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 relationship between the distribution of worker sizes and new worker production in the ant Formica neorufibarbis

While it is commonly assumed that variation in worker sizes within a single ant colony increases colony efficiency, there is little causal evidence of a link between worker size variation and colony performance. I tested whether the range of worker sizes within colonies of the ant species Formica neorufibarbis affected new worker production. Removing large workers from colonies lowered the rate of new worker production. A study of unmanipulated colonies indicated that colonies did not maintain a full range of worker sizes; mean worker head widths varied from 0.89-1.24 mm. Colonies naturally missing large workers did not have lower rates of worker production, suggesting that the relative size, not the absolute size, of workers within colonies was important. These are the first results to directly link the range of worker sizes to a component of colony fitness in a natural setting.     

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.     

Colony fusion in a termite: What makes the society "open"?

Summary. Sociobiological theories assume that insect societies are closed, i.e., members always act aggressively toward alien conspecific individuals. However, introduction of non-nestmate workers into a host colony of a lower termite, Reticulitermes speratus revealed various levels of agonism: from genocide to colony fusion. Members of the host colony attacked and killed the intruders having a higher nymph ratio (the number of nymphs/the number of workers) than the host colony had. In contrast, the intruders were accepted if they had a lower nymph ratio than the host colony. Acceptance of a lower-nymph-ratio colony could be beneficial for the host colony because it would gain additional labor force to feed its own nymphs. However, acceptance of a higher-nymph-ratio colony might be disadvantageous because the workers must rear non-relative nymphs additionally. Here we show that termites facultatively change their agonistic response toward non-nestmates according to the cost and benefit of colony fusion. Contrary to the existent concept, we report for the first time that colony fusion is an adaptive tactic in social insects.     

Comparing mark-recapture and constant removal protocols for estimating forager population size of the subterranean termite Coptotermes lacteus (Isoptera: Rhinotermitidae)

Forager population sizes of colonies of Coptotermes lacteus(Froggatt) in New South Wales were estimated using two methods: mark-recapture and constant removal, in two disturbed habitats: a pine plantation and cleared farmland. Mark-recapture population estimates were unrealistic and unreliable: they could be improbably large, over 200 million foragers, and they varied enormously between samples for each colony without any pattern. The constant removal population estimates could also be unrealistic: they could be negative or quite different when calculated using regression and maximum likelihood methods. However, the unrealistic results could be predicted reliably, and explained by the lack of re-contact with the sampling devices (bait stations) - a violation of an assumption of the method. This happened more frequently in the plantation than in the farmland, probably because of the greater abundance of alternative food sources in the plantation. Of the two methods, constant removal provided reasonable forager population estimates, relative to direct counts, at least some of the time, plus a mechanism by which reliability could be tested, whereas mark-recapture provided neither. Further refinement and testing of constant removal methods are urged to provide a more reliable population estimation technique for termites.     

Allometry in the giant tropical ant, Paraponera clavata

Summary: Workers of the ponerine ant, Paraponera clavata, grow allometrically, with the head disproportionately larger in larger workers. The anterior (clypeus)-posterior (occiput) dimension of the head capsule is allometric with the lateral (interocular) dimension, so that larger workers have elongate heads. The degree of head capsule allometry varies among colonies; this could result either from differences in colony maturity or from variation in developmental patterns among colonies. These data resolve a previously controversial issue concerning caste in Paraponera clavata.     

Yoyo-bang: a risk-aversion investment strategy by a perennial insect society

In 1978, Oster and Wilson proposed a bang-bang investment strategy for social insects in which colony size at maturity amplifies colony reproduction. In this paper, the investment strategies of the monogyne form of the fire ant, Solenopsis invicta, were compared to the predictions of the bang-bang model. Demographic census data, collected on fire ant mounds excavated every month during the years 1985 and 1988, revealed that colony reproduction was independent of colony size (~50,000 to ~250,000 workers). Why were mature S. invicta colonies up to five times larger than they needed to be to reproduce an annual batch of sexual offspring? To address this question, Oster and Wilson's bang-bang model was modified to a "yoyo-bang" investment strategy for perennial societies. In the yoyo-bang model, excess workers are a disposable reserve - a buffer - that can oscillate up or down depending on resource availability without adversely affecting annual reproductive cycles. The yoyo-bang model links colony size, colony survival and lifetime reproductive fitness.     

Reproductive strategy in orphaned colonies of Myrmica kotokui Forel, the Japanese species of the M. ruginodis complex (Hymenoptera, Formicidae)

Summary: The reproductive strategy between queen-right and orphaned colonies of Myrmica kotokui was compared. The ratio of orphaned colonies reached about 30 percent in the field. Although colony size was significantly smaller in orphaned colonies, the mean body size and mean ovariole length of the workers were significantly larger than those in queen-right colonies. The reproductive individuals in orphaned colonies were also significantly larger than those in queen-right colonies. Only 38.5 % of the orphaned colonies, however, contained eggs during the reproductive season, compared to 100 % of the queen-right colonies. This indicates that worker reproduction under natural conditions is relatively low, even in orphaned colonies.     

Nest site selection and longevity in the ponerine ant Rhytidoponera metallica (Hymenoptera, Formicidae)

Summary: The size of the nesting cavity and the nature of the nest-building material can constrain colony growth in eusocial insects. Rocks protect colony members against extreme temperatures as well as serve as a supplementary source of heat, thereby maintaining optimal conditions for brood development. The frequency distribution of available rocks and those occupied by colonies of Rhytidoponera metallica in the Avon River State Forest, Victoria, Australia, showed that colonies of R. metallica avoided nesting under small rocks (<200 cm²). A strong correlation between colony size and rock size indicates that nesting under a larger rock promotes colony growth. Laboratory choice experiments revealed that workers are capable of recognizing larger rocks from external physical characters (dimension). Field data indicates that colonies leave nests frequently, with nest abandonment peaking in the summer months.     

Optional gamergates in the queenright ponerine ant Gnamptogenys striatula Mayr

Summary: Ponerine ants display a number of social structures to which particular behaviours are associated. In the ponerine ant species Gnamptogenys striatula Mayr, queens occur and queenright colonies are functionally polygynous. However, some workers are capable to mate and to produce their own worker offspring. These gamergates appear several days after the queens are experimentally removed, allowing some workers to adopt a sexual calling posture inside the nest. At that time, other workers get outside the nest to collect males in the arena and carry them back into the colony. There, these males are groomed before they can mate with sexual calling workers. As for queens, several gamergates may coexist in a same colony. The social profile of gamergates is similar to those of nurses and they stay closer to the egg piles.     

Size variation and foraging rate in bumblebees (Bombus terrestris)

Summary: Size polymorphism is an important life history trait in bumblebees with strong impact on individual behavior and colony organization. Within a colony larger workers tend to serve as foragers, while smaller workers fulfill in-hive tasks. It is often assumed that size-dependent division of labor relates to differences in task performance. In this study we examined size-dependent interindividual variability in foraging, i.e. whether foraging behavior and foraging capability of bumblebee workers are affected by their size. We observed two freely foraging Bombus terrestris colonies and measured i) trip number, ii) trip time, iii) proportion of nectar trips, and iv) nectar foraging rate of different sized foragers. In all observation periods large foragers exhibited a significantly higher foraging rate than small foragers. None of the other three foraging parameters was affected by worker size. Thus, large foragers contributed disproportionately more to the current nectar influx of their colony. We provide a detailed discussion of the possible proximate mechanisms underlying the differences in foraging rate.     

Sex ratios and the distribution of elaiosomes in colonies of the ant, Aphaenogaster rudis

Summary: Genetic theory predicts that workers in monogynous ant colonies with singly-mated queens should capitalize on higher relatedness with sisters than with brothers by altering the sex investment ratio of a colony in favor of females. Sex investment ratios, however, may also be influenced by the amount of resources available to colonies, in part because more mating opportunities might be obtained by investing scarce resources in males, which are much smaller than queens. Female larvae that reach a critical size by a particular point in development become queens while underfed larvae develop into workers, so workers could potentially influence the sex investment ratio of a colony by selectively feeding female larvae. In a previous experiment on the ant, Aphaenogaster rudis, colonies increased female sex investment after their diet was supplemented with elaiosomes, a lipid-rich food gained from a seed dispersal mutualism. In order to investigate the mechanisms producing this shift, we radio-labeled Sanguinaria canadensis elaiosomes with fatty acids and compared uptake among castes within a colony. The experiment was performed in both the laboratory and field. Lab colonies produced female-biased sex investment ratios, while field colonies mainly invested in males. We hypothesize that this discrepancy is related to differing levels of background food availability in the lab and field. The results of the elaiosome distribution experiment do not support a hypothesis that elaiosomes play a qualitative role in queen determination, because all individuals in a colony receive this nutrient. There is, however, support for the hypothesis that elaiosomes have a quantitative effect on larval development because larvae that accumulated more radio-label from elaiosomes tended to develop into gynes (virgin queens), while other female larvae developed into workers.     

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.     

How does colony growth influence communication in ants?

Summary. As Lasius niger societies grow from incipient nests to mature colonies, their foraging strategies shift from the individual exploitation of food sources to mass recruitment. Colony size instead of age is the key factor that shapes the exploratory and foraging responses of Lasius niger: a drastic reduction (or increase) of the population elicits an activity profile similar to that observed in younger (or older) societies of the same size. As a colony grows, the proportion of patrollers significantly decreases while the proportion of conveyors remains rather constant. As regards the energetic return, it increases with incipient nest size due to the replacement of minims by ordinary workers of larger crop capacity. We also demonstrate that minims of incipient nests modulate their trail-laying behaviour according to the social context, in this case the colony size. During their ontogenesis, L. niger colonies exhibit a progressive integration of individual foragers into a network of communication, the adaptive significance of which is discussed.     

Natural patterns of caste and sex allocation in the stingless bees <Emphasis Type="Italic">Melipona favosa</Emphasis> and <Emphasis Type="Italic">M. trinitatis</Emphasis> related to worker behaviour

Summary. This paper is the report of a long-duration study of the production of gynes and males in Melipona stingless bees in Trinidad and Tobago, including a behavioural study of laying workers. In 167 brood samples (16342 pupae) of M. favosa, taken from 78 colonies in the natural environment over the years 1993-2001, workers represented 78.4% and males represented 17.3%. Gynes represented 5.1% of all female brood. Gyne proportion never exceeded 22.5%. Gynes were found to be common throughout the year. Like the gynes, males were present all year, but their occurrence varied over the months. Males were most common in the months of July and August. At the colony level male occurrence in the brood was characterized by very high values (maximum 74.2%), next to a frequent complete absence (in 26.5% of all samples). The finding of bout-like production of males at the colony level is supported by the observations on reproductive worker behaviour. The colonies appeared to be in different phases of male production. When male producing laying workers were present, they competed heavily for egg-laying opportunities. Various behaviours of laying workers and the queen are described and interpreted on the basis of reproductive competition and kin conflict theories. From these results, we conclude that in M. favosa, workers have a distinct influence on reproduction, including the production of gynes and males.     

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.     

Size and composition of swarming colonies in Provespa anomala (Hymenoptera, Vespidae), a nocturnal social wasp

Summary: Ninety-eight nests of various growing stages of Provespa anomala were found in the lowlands of Sumatra, Indonesia, from August to January. Its colony cycle is considered to be annual, with nests built throughout the year. There were two types of early nests before the emergence of workers, one with a worker number of less than 63 and the other of more than 231. The former were new nests, each containing a new queen and were built by reproductive swarming, whereas each of the latter was possibly re-built by an old queen and an absconding swarm. Ten swarming colonies were attracted by an oil-lamp light; these consisted of a copulated queen with immature oocytes in the ovary and 55 workers on average. No males, or workers stylopized by Xenos provesparum were observed either in colonies before worker emergence or in swarms coming flying into the light. Differences between swarming in Provespa, polygyny and nest relocation in Vespa, and those in swarm-founding Polistinae are discussed.     

Estimating relative decline in populations of subterranean termites (Isoptera: Rhinotermitidae) due to baiting.

Although mark-recapture protocols produce inaccurate population estimates of termite colonies, they might be employed to estimate a relative change in colony size. This possibility was tested using two Australian, mound-building, wood-eating, subterranean Coptotermes species. Three different toxicants delivered in baits were used to decrease (but not eliminate) colony size, and a single mark-recapture protocol was used to estimate pre- and postbaiting population sizes. For both species, the numbers of termites retrieved from bait stations varied widely, resulting in no significant differences in the numbers of termites sampled between treatments in either the pre- or postbaiting protocols. There were significantly fewer termites sampled in all treatments, controls included, in the postbaiting protocol compared with the pre-, suggesting a seasonal change in forager numbers. The comparison of population estimates shows a large decrease in toxicant treated colonies compared with little change in control colonies, which suggests that estimating the relative decline in population size using mark-recapture protocols might to be possible. However, the change in population estimate was due entirely to the significantly lower recapture rate in the control colonies relative to the toxicant treated colonies, as numbers of unmarked termites did not change between treatments. The population estimates should be treated with caution because low recapture rates produce dubious population estimates and, in some cases, postbaiting mark-recapture population estimates could be much greater than those at prebaiting, despite consumption of bait in sufficient quantities to cause population decline. A possible interaction between fat-stain markers and toxicants should be investigated if mark-recapture population estimates are used. Alternative methods of population change are advised, along with other indirect measures.     

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.     

Effects of colony-level attributes on larval feeding in the fire ant, Solenopsis invicta

Summary: Do colony attributes modulate individual behavior? The effects of colony size and worker:brood ratio on the rate of worker-to-larva trophallaxis in the fire ant, Solenopsis invicta, were investigated. Neither colony size ranging from 100 to 10,000 nor worker:brood ratio ranging from 1:1 to 16:1 affected the density of workers on the brood pile, nor the rate or duration of worker-to-larva trophallaxis. The demands of hungry larvae were met even in groups as small as 100 workers in worker:brood ratios as small as 1. Only when the worker:brood ratio was less than 1, were larvae tended or fed at reduced rates. Under natural conditions, this occurs only in incipient colonies. Otherwise, in post-incipient colonies, the flow of food to larvae was unmodified by colony attributes. The implications of this finding are two-fold: First, it reinforces previous research demonstrating that social feeding in the fire ant emerges from localized interactions rather than mass communication. Second, it highlights the resiliency of this weedy species. Hypothetically, colonies drastically reduced by catastrophic events such as flooding should still be able to produce sexuals.