Social behavior of early emerging males of a Japanese paper wasp,Polistes chinensis antennalis (Hymenoptera: Vespidae)

Summary Five cases of the early emergence of males in a Japanese paper wasp,Polistes chinensis antennalis, in which male emerged together with the first group of workers, were described. In one case of the five where the queen disappeared before the emergence of male, worker(s) produced female offspring. The frequency of the nests where the early emergence of male was observed was 16.7% (5/30 nests). In two colonies, worker(s) and/or queen chased off males. But in an orphan nest where worker(s) produced female offspring, the dominance order among workers which was similar to that of colony without male was observed. The significance of the early emergence of male in the social evolution of wasps was discussed.     

Queen mating frequency and maternity of males in the stingless bee Trigona carbonaria Smith

Summary. Aspects of the sociobiology of the native Australian stingless bee Trigona carbonaria (Hymenoptera, Meliponini) were investigated using highly variable microsatellite markers. The queen mating frequency was estimated by examining genotypes of samples of workers from five colonies across three to five microsatellite loci. In each case, results were consistent with the workers being progeny of a queen mated with a single male. Microsatellite analysis of haploid males from two of the colonies suggested they predominantly arose from queen-laid eggs. As workers are more related to sons-of-workers than to sons-of-queens in monandrous colonies, this is somewhat surprising, and suggests that there may be colony-level costs associated with worker reproduction, or that queens are able to regulate worker reproduction via the ritualized cell provisioning and oviposition process. Males from another T. carbonaria colony were found to be diploid.     

The biology of the primitively eusocial Augochloropsis iris (Schrottky, 1902) (Hymenoptera, Halictidae)

Summary: This work investigated Augochloropsis iris, its annual colony cycle, brood size and survival rate, caste differentiation, and sex ratio, and is the first detailed account of a clearly eusocial species of this genus. The population studied is located in the Campos do Jordão State Park, São Paulo, Brazil. The annual colony cycle extends from August to March and consists of three phases of cell provisioning separated by two phases of inactivity, and followed by an emergence of future queens and males. Provisioning during the first phase is carried primarily out by solitary females. The daughters, after emerging from the cells, remain in the natal nests, carrying out foraging activities, while the mother engages in reproduction. New nests are initiated during each of the provisioning phases by solitary females, principally by females from the second-phase brood which, soon after emerging from the cells, leave their natal nests to found their own nests, which they provision during the third phase. The females resulting from the third-phase brood in general mate and excavate their own nests, in which they diapause, with provisioning delayed until the following August. On average, the queens are significantly larger (5%) than the workers. In general, the workers do not have developed ovaries, but all are mated. Kin selection can be accepted as the selective force responsible for worker behavior of A. iris in eusocial colonies when the queen has mated once and semisocial colonies if the queen mated only once. The percentage of males produced in the first, second and third broods and in the brood of new nests founded by solitary females active in the second and third phases was: 20.7%, 22.2%, 13.3% and 0.0% respectively. The resultant sex ratio of the third brood suggests that the third-phase workers of eusocial nests are at least in partial control of their colony's sex ratios, in cases where the queens mated only once.     

Are workers of Atta leafcutter ants capable of reproduction?

Summary. Workers of most eusocial Hymenoptera can produce sons after queen loss, which (posthumously) benefits the queen and increases worker inclusive fitness. However, the evolutionary loss of worker ovaries has occurred in several lineages, while workers in other taxa may be infertile despite having ovaries. Workers of Atta leafcutter ants only lay trophic eggs in queenright colonies. Although Atta colonies are commonly kept at universities, museums, and zoos, no reports of worker sons in orphaned colonies exist, suggesting that Atta workers are infertile. To explicitly test this, we created eleven orphaned laboratory nests of Atta cephalotes, A. sexdens, and A. colombica, and maintained them for 3–6 months after queen loss. Eight colonies did not produce any brood, but three nests produced 1–4 worker-derived male larvae and pupae. Microsatellite genotyping indicated that these were worker sons. However, all males were tiny (3.5–9 mm long) compared to normal queen sons (16 mm long), and would almost certainly be unable to mate. We also found reproductive eggs, but most of these had no yolk and were thus inviable. We conclude that Atta workers are not completely infertile, but that worker fertility is low compared to the sister genus Acromyrmex, where workers routinely produce normally-size males after queen loss in the laboratory. We hypothesize that worker reproduction in orphaned Atta field colonies is almost never successful because the last workers die before their sons can be raised to adulthood, but that the importance of worker-laid trophic eggs for queen feeding has precluded the evolutionary loss of worker ovaries. Received 17 January 2005; revised 12 September 2005; accepted 3 October 2005.     

Complex sociogenetic organization and reproductive skew in a primitively eusocial sweat bee,Lasioglossum malachurum,as revealed by microsatellites

The sweat bees (Family Halictidae) are a socially diverse taxon in which eusociality has arisen independently numerous times. The obligate, primitively eusocial Lasioglossum malachurum, distributed widely throughout Europe, has been considered the zenith of sociality within halictids. A single queen heads a colony of smaller daughter workers which, by mid-summer, produce new sexuals (males and gynes), of which only the mated gynes overwinter to found new colonies the following spring. We excavated successfully 18 nests during the worker- and gyne-producing phases of the colony cycle and analysed each nest's queen and either all workers or all gynes using highly variable microsatellite loci developed specifically for this species. Three important points arise from our analyses. First, queens are facultatively polyandrous (queen effective mating frequency: range 1-3, harmonic mean 1.13). Second, queens may head colonies containing unrelated individuals (n = 6 of 18 nests), most probably a consequence of colony usurpation during the early phase of the colony cycle before worker emergence. Third, nonqueen's workers may, but the queen's own workers do not, lay fertilized eggs in the presence of the queen that successfully develop into gynes, in agreement with so-called 'concession' models of reproductive skew.     

Hemolymph juvenile hormone titers in worker honey bees under normal and preswarming conditions

Swarming is an important mechanism by which honey bee, Apis mellifera L., colonies reproduce, yet very little is known about the physiological changes in workers that are preparing to swarm. In this study, we determined the endocrine status of worker honey bees in preswarming colonies and in normal (nonswarming) colonies. Juvenile hormone (JH) titers in worker bees were similar in both groups before queen cells were present, but they became significantly lower in preswarming colonies compared with normal colonies when queen cells occurred in preswarming colonies. The lower JH titers in the preswarming colonies suggest that behavioral development is delayed in these colonies, consistent with previous reports that preswarming colonies have reduced foraging activities. Understanding the endocrine status of bees preparing for swarming will help us to better understand the biology of swarming.     

Genetic structure of colonies and a male aggregation in the stingless bee Scaptotrigona postica,as revealed by microsatellite analysis

Summary: Stingless bee queens have for long been assumed to mate once on a nuptial flight, early in life. To evaluate critically monandry in one stingless bee, Scaptotrigona postica, worker offspring (adults or brood) were genetically analysed with microsatellite loci, five of which were developed specifically for the species. Marker loci were highly variable; unbiased estimates of heterozygosity were > 0.5. "Foreign" workers, either those having drifted from other colonies (circa 2%) or those of a replacement queen, were identified with the genetic markers and removed from further analysis. Worker genotypes were consistent with some queens having mated once and others having mated with up to six different males. Scaptotrigona postica queens are therefore facultatively polyandrous. Effective mating frequencies, m_e, were generally lower than the number of patrilines observed. Relatedness estimates of nestmates from individual colonies concurred with those derived from direct counts of the number of patrilines and their proportional representation. Putative genotypes of a colony's queen and her mates were deduced from those of her workers. Queens were generally not related to their mates. For one polyandrous queen, her six mates were related to each other, possibly because of numerically biased representation of males from different colonies at mating sites. However, males at an aggregation outside a colony came from numerous colonies.     

Social organization, reproductive behavior and ecology of Leptothorax acervorum (Hymenoptera, Formicidae) from the Sierra de Albarracin in central Spain

Summary: Leptothorax acervorum, an ant species with holarctic range, occurs in an isolated population in the Spanish Sierra de Albarracin. Dissection of dealate females and laboratory observations revealed that in contrast to other European populations, the colonies are monogynous, with one reproductive queen each and a variable number of virgin or mated dealate but not laying females. Most of the latter probably just hibernate in the mother nests, leaving them in the following spring, but a few remain there for longer time, without reproducing. Such colonies then are functionally monogynous. Alate females exhibit a stationary sexual calling, and mating behavior could be studied in the laboratory. Mated females return to the mother nest where they soon shed wings. When developing fertility before or after hibernation they are evicted from the nests; in nature they probably form daughter colonies. Patchy habitat and rough climatic conditions in the Sierra de Albarracin may be responsible for the particular reproductive behavior of L. acervorum in this area. The generally small size difference between queens and workers in the subgenus Leptothorax entails high costs of dispersal and colony foundation by single queens who have to forage for their first brood. Some kind of dependent colony foundation therefore is frequently met with in the subgenus. Notwithstanding the marked biological and a few slight morphological differences between central European L. acervorum and the Spanish population its taxonomic status as yet is unsettled. We refer to this population provisionally as "L. acervorum Albarracin".     

Attraction and Repellence of Workers by the Honeybee Queen (Apis mellifera L.)

The spatial distribution of worker honeybees in colonies of two African subspecies ( Apis mellifera capensis and Apis mellifera scutellata ), as well as their natural hybrids, was determined in five observation colonies, each containing one frame. The queens were allowed to roam freely throughout the hive during the initial phase of the experiment, and were observed on both sides of the frame in all colonies. In the second phase of the experiment the queen was caged on one side of the frame in three of the observation colonies, the other two colonies serving as controls. Queen caging significantly affected the distribution of worker bees, with more A. m. scutellata workers being attracted to the queen and more A. m. capensis worker bees being repelled by the presence of the queen. The hybrid workers were also repelled, but to a lesser extent. Queens thus not only attract workers to form a retinue or during swarming but also repel workers in the nest. Evasion of the reproductive suppression by the queen pheromones may be a typical behavior for workers with a high reproductive potential.     

Nutritional function of replete workers in the pharaoh's ant, Monomorium pharaonis (L.)

Summary: Queens of the pharaoh's ant Monomorium pharaonis (L.), like several other ant species, feed on larval secretions as their main nourishment and their fecundity is positively correlated with the number of large larvae present in the nest. The surplus of secretions produced by larvae is stored in a temporary caste of replete workers, which comprises young workers who remain in the nest and store liquid nourishment. Repletes are characterised by a conspicuously large gaster, caused by large amounts of liquid food stored in the crop, from which it may be regurgitated and distributed among colony members. In this study, repletes of pharaoh's ants were demonstrated to be functioning as buffers, smoothing fluctuations in availability of high quality food to the reproductive queens when larvae are scarce or missing, thus temporarily keeping up the egg production of queens.¶In undisturbed two-queen colonies with 20 large worker larvae and 30 workers (15 young and 15 old workers), approximately 10 repletes developed (one replete per two larvae). Development of older workers into repletes, when some or all repletes had been removed from the colonies, demonstrated that their temporal polyethism exhibits great plasticity in this trait.¶This study confirmed that, in pharaoh's ants, the regulation of fecundity depends not only on the food flow to the queen from larvae or from repletes but also on an unknown larval stimulus.¶The term crop repletes is suggested for replete workers which use their crop to store nourishment, as opposed to fat-body repletes, which store nourishment in their fat body.¶The presence of brood tending crop repletes in nests in several European ant species of Leptothorax, Myrmica, and Lasius, show that repletism is a common trait in ants, and that it may play an important role in regulation of nutrition in ant colonies, as demonstrated in Monomorium pharaonis.     

Colony structure and reproduction in the thelytokous parthenogenetic ant Platythyrea punctata (F. Smith) (Hymenoptera, Formicidae)

Summary: An important evolutionary characteristic of the formicine subfamily Ponerinae is the occurrence of various alternative reproductive tactics within single species. In Platythyrea punctata Smith, 1858, queens, gamergates and parthenogenetic workers co-occur in the same species. Morphological queens, both alate and dealate, were present in only 29 percent of the colonies collected in Florida, but absent from colonies collected in Barbados and Puerto Rico. One of the six queens which were dissected (three alate and three dealate) was found to be inseminated but not fertile. Instead, in most queenless colonies, a single uninseminated worker monopolized reproduction by means of thelytokous parthenogenesis, i.e., it produced female offspring from unfertilized eggs. A single mated, reproductive worker (gamergate) was found dominating reproduction in the presence of an inseminated alate queen in one of the Florida colonies. Thelytokous parthenogenesis was examined in artificial groups of virgin laboratory-reared workers, where one worker typically monopolized reproduction despite the presence of several individuals with elongated ovaries. In 16 colonies collected in Florida, a total of 66 individuals differed morphologically from queens and workers. Their thorax morphology varied from a worker-like to an almost queen-like structure. We refer to these individuals as "intercastes" (sensu Peeters, 1991a). The remarkable complexity of reproductive strategies renders P. punctata unique within ants.     

Clustered male production by workers in the stingless bee Melipona subnitida Ducke (Apidae, Meliponinae)

Summary: In stingless bees brood cells are sequentially filled with liquid larval food (mass-provisioning), upon which the queen lays an egg. Thereafter the cell is closed by a worker. This study showed that during these processes workers of Melipona subnitida regularly laid eggs that served as food for the queen. Occasionally cells were oviposited in and immediately closed by a worker. These cells always rendered males. Some of these reproductive workers were seen to lay a trophic egg as well. Cells which were exclusively oviposited in by the physogastric queen gave rise to workers and queens only. In one colony it could be verified that three workers alone, which differed in age by one day, laid 15 male-producing eggs within a period of two successive weeks. Among them the number of ovipositions was positively related to the order in which workers eclosed - the oldest worker laying most eggs - and inversely related to the number of times they closed cells oviposited in exclusively by the queen. Apparently the physogastric queen was not able to stop certain workers from reproducing. We therefore conclude that some workers in M. subnitida temporarily dominated their queens in egg-laying.     

Temporal dynamics of facultative social parasitism in bumble bees (Hymenoptera: Apidae)

Parasitical behaviour is thought to play an important, yet so far largely unknown role in the evolution and maintenance of insect sociality. In this study, the influence of interspecific, facultative social parasitism upon bumble bee, Bombus, nesting biology was explored. Queens of B. affinis were introduced into 38 various-sized laboratory colonies of B. terricola. Foreign queens were very successful at killing the resident queen and usurping pre-worker nests (77% wins), although usurpation success decreased to 30% in colonies that contained workers. In addition, B. affinis queens were unable to suppress ovarian development in B. terricola workers that emerged prior to nest usurpation, resulting in the eventual death or expulsion of the foreign queen. In contrast, ovarian development was supporessed in workers that eclosed in the presence of a foreign queen, and in workers that were less than 5 h old when confined in small experimental boxes with a B. affinis queen. Foreign queens that usurped a nest prior to worker emergence were assisted by B. terricola workers, and achieved similar reproductive success when compared to a cohort of 22 B. affinis queens that initiated their own nests in the laboratory. These results suggest that there are periods in the ontogeny of Bombus nest defence, recognition and dominance during which bees are sensitive to the effects of nest parasitism. In bumble bees, and in other social insects, individuals of some species may exploit these weaknesses for their own reproductive benefit.     

The comparative biology of two sympatric paper wasps, the native Polistes fuscatus and the invasive Polistes dominulus (Hymenoptera, Vespidae)

Summary: Polistes dominulus (Christ), an old world paper wasp, was introduced accidentally into the eastern coast of the United States in the late 1970s and has been rapidly spreading westward, displacing the native P. fuscatus (F.). The biology of naturally nesting P. fuscatus and P. dominulus was compared at a field site in Rochester, Michigan. The basic methodology consisted of simultaneously videotaping spatially proximate, matched single-foundress colonies of P. fuscatus and P. dominulus (13 matched sets, 176.8 h of videography). In addition, extensive surveys and censuses were taken of colonies to record colony productivity, dates of nest initiation and first worker emergence, usurpation and parasitism.¶There was no evidence that P. dominulus is negatively impacting P. fuscatus through direct, agonistic encounters. However, P. dominulus is 4-5 times more productive than P. fuscatus, suggesting that P. dominulus is replacing P. fuscatus via exploitative competition. P. dominulus appears to have a number of advantages over P. fuscatus, including earlier production of workers, higher per capita foraging rates by queens and workers, higher queen survivorship, and lack of conspecific pressures. Nest site and/or prey availability may be limiting factors in the competition between the two species.     

Breeding behaviour, relatedness and sex-investment ratios inLeptothorax tuberum Fabricius

The ant speciesLeptothorax tuberum was shown to be predominantly monogynous. Queens usually mate once only but some nests may have a multiply-mated queen or are partially or serially polygynous. As expected from these results, within nest relatedness between workers and between workers and alate queens was found to be high. Almost fifty percent of nests had no nest queen which may indicate high queen mortality, queens leaving to found new nests or nest fragmentation. Observed female investment frequencies (IF _o ) were not significantly different from those expected on the basis of worker control of sexual production and the relatedness estimates of workers to alate queens and workers to males calculated from isozyme data (IF _E ). These values were not consistent with queen control. There was no evidence for lower IF _o s in queenless nests nor for higher IF _o s in larger nests classified by worker number. When nests were classified by sexual productivity, however, there was a strong rank correlation between productivity and female bias. This is the first study of an ant species to test observed IF against expected IF calculated without inferring between caste relatedness from worker data or pooling of data from different castes.     

Colony stage and not facultative policing explains pattern of worker reproduction in the Saxon wasp

Inclusive fitness theory predicts that in colonies of social Hymenoptera headed by a multiple‐mated queen, workers should benefit from policing eggs laid by other workers. Foster & Ratnieks provided evidence that in the vespine wasp Dolichovespula saxonica, workers police other workers’ eggs only in colonies headed by a multiple‐mated queen, but not in those headed by a single‐mated one. This conclusion, however, was based on a relatively small sample size, and the original study did not control for possible confounding variables such as the seasonal colony progression of the nests. Our aim, therefore, was to reinvestigate whether or not facultative worker policing occurs in D. saxonica. Remarkably, our data show that in the studied Danish population, there was no correlation between worker–worker relatedness and the percentage of worker‐derived males. In addition, we show that variability in cuticular hydrocarbon profiles among the workers did not significantly correlate with relatedness and that workers therefore probably did not have sufficient information on queen mating frequency from the workers’ cuticular hydrocarbon profiles. Hence, there was no evidence that workers facultatively policed other workers’ eggs in response to queen mating frequency. Nevertheless, our data do show that the seasonal progression of the nest and the location in which the males were reared both explain the patterns of worker reproduction found. Overall, our results suggest that the earlier evidence for facultative worker policing in D. saxonica may have been caused by accidental correlations with certain confounding variables, or, alternatively, that there are large interpopulation differences in the expression of worker policing.     

An alternative strategy for maintenance of eusociality after nest destruction: new nest construction in a primitively eusocial wasp

Although nests are central to colonial life in social insects, nests are sometimes damaged by predators or natural disasters. After nest destruction, individuals usually construct new nests. In this case, a sophisticated mechanism like the scent trail pheromone used in large insect colonies that recruit individuals to new nest sites would be important for the maintenance of eusociality. In independent-founding Polistes wasps, it is well known that queens enforce workers physiologically on the natal nests even if evidence of trail pheromone use has not been exhibited. We investigated the effect of the queen on an alternative strategy for the maintenance of eusociality by first females after nest destruction in the primitively eusocial wasp Polistes chinensis. We predicted that the first females in queen-absent colonies have various behavioral options after nest destruction. Even if the females construct new nests cooperatively with other individuals, the new nest construction should be conducted more smoothly in queen-present colonies because the queens regulate the behavior of wasps. We made wasps construct new nests by removing the entire brood from existing nests. The presence of the queen did not cause variation in the alternative strategy of the first females, as the first females (workers) usually constructed new nests cooperatively irrespective of the queen-presence. Thus, the workers in the queenpresent colonies affiliated to the new nest construction more smoothly and constructed new nests more efficiently than workers in the queen-absent colonies. Our results suggest that the presence of the queen is important for maintaining eusociality in primitively eusocial wasps after nest destruction. Received 8 February 2005; revised 5 October 2005; accepted 17 October 2005.     

Queen-worker conflict and social parasitism in bumble bees (Hymenoptera: Apidae)

Psithyrus ashtoni (Hymenoptera: Apidae) is an obligate, workerless bumble, bee social parasite which invades nests of Bombus affinis. Although parasites are limited by host worker defence to invading very small colonies, there is considerable flexibility in the way parasites control host brood bionomics once they are accepted inside the nest. A study of 46 parasitized and 22 non-parasitized laboratory colonies of B. affinis showed that P. ashtoni females cohabited with host queens and workers while the worker force increased, but not to the maximum normally achieved in non-parasitized nests. While colony reproductive success was correlated with the number of workers reared, parasites risked being killed or ejected from the comb by workers, after the queen had lost dominance. Host bees usually succeeded in rearing offspring, and Psithyrus reproductive success was related to the ability of parasites to control proportional investment in the two species. In addition to displacing P. ashtoni females, host bees ate the eggs of parasites and ejected their larvae. These behaviours were also exhibited by workers in the later stages of development of non-parasitized colonies. These results indicate that social parasites are at least partially subject to the conflict of genetic self-interest between the queen and her workers which is believed to influence the control of reproductive investment in haplodiploid Bombus societies.     

No evidence that reproductive bumblebee workers reduce the production of new queens

Kin selection theory predicts potential conflict between queen and workers over male parentage in hymenopteran societies headed by one, singly mated queen, because each party is more closely related to its own male offspring. In ‘late-switching’ colonies of the bumblebee Bombus terrestris, i.e. colonies whose queens lay haploid eggs relatively late in the colony cycle, workers start to lay male eggs shortly after the queen lays the female eggs that will develop into new queens. It has been hypothesized that this occurs because workers recognize, via a signal given by the queen instructing female larvae to commence development as queens, that egg laying is now in their kin-selected interest. This hypothesis assumes that aggressive behaviour in egg-laying workers does not substantially reduce the production of new queens, which would decrease the workers' fitness payoff from producing males. We tested the hypothesis that reproductive activity inB. terrestris workers does not reduce the production of new queens. We used microsatellite genotyping to sex eggs and hence to select eight size-matched pairs of ‘late-switching’ colonies from a set of commercial colonies. From one colony of each pair we removed every egg-laying or aggressive worker observed. From the other colony, we simultaneously removed a nonegg-laying, nonaggressive worker. Removed workers were replaced with young workers from separate colonies at equal frequencies within the pair. There was no significant difference in queen productivity between colonies with reduced or normal levels of egg-laying or aggressive workers. Therefore, as predicted, reproductive B. terrestris workers did not significantly reduce the production of new queens.     

The Use of the Vibration Signal and Worker Piping to Influence Queen Behavior during Swarming in Honey Bees, Apis mellifera

We investigated worker regulation of queen activity during reproductive swarming by examining the rates at which workers performed vibration signals and piping on queens during the different stages of the swarming process. Worker–queen interactions were first examined inside observation hives during the 2–3 wk that preceded the issue of the swarm (pre‐swarming period) and then inside the swarm clusters during the period that preceded liftoff and relocation to a new nest site (post‐swarming period). Queen court size did not differ between the pre‐ and post‐swarming periods, but workers fed the queens less inside the swarm clusters. Workers performed vibration signals on the queens at increasing rates throughout the pre‐swarming period inside the natal nest, but rarely or never vibrated the queen inside the swarm. Piping was performed on the queens during both the pre‐ and post‐swarming periods and always reached a peak immediately before queen flight. During the final 2–4 h before swarm liftoff, queens were increasingly contacted by waggle dancers for nest sites, some of which piped the queen. The vibration signal may operate in a modulatory manner to gradually prepare the queen for flight from the natal nest, and the cumulative effects of the signal during the pre‐swarming period may make further vibrations on the queen unnecessary when inside the swarm cluster. In contrast, worker piping may function in a more immediate manner to trigger queen takeoff during both the pre‐ and post‐swarming periods. Workers that vibrate and pipe the queen tend to be older, foraging‐age bees. The regulation of queen activity during colony reproduction may therefore be controlled largely by workers that normally have little contact with queens, but help to formulate colony reproductive and movement decisions.