimental period in each colony. However, the presence and amount of sealed drone brood was very variable. One colony had drone brood for 10 months and another for only 1 month. Both the mean infestation level of worker brood (18.1 ± 8.4%) and adult bees (3.5 ± 1.3%) remained fairly constant over the study period and did not increase rapidly as is normally observed in European honey bees. In fact, the estimated mean number of mites fell from 3,500 in February 1997 to 2,380 in January 1998. In May 2000 the mean mite population in the study colonies was still only 1,821 mites. The fertility level of mites in this study was much higher (83–96%) than in AHB in Brazil(25–57%), and similar to that found in EHB (76–94%). Mite fertility remained high throughout the entire study and was not influenced by the amount of pollen, honey or worker brood in the colonies. This revised version was published online in July 2006 with corrections to the Cover Date.     

The influence of brood comb cell size on the reproductive behavior of the ectoparasitic mite Varroa destructor in Africanized honey bee colonies

Africanized honey bees (Apis mellifera, Hymenoptera: Apidae) in Brazil are tolerant of infestations with the exotic ectoparasitic mite, Varroa destructor (Mesostigmata: Varroidae), while the European honey bees used in apiculture throughout most of the world are severely affected. Africanized honey bees are normally kept in hives with both naturally built small width brood cells and with brood cells made from European-sized foundation, yet we know that comb cell size has an effect on varroa reproductive behavior. Three types (sizes) of brood combs were placed in each of six Africanized honey bee colonies: new (self-built) Africanized comb, new Italian comb (that the bees made from Italian-sized commercial foundation), and new Carniolan comb (built naturally by Carniolan bees). About 100 cells of each type were analyzed in each colony. The Africanized comb cells were significantly smaller in (inner) width (4.84 mm) than the European-sized comb cells (5.16 and 5.27 mm for Italian and Carniolan cells, respectively). The brood cell infestation rates (percentage cells infested) were significantly higher in the Carniolan-sized comb cells (19.3%) than in the Italian and Africanized cells (13.9 and 10.3%, respectively). The Carniolan-sized cells also had a significantly larger number of invading adult female mites per 100 brood cells (24.4) than did the Italian-sized cells (17.7) and the natural-sized Africanized worker brood cells (15.6). European-sized worker brood cells were always more infested than the Africanized worker brood cells in the same colony. There was a highly significant correlation (P<0.01) between cell width and the rate of infestation with varroa in four of the six colonies. The small width comb cells produced by Africanized honey bees may have a role in the ability of these bees to tolerate infestations by Varroa destructor, furthermore it appears that natural-sized comb cells are superior to over-sized comb cells for disease resistance.     

Behavioral rhythmicity, age, division of labor and period expression in the honey bee brain.

Young adult honey bees work inside the beehive "nursing" brood around the clock with no circadian rhythms; older bees forage for nectar and pollen outside with strong circadian rhythms. Previous research has shown that the development of an endogenous rhythm of activity is also seen in the laboratory in a constant environment. Newly emerging bees maintained in isolation are typically arrhythmic during the first few days of adult life and develop strong circadian rhythms by about a few days of age. In addition, average daily levels of period (per) mRNA in the brain are higher in foragers or forager-age bees (> 21 days of age) relative to young nest bees (approximately 7 days of age). The authors used social manipulations to uncouple behavioral rhythmicity, age, and task to determine the relationship between these factors and per. There was no obligate link between average daily levels of per brain mRNA and either behavioral rhythmicity or age. There also were no differences in per brain mRNA levels between nurse bees and foragers in social environments that promote precocious or reversed behavioral development. Nurses and other hive-age bees can have high or low levels of per mRNA levels in the brain, depending on the social environment, while foragers and foraging-age bees always have high levels. These findings suggest a link between honey bee foraging behavior and per up-regulation. Results also suggest task-related differences in the amplitude of per mRNA oscillation in the brain, with foragers having larger diurnal fluctuation in per than nurses, regardless of age. Taken together, these results suggest that social factors may exert potent influences on the regulation of clock genes.     

How brood influences caste aggregation patterns in the dimorphic ant species Pheidole pallidula

Spatial distribution of ant workers and, notably their aggregation/segregation behaviour, is a key-element of the colony social organization contributing to the efficiency of task performance and division of labour. In polymorphic species, specialized worker castes notably differ in their intrinsic aggregation behaviour. In this context, knowing the preponderant role of minors in brood care, we investigate how a stimulus such as brood can influence the spatial patterns of Pheidole pallidula worker castes. In a homogeneous area without brood, it was shown that minors display only a low level of aggregation while majors form large clusters in the central area. Here we find out that these aggregation patterns of both minors and majors can be deeply influenced by the presence of brood. For minors, it nucleates or enhances the formation of a large stable cluster. Such high sensitivity of minors to brood stimuli fits well with their role as main brood tenders in the colony. For majors, interattraction between individuals still remains the prevailing aggregation factor while brood strongly influences the localisation of their cluster. We discuss how the balance between interattraction and sensitivity to environmental stimuli determines the mobility of each worker castes and, consequently, the availability of minors and majors to participate in everyday colony tasks. Moreover, we will evoke the functional value of majors’ cluster location close to the brood, namely with respect to social regulation of the colony caste ratio. Received 30 May 2005; revised 11 January 2006; accepted 13 January 2006.     

ORIGINS,EVOLUTION, AND DIVERSIFICATION OF CLEPTOPARASITIC LINEAGES IN LONG‐TONGUED BEES

The evolution of parasitic behavior may catalyze the exploitation of new ecological niches yet also binds the fate of a parasite to that of its host. It is thus not clear whether evolutionary transitions from free‐living organism to parasite lead to increased or decreased rates of diversification. We explore the evolution of brood parasitism in long‐tongued bees and find decreased rates of diversification in eight of 10 brood parasitic clades. We propose a pathway for the evolution of brood parasitic strategy and find that a strategy in which a closed host nest cell is parasitized and the host offspring is killed by the adult parasite represents an obligate first step in the appearance of a brood parasitic lineage; this ultimately evolves into a strategy in which an open host cell is parasitized and the host offspring is killed by a specialized larval instar. The transition to parasitizing open nest cells expanded the range of potential hosts for brood parasitic bees and played a fundamental role in the patterns of diversification seen in brood parasitic clades. We address the prevalence of brood parasitic lineages in certain families of bees and examine the evolution of brood parasitism in other groups of organisms.     

Maternity-related plasticity in circadian rhythms of bumble-bee queens

Unlike most animals studied so far in which the activity with no circadian rhythms is pathological or linked to deteriorating performance, worker bees and ants naturally care for their sibling brood around the clock with no apparent ill effects. Here, we tested whether bumble-bee queens that care alone for their first batch of offspring are also capable of a similar chronobiological plasticity. We monitored locomotor activity of Bombus terrestris queens at various life cycle stages, and queens for which we manipulated the presence of brood or removed the ovaries. We found that gynes typically emerged from the pupae with no circadian rhythms, but after several days showed robust rhythms that were not affected by mating or diapauses. Colony-founding queens with brood showed attenuated circadian rhythms, irrespective of the presence of ovaries. By contrast, queens that lost their brood switched again to activity with strong circadian rhythms. The discovery that circadian rhythms in bumble-bee queens are regulated by the life cycle and the presence of brood suggests that plasticity in the circadian clock of bees is ancient and related to maternal behaviour or physiology, and is not a derived trait that evolved with the evolution of the worker caste.     

Nestmate recognition in the stingless bee Melipona panamica (Apidae, Meliponini)

Summary: Nestmate recognition was studied in the Neotropical stingless bee Melipona panamica, a species in which workers "sneak" their own reproductive eggs into 1 % of brood cells. We manipulated four factors that could influence individual recognition cues: the mother queen, the environment during the immature stage, the environment during the early adult stage, and worker age. We also simulated the action of natural enemies on colonies tested for discrimination of such worker characteristics. All factors that we tested affected responses of the discriminating workers, which could recognize sisters, nieces and unrelated workers. Previous exposure of unrelated callow bees to the odor of the host nest greatly increased chances of acceptance by the host colony. Probability of acceptance decreased, however, with increasing age of introduced bees or increasing disturbance of the host colony. These complexities in patterns of nestmate recognition and nest defense are adequately explained from the standpoint of inclusive fitness of the discriminating workers. Differences in nestmate recognition and worker egg laying among Meliponini are also discussed.     

Honey bees (Apis mellifera) reared in brood combs containing high levels of pesticide residues exhibit increased susceptibility to Nosema (Microsporidia) infection

Nosema ceranae and pesticide exposure can contribute to honey bee health decline. Bees reared from brood comb containing high or low levels of pesticide residues were placed in two common colony environments. One colony was inoculated weekly with N. ceranae spores in sugar syrup and the other colony received sugar syrup only. Worker honey bees were sampled weekly from the treatment and control colonies and analyzed for Nosema spore levels. Regardless of the colony environment (spores+syrup added or syrup only added), a higher proportion of bees reared from the high pesticide residue brood comb became infected with N. ceranae, and at a younger age, compared to those reared in low residue brood combs. These data suggest that developmental exposure to pesticides in brood comb increases the susceptibility of bees to N. ceranae infection.     

Varroa-tolerant Italian honey bees introduced from Brazil were not more efficient in defending themselves against the mite Varroa destructor than Carniolan bees in Germany

In Europe and North America honey bees cannot be kept without chemical treatments against Varroa destructor. Nevertheless, in Brazil an isolated population of Italian honey bees has been kept on an island since 1984 without treatment against this mite. The infestation rates in these colonies have decreased over the years. We looked for possible varroa-tolerance factors in six Italian honey bee colonies prepared with queens from this Brazilian island population, compared to six Carniolan colonies, both tested at the same site in Germany. One such factor was the percentage of damaged mites in the colony debris, which has been reported as an indicator of colony tolerance to varroa. A mean of 35.8% of the varroa mites collected from the bottoms of the Italian bee colonies were found damaged, among which 19.1% were still alive. A significantly greater proportion of damaged mites were found in the Carniolan bees (42.3%) and 22.5% were collected alive. The most frequent kind of damage found was damaged legs alone, affecting 47.4% of the mites collected from debris in Italian bees, which was similar to the amount found in Carniolan colonies (46%). The mean infestation rate by the varroa mite in the worker brood cells in the Italian bee colonies was 3.9% in June and 3.5% in July, and in drone brood cells it was 19.3% in June. In the Carniolan honey bee colonies the mean infestation rates in worker brood cells were 3.0 and 6.7%, respectively in the months of June and July and 19.7% in drone brood cells in June. In conclusion, the 'Varroa-tolerant' Italian honey bees introduced from Brazil produced lower percentages of damaged mites (Varroa destructor) in hive debris and had similar brood infestation rates when compared to 'susceptible' Carniolan bees in Germany. In spite of the apparent adaptation of this population of Italian bees in Brazil, we found no indication of superiority of these bees when we examined the proportions of damaged mites and the varroa-infestation rates, compared to Carniloan bees kept in the same apiary in Germany.     

Task-specific expression of the foraging gene in harvester ants

In social insects, groups of workers perform various tasks such as brood care and foraging. Transitions in workers from one task to another are important in the organization and ecological success of colonies. Regulation of genetic pathways can lead to plasticity in social insect task behaviour. The colony organization of advanced eusocial insects evolved independently in ants, bees, and wasps and it is not known whether the genetic mechanisms that influence behavioural plasticity are conserved across species. Here we show that a gene associated with foraging behaviour is conserved across social insect species, but the expression patterns of this gene are not. We cloned the red harvester ant (Pogonomyrmex barbatus) ortholog (Pbfor) to foraging, one of few genes implicated in social organization, and found that foraging behaviour in harvester ants is associated with the expression of this gene; young (callow) worker brains have significantly higher levels of Pbfor mRNA than foragers. Levels of Pbfor mRNA in other worker task groups vary among harvester ant colonies. However, foragers always have the lowest expression levels compared to other task groups. The association between foraging behaviour and the foraging gene is conserved across social insects but ants and bees have an inverse relationship between foraging expression and behaviour.