Variation in colony structure in the subterranean termite Reticulitermes flavipes

The genetic organization of colonies of the subterranean termite Reticulitermes flavipes in two subpopulations in Massachusetts was explored using five polymorphic allozymes and double-strand conformation polymorphism (DSCP) analysis of the mitochondrial control region. Empirically obtained estimates of worker relatedness and F-statistics were compared with values generated by computer simulations of breeding schemes to make inferences about colony organization. In one study site (G), worker genotypes indicated the presence of a mixture of colonies headed by monogamous outbred primary reproductives and colonies headed by inbreeding neotenic reproductives, both colony types having limited spatial ranges. A second site (S) was dominated by several large colonies with low relatedness among nestmates. Mixed DSCP haplotypes in three colonies indicated that nestmates had descended from two or three unrelated female reproductives. Computer simulations of breeding schemes suggested that positive colony inbreeding coefficients at site S resulted from either commingling of workers from different nests or different colonies. Such an exchange of workers between nests corresponds to the multiple-site nesting lifetype of many subterranean termites and resembles colony structure in polycalic Formica ants. Our study demonstrates considerable variation in R. flavipes colony structure over a small spatial scale, including colonies headed by monogamous outbred primary reproductives, colonies containing multiple inbred neotenic reproductives and large polydomous colonies containing the progeny of two or more unrelated queens, and suggests that the number of reproductives and nestmate relatedness change with colony age and size.     

Caste determination and differential diapause within the first brood of Halictus rubicundus in New York (Hymenoptera: Halictidae)

Summary The partially bivoltine, primitively eusocial sweat bee Halictus rubicundus produces two female castes, gynes and non-gynes, in its first brood in New York. Castes in this brood differentiate within the first few days of adult life, with gynes leaving the population to overwinter as early as mid-June (non-gynes further differentiate into replacement queen and worker subcastes, with older females typically dominant). Analysis of possible mechanisms of caste determination reveals that although gynes average significantly larger than non-gynes within the first brood, this appears largely due to a late mean emergence data coupled with an increase in the size of emerging females over the course of brood emergence, rather than a causal relationship. A strong correspondence between male abundance (relative to newly-emerged females) and the pattern of gyne production, along with data from dissections, suggests that females that mate when young become diapausing gynes, while those that do not mate promptly become non-gynes and do not diapause even though many mate later. Although alternatives to this simple mechanism cannot be ruled out entirely, it nevertheless offers profound implications for theoretical and empirical understanding of the evolutionary origins of the worker caste.     

A genetic component to size in queens of the ant,<Emphasis Type="Italic"> Formica truncorum</Emphasis>

The genetic basis of morphological traits in social insects remains largely unexplored. This is even true for individual body size, a key life-history trait. In the social insects, the size of reproductive individuals affects dispersal decisions, so that small size in queens is often associated with reduced dispersal, and large size with long-range dispersal and independent colony founding. Worker size is connected to division of labour when workers specialize in certain tasks according to their size. In many species, variation in worker size has been shown to increase colony performance. In this study, we present the first evidence of an additive genetic component to queen size in ants, using maternal half sib analysis. We also compared intra-colony size variation in colonies with high (queen doubly mated) versus low (queen singly mated) genetic variability. We found a high and significant heritability (h²=0.51) for queen size in one of the two study years, but not in the other. Size variation among queens was greater in colonies headed by a doubly mated queen in one of the study years, but not in the other. This indicates that genetic factors can influence queen size, but that environmental factors may override these under some circumstances. The heritability for worker size was low (h²=0.09) and non-significant. Increased genetic diversity did not increase worker size variation in the colonies. Worker size appeared largely environmentally determined, potentially allowing colonies to adjust worker size ratios to current conditions.Communicated by J. Heinze     

Division of labour and worker size polymorphism in ant colonies: the impact of social and genetic factors

Division of labour among workers is central to the organisation and ecological success of insect societies. If there is a genetic component to worker size, morphology or task preference, an increase in colony genetic diversity arising from the presence of multiple breeders per colony might improve division of labour. We studied the genetic basis of worker size and task preference in Formica selysi, an ant species that shows natural variation in the number of mates per queen and the number of queens per colony. Worker size had a heritable component in colonies headed by a doubly mated queen (h ²=0.26) and differed significantly among matrilines in multiple-queen colonies. However, higher levels of genetic diversity did not result in more polymorphic workers across single- or multiple-queen colonies. In addition, workers from multiple-queen colonies were consistently smaller and less polymorphic than workers from single-queen colonies. The relationship between task, body size and genetic lineage appeared to be complex. Foragers were significantly larger than brood-tenders, which may provide energetic or ergonomic advantages to the colony. Task specialisation was also often associated with genetic lineage. However, genetic lineage and body size were often correlated with task independently of each other, suggesting that the allocation of workers to tasks is modulated by multiple factors. Overall, these results indicate that an increase in colony genetic diversity does not increase worker size polymorphism but might improve colony homeostasis.     

Resource supplements cause a change in colony sex-ratio specialization in the mound-building ant, Formica exsecta

We examine the role of food resources on split sex ratios in Formica exsecta. Models of resource-based sex allocation predict that greater resources will cause an increase in the production of reproductive females (gynes) and an increase in overall size of offspring. We experimentally increased food resources for a subset of colonies in a polygynous population with a very male-biased sex ratio. This increase in food availability caused colonies that were male specialists the prior year to switch to female production. Overall, a significantly greater proportion of food-supplemented colonies produced gynes, compared to control colonies. Moreover, food-supplemented colonies produced significantly larger workers and males (but not gynes), compared to those produced by control colonies. There was, however, no significant difference in the numerical productivity of food-supplemented and control colonies. We also measured the natural association between colony sex specialization and proximity to conifers, which typically harbor honeydew-bearing aphids (an important natural food source). In line with the view that resources play an important role for determining sex ratios in social insects, we found that female-producing colonies were significantly closer to conifers than were male-producing colonies.     

Sex ratio determination and worker reproduction in the slave-making ant Harpagoxenus sublaevis

Summary In a population of the monogynous slave-making ant Harpagoxenus sublaevis in S.E. Sweden, the mean proportion of dry weight investment in queens was 0.54. This result differed significantly from 0.75 but not from 0.5, matching the prediction from the genetic relatedness hypothesis of sex ratio applied to slave-makers, given (as confirmed by this study) single mating of queens, population-wide mate competition, and relatively low levels of worker male production. Sex investment appeared unaffected by resource availability. In the same 47 colony population sample, fertile slave-maker workers were found in every queenless colony (ca. 30% of all colonies), and in 58% of queen-right colonies. Fertile workers occurred at a significantly higher frequency in the queenless colonies (19.2%) than in the queenright ones (9.8%), confirming that queenless conditions promote worker fertility. Fertile and sterile workers were similar in size. Electrophoretic allozyme analysis of ants from 49 colonies showed that: 1) queens mated singly; 2) female nestmates were full sisters (their regression coefficient of relatedness (±SE) was 0.735±0.044); 3) inbreeding did not occur; 4) queen and worker siblings were not genetically differentiated. Worker male production in queenright colonies was neither confirmed nor ruled out by the genetic data. However, production data indicated that queenless workers produced between 4.4 and 21.6% of all males. Overall colony productivity was largely determined by slave number, itself positively correlated with the number of slave-maker workers. There was an abrupt switch from all worker to all sexual production as colony size rose, as predicted by life history models. In queenright colonies, fertile slave-makers did not discernibly reduce colony productivity. Such workers occurred in queenright colonies with most slaves, suggesting they exploited energetic surpluses. Worker reproduction in H. sublaevis therefore appears to have greater influence at the level of individual behaviour than at colony or population level.     

Social influences on body size and developmental time in the bumblebee Bombus terrestris

In many social insects, including bumblebees, the division of labor between workers relates to body size, but little is known about the factors influencing larval development and final size. We confirmed and extend the evidence that in the bumblebee Bombus terrestris the adult bee body size is positively correlated with colony age. We next performed cross-fostering experiments in which eggs were switched between incipient (before worker emergence) and later stage colonies with workers. The introduced eggs developed into adults similar in size to their unrelated nestmates and not to their same-age full sisters developing in their mother colony. Detailed observations revealed that brood tending by the queen decreases, but does not cease, in young colonies with workers. We next showed that both worker number and the queen presence influenced the final size of the developing brood, but only the queen influence was mediated by shortening developmental time. In colonies separated by a queen excluder, brood developmental time was shorter in the queenright compartment. These findings suggest that differences in body size are regulated by the brood interactions with the queen and workers, and not by factors inside the eggs that could vary along with colony development. Finally, we developed a model showing that the typical increase in worker number and the decrease in brood contact with the queen can account for the typical increase in body size. Similar self-organized social regulation of brood development may contribute to the optimization of growth and reproduction in additional social insects.     

Incest avoidance,fluctuating asymmetry,and the consequences of inbreeding in Iridomyrmex humilis,an ant with multiple queen colonies

Summary Inbreeding may have important consequences for the genetic structure of social insects and thus for sex ratios and the evolution of sociality and multiple queen (polygynous) colonies. The influence of kinship on mating preferences was investigated in a polygynous ant species, Iridomyrmex humilis, which has within-nest mating. When females were presented simultaneously with a brother that had been reared in the same colony until the pupal stage and an unrelated male produced in another colony, females mated preferentially with the unrelated male. The role of environmental colony-derived cues was tested in a second experiment where females were presented with two unrelated males, one of which had been reared in the same colony until the pupal stage (i.e., as in the previous experiment), while the other had been produced in another colony. In this experiment there was no preferential mating with familiar or unfamiliar males, suggesting that colony-derived cues might not be important in mating preferences. Inbreeding was shown to have no strong effect on the reproductive output of queens as measured by the number of worker and sexual pupae produced. The level of fluctuating asymmetry of workers produced by inbreeding queens was not significantly higher than that of non-inbreeding queens. Finally, colonies headed by inbreeding queens did not produce adult diploid males. Based on the current hypotheses of sex-determination the most plausible explanations for the absence of diploid-male-producing colonies are that (i) workers recognized and eliminated these males early in their development, and/or (ii) there are multiple sex-determining loci in this species. It is suggested that even if inbreeding effects on colony productivity are absent or low, incest avoidance mechanisms may have evolved and been maintained if inbreeding queens produce a higher proportion of unviable offspring. Correspondence to: L. Keller at the present address     

Reproductive decision-making in semelparous colonies of the bumblebee bombus terrestris

Queen and worker Bombus terrestris have different optima for the timing of gyne production. Workers, being more related to their gyne-sisters than to their sons, should ascertain that gyne production has started before attempting to reproduce. Their optimal timing for gyne production will be as early as possible, while allowing sufficient ergonomic colony growth to support gyne rearing. Queen optimum, on the other hand, should be to postpone gyne production toward the end of colony life cycle, in order to minimize the time-window available for worker reproduction. Thus, the timing of gyne production may profoundly affect the outcome of queen–worker competition over male production. In this study we investigated some of the social correlates possibly affecting this timing. It was found that neither keeping colony size constant and as low as 20 workers, nor decreasing worker average age, influenced the onset of gyne production. To test the effect of queen age we created young colonies with old queens and vice versa. When colony social composition remained unchanged, in young colonies headed by old queens gynes were produced earlier than predicted, but in the inverse situation gyne production was not delayed. When colony social composition was completely standardized queen age had a decisive effect, indicating that the timing of gyne production is both under queen influence and affected by queen age. Furthermore, queens assess colony age from the time of first worker emergence rather than from their own first oviposition. In these experiments the factors affecting gyne production also affected the onset of queen–worker conflict for male production, suggesting that both are regulated by the same causal effect. Postponing gyne production as much as possible provides another mechanism, in addition to extensive oophagy, for the queen to outcompete her workers in male production.     

Multiple paternity and colony homeostasis in<Emphasis Type="Italic"> Lasius niger</Emphasis> ants

Multiple mating by social insect queens is a common phenomenon despite likely imposing substantial costs on queens. Mating with several males could be adaptive if a more genetically diverse worker force is better able to always handle any task sufficiently well, leading to a higher colony homeostasis. If multiple-paternity colonies are more homeostatic, then I propose that they may constitute less stressful rearing environments for developing sexuals. The effective stress levels experienced by developing males and queens may, however, also depend on colony productivity and sex-ratio preferences. I tested these hypotheses in the ant Lasius niger by examining whether the fluctuating asymmetry, means and coefficients of variation of a set of phenotypic traits in males and new queens co-varied with the effective number of patrilines per colony, colony productivity or sex ratio.Little support was found that the level of intra-colonial genetic diversity affects the variation of phenotype in sexuals. In 1 out of 2 years, however, females from colonies with high effective patriline numbers were heavier relative to their head width than were females from colonies with few patrilines. Support was found for the hypothesis that colonies with more resources may invest more in individual sexuals, and tendencies suggested that sexuals may receive better treatment when they belong to the majority sex of their colony.Communicated by J. Heinze     

Foundress polyphenism and the origins of eusociality in a facultatively eusocial sweat bee, Megalopta genalis (Halictidae)

The reproductive (queen) and nonreproductive (worker) castes of eusocial insect colonies are a classic example of insect polyphenism. A complementary polyphenism may also exist entirely among females in the reproductive caste. Although less studied, reproductive females may vary in behavior based on size-associated attributes leading to the production of daughter workers. We studied a bee with flexible social behavior, Megalopta genalis, to better understand the potential of this polyphenism to shape the social organization of bee colonies and, by extension, its role in the evolution of eusociality. Our experimental design reduced variation among nest foundresses in life history variables that could influence reproductive decisions, such as nesting quality and early adulthood experience. Within our study population, approximately one third of M. genalis nests were eusocial and the remaining nests never produced workers. Though they do not differ in survival, nest-founding females who do not attempt to produce workers (which we refer to as the solitary phenotype) are significantly smaller and become reproductive later than females who attempt to recruit workers (the social phenotype). Females with the social phenotype are more likely to produce additional broods but at a cost of having some of their first offspring become nonreproductive workers. The likelihood of eusocial organization varies with body size across females of the social phenotype. Thus, fitness consequences associated with size-based plasticity in foundress behavior has colony level effects on eusociality. The potential for size-based polyphenisms among reproductive females may be an important factor to consider in the evolutionary origins of eusociality.     

Individual responsiveness to shock and colony-level aggression in honey bees: evidence for a genetic component

The phenotype of the social group is related to phenotypes of individuals that form that society. We examined how honey bee colony aggressiveness relates to individual response of male drones and foraging workers. Although the natural focus in colony aggression has been on the worker caste, the sterile females engaged in colony maintenance and defense, males carry the same genes. We measured aggressiveness scores of colonies and examined components of individual aggressive behavior in workers and haploid sons of workers from the same colony. We describe for the first time, that males, although they have no stinger, do bend their abdomen (abdominal flexion) in a posture similar to stinging behavior of workers in response to electric shock. Individual worker sting response and movement rates in response to shock were significantly correlated with colony scores. In the case of drones, sons of workers from the same colonies, abdominal flexion significantly correlated but their movement rates did not correlate with colony aggressiveness. Furthermore, the number of workers responding at increasing levels of voltage exhibits a threshold-like response, whereas the drones respond in increasing proportion to shock. We conclude that there are common and caste-specific components to aggressive behavior in honey bees. We discuss implications of these results on social and behavioral regulation and genetics of aggressive response.     

The metabolic costs of building ant colonies from variably sized subunits

Ant colonies are superorganisms with emergent traits that, for some species, reflect the combined activity of physically distinct worker castes. Although larger castes have high production costs, they are thought to save their colonies energy by efficiently performing specialized tasks. However, because workers are generally idle until sensing specific stimuli, their maintenance costs may be an important component of colony-level investment. I used metabolic scaling to examine the maintenance costs of dimorphic major and minor Pheidole castes across levels of colony organization (e.g., individual, group, and colony). Majors from three species had lower mass-specific metabolic rates than minors because of allometries at both individual and group levels and subsequently lived longer when starved. Thus, large major castes may offset their production costs in both their idle and active states. The slope scaling metabolic rate from incipient to reproductive colonies of Pheidole dentata (∼colony mass^0.89) fell between the slopes for minor groups (∼group mass^1.04) and major groups (∼group mass^0.79) and appears to reflect developmental shifts in subunit mass and number and their offsetting effects on per capita energy demands. These results highlight how metabolic scaling may help visualize the energetic correlates of emergent behavior and unravel the mechanisms governing colony organization.     

Production of sexuals in a fission-performing ant: dual effects of queen pheromones and colony size

Models based on the kin selection theory predict that in social hymenopterans, queens may favor a lower investment in the production of sexuals than workers. However, in perennial colonies, this conflict may be tuned down by colony-level selection because of the trade off between colony survival and reproductive allocation. In this study, we present a survey of sexual production in colonies of Aphaenogaster senilis, a common species of ant in the Iberian Peninsula. Similar to most species that reproduce by fission, males were found in large excess compared to gynes (172:1). Sexuals were more likely to be found in queenless than in queenright (QR) field colonies. However, we also found a few gynes and numerous males in very large QR colonies. We compared these data with those available in the literature for A. rudis, a congeneric species from North America that has independent colony founding. The sex ratio in this species was only five males for each female, and sexuals were mostly found in QR nests, irrespective of colony size. We confirmed queen inhibition of sexual production in A. senilis in laboratory experiments and provide evidence that this inhibition is mediated by a nonvolatile pheromone. To seek the potential source of such a queen pheromone, we analyzed the secretions of two conspicuous exocrine glands, the Dufour’s and postpharyngeal glands (DG and PPG, respectively) in both queens and workers. Both secretions were composed of hydrocarbons, but that of DG also contained small quantities of tetradecanal and hexadecanal. The hydrocarbon profile of the DG and PPG showed notable caste specificity suggesting a role in caste-related behavior. The PPG secretions also differed between colonies suggesting its role in colony-level recognition. We suggest that in A. senilis, there are two modes of colony fission: First, in very large colonies, gynes are produced, probably because of the dilution of the queen pheromone, and consequently one or more gynes leave the mother colony with workers and brood to found a new nest. This is beneficial at the colony level because it avoids the production of costly sexuals in small colonies. However, because the queen and workers have different optima for sexual production, we hypothesize that queens tend to overproduce the pheromone to delay their production. This in turn may drive workers to leave the mother colony during nest relocation and to produce sexuals once they are away from the queen’s influence, creating a second mode of colony fission.     

Support for maternal manipulation of developmental nutrition in a facultatively eusocial bee, <Emphasis Type="Italic">Megalopta genalis</Emphasis> (Halictidae)

Developmental maternal effects are a potentially important source of phenotypic variation, but they can be difficult to distinguish from other environmental factors. This is an important distinction within the context of social evolution, because if variation in offspring helping behavior is due to maternal manipulation, social selection may act on maternal phenotypes, as well as those of offspring. Factors correlated with social castes have been linked to variation in developmental nutrition, which might provide opportunity for females to manipulate the social behavior of their offspring. Megalopta genalis is a mass-provisioning facultatively eusocial sweat bee for which production of males and females in social and solitary nests is concurrent and asynchronous. Female offspring may become either gynes (reproductive dispersers) or workers (non-reproductive helpers). We predicted that if maternal manipulation plays a role in M. genalis caste determination, investment in daughters should vary more than for sons. The mass and protein content of pollen stores provided to female offspring varied significantly more than those of males, but volume and sugar content did not. Sugar content varied more among female eggs in social nests than in solitary nests. Provisions were larger, with higher nutrient content, for female eggs and in social nests. Adult females and males show different patterns of allometry, and their investment ratio ranged from 1.23 to 1.69. Adult body weight varied more for females than males, possibly reflecting increased variation in maternal investment in female offspring. These differences are consistent with a role for maternal manipulation in the social plasticity observed in M. genalis.     

The biology of a subtropical population of Halictus ligatus Say (Hymenoptera: Halictidae)

Summary A large population of Halictus ligatus was studied in the subtropical climate of Knights Key, Monroe County, Florida. The dissection of 858 female bees caught on flowers and 420 bees from completely excavated nests gives the following picture of phenology, colony development and social organisation. In the Florida keys, H. ligatus is continuously brooded and multivoltine. However, towards the coldest time of year young gynes may rest in their natal nests rather than found a new colony. This may result in a partial synchronisation of nest initiation when warm weather returns after a particularly cold spell. Most nests are started by a single foundress that usually survives until near the end of the production of reproductives. The first brood is very variable in size and males average 11% of the bees produced at this stage. This figure increases to 56% when the first brood workers begin provisioning. Queens are produced some time after the rise in male production and colony longevity is extended by the presence of some worker brood during this phase. Queens average 16% larger than their workers but appear to exert little inhibition of worker reproductivity: 57% of worker bees mate and 68% show ovarian development. This population is unique amongst social halictines in being continuously brooded, multivoltine and in having such weak physiological caste differentiation. It seems to represent an intermediate stage between the primitively eusocial colonies of H. ligatus found in temperate regions and the communal-like ones of the tropics.     

Origin of male-biased sex allocation in orphaned colonies of the termite, <Emphasis Type="Italic">Coptotermes lacteus</Emphasis>

In eusocial insects, sex allocation often constitutes a ground for intracolonial conflicts. This occurrence provides ideal opportunities to test kin-selection theory. A vast literature on this topic is available for social Hymenoptera, but the same field remains almost untouched in termites. A preeminent case is that of some species of Coptotermes, where the sex-allocation ratio in nymphs shifts from near equity to all-male when the primary reproductives are replaced by neotenics. To shed light on the developmental origin of this shift, we compared the sex ratio of the various castes and instars in primary- and neotenic-headed mature colonies of Coptotermes lacteus. The male-biased sex allocation in the latter type of colony results from two concurrent events: first, the sex ratio of the youngest instars (larvae) is male-biased by a 3:1 ratio; and second, all female larvae become workers, while a large fraction of the male larvae proceed to the nymphal and alate stages. Colony-founding experiments showed that inbreeding by itself cannot account for the male bias at hatching. We suggest that both genetic factors, due to the reproductive behaviour of neotenics, and environmental factors (colony condition and resource availability) may influence this process. Their exact nature and respective impact have not yet been clarified.     

Queen dimorphism and reproductive strategies in the fire ant Solenopsis geminata (Hymenoptera: Formicidae)

Alate trapping studies of a monogyne population of the fire ant Solenopsis geminata indicate that two sizes of gynes are produced. Macrogynes, which participate in late spring and summer mating flights, are larger, fattier, and more than twice as heavy as microgynes, which participate in fall mating flights. Three patterns of gyne production were observed in 51 colonies studied: 35 produced macrogynes only, 9 produced microgynes only, and 7 produced both morphs, contributing to both summer and fall mating flights. Behavioral evidence and rearing studies suggest that macrogynes found new colonies independently, whereas microgynes achieve colony queen status by infiltrating or being adopted by established colonies. Of the total number of female alates collected from the trapped colonies, 56% were microgynes. However, because of their smaller size and lower fat content, microgynes made up only one-third of the caloric investment in female alates. By measuring the thorax lengths of queens from mature colonies, we determined that at least 56% were macrogynes and 35% or more were microgynes. These results indicate that as a reproductive strategy, colony investment in microgyne production may have at least as high a payoff as investment in macrogyne production.This is publication #24 of the Fire Ant Research Team     

Sex allocation ratios in the facultatively polygynous ant, Leptothorax acervorum

We investigated sex allocation in a central European population of the facultatively polygynous ant Leptothorax acervorum. The population-wide sex ratio was found to be quite balanced, with a proportional investment in female sexuals of 0.49. Sex allocation varied considerably between colonies, resulting in split sex ratios. The productivity of colonies was negatively correlated with queen number and positively with colony size. In contrast, the sex ratio (proportional investment in female sexuals) was neither correlated with queen number, colony size, nor total sexual production, but with worker relatedness. The uncoupling of the genetic colony structure and queen number presumably results from frequent queen turnover and colony splitting.     

Demography, demand, death, and the seasonal allocation of labor in the Florida harvester ant (Pogonomyrmex badius)

As a self-organizing entity, an ant colony must divide a limited number of workers among numerous competing functions. Adaptive patterns of labor allocation should vary with colony need across each annual cycle, but remain almost entirely undescribed in ants. Allocation to foraging in 55 field colonies of the Florida harvester ant (Pogonomyrmex badius) followed a consistent annual pattern over 4 years. Foragers preceded larvae in spring and peaked during maximal larval production in summer (0.37). In spring, proportion foraging increased due to an increase in forager number and reduction in colony size, and in late summer, it decreased as colony size increased through new worker birth and a loss of ～3 % of foragers per day. The removal of 50 % of the forager population revealed that, at the expense of larval survival, colonies did not draw workers from other castes to fill labor gaps. To determine if labor allocation was age specific, whole colonies were marked with cuticle color-specific wire belts and released, and each cohort's time to first foraging was noted. Workers that eclosed in summer alongside sexual alates darkened quickly and became foragers at ～43 days of age, whereas autumn-born workers required 200 or more days to do so. Following colony reproduction, these long-lived individuals foraged alongside short-lived, summer-born sisters during the next calendar year. Therefore, the large-scale, predictable patterns of labor allocation in P. badius appear to be driven by bimodal worker development rate and age structure, rather than worker responsiveness to changes in colony demand.