Non-nestmate Workers Research Articles

Nestmate recognition in the Amazonian stingless bee Melipona paraensis.

Meliponine bees use chemical-based nestmate discrimination to protect their colonies from unrelated intruders. However, species from the Amazon basin are relatively poorly known from this perspective. Here, we investigated Melipona paraensis nestmate discrimination in different contexts (nests vs. neutral arenas), testing aggression in bees facing other bees varying in age and origin (same/different colony or a different kleptoparasitic meliponine species) or experimentally treated with odors from unrelated colonies. As expected, M. paraensis did not discriminate against callow non-nestmate workers with weak/undifferentiated chemical signatures. Workers specialized in nest defense aggressed intruders more often than non-specialized workers, but were less aggressive in neutral arenas than in the nest. Our study provides novel behavioral information relevant for social insect research and meliponiculture.

Antenna Cleaning Is Essential for Precise Behavioral Response to Alarm Pheromone and Nestmate-Non-Nestmate Discrimination in Japanese Carpenter Ants (Camponotus japonicus).

Simple SummaryGrooming is a common behavior in animals. It serves the function of removing foreign materials and excessive amounts of self-secreted materials from the body’s surface. Social insects, such as honeybees or ants, use various types of pheromones, some of which propagate information about the environment to conspecific individuals, for chemical communication. The individuals that receive such information can respond with suitable behaviors to protect themselves and their society. Hence, grooming is important for the maintenance of the correct performance of their sensory organs on antennae for pheromone perception. Here, we experimentally limited self-grooming of the antennae in workers of the Japanese carpenter ant (Camponotus japonicus) by removing a pair of antennal cleaning apparatuses from the forelegs and investigated their behavioral change in response to exposure to the alarm pheromone or to encounters with nestmates or non-nestmates. Comparisons between self-grooming-nonlimited and self-grooming-limited ants showed that the self-grooming-limited ants gradually exhibited decreased locomotion activity in their fight-or-flight response to the alarm pheromone and experienced increased failure in nestmate and non-nestmate discrimination. Thus, the results of the present study suggest that antennal sensory system maintenance supports social communication, which is indispensable not only to the individual workers but also to the survival of their society.Self-grooming of the antennae is frequently observed in ants. This antennal maintenance behavior is presumed to be essential for effective chemical communication but, to our knowledge, this has not yet been well studied. When we removed the antenna-cleaning apparatuses of the Japanese carpenter ant (C. japonicus) to limit the self-grooming of the antennae, the worker ants demonstrated the self-grooming gesture as usual, but the antennal surface could not be sufficiently cleaned. By using scanning electron microscopy with NanoSuit, we observed the ants’ antennae for up to 48 h and found that the antennal surfaces gradually became covered with self-secreted surface material. Concurrently, the self-grooming-limited workers gradually lost their behavioral responsiveness to undecane—the alarm pheromone. Indeed, their locomotive response to the alarm pheromone diminished for up to 24 h after the antenna cleaner removal operation. In addition, the self-grooming-limited workers exhibited less frequent aggressive behavior toward non-nestmate workers, and 36 h after the operation, approximately half of the encountered non-nestmate workers were accepted as nestmates. These results suggest that the antennal sensing system is affected by excess surface material; hence, their proper function is prevented until they are cleaned.

Ritualized aggressive behavior reveals distinct social structures in native and introduced range tawny crazy ants.

How workers within an ant colony perceive and enforce colony boundaries is a defining biological feature of an ant species. Ants fall along a spectrum of social organizations ranging from single-queen, single nest societies to species with multi-queen societies in which workers exhibit colony-specific, altruistic behaviors towards non-nestmate workers from distant locations. Defining where an ant species falls along this spectrum is critical for understanding its basic ecology. Herein we quantify queen numbers, describe intraspecific aggression, and characterize the distribution of colony sizes for tawny crazy ant (Nylanderia fulva) populations in native range areas in South America as well as in their introduced range in the Southeastern United States. In both ranges, multi-queen nests are common. In the introduced range, aggressive behaviors are absent at all spatial scales tested, indicating that within the population in the Southeastern United States N. fulva is unicolonial. However, this contrasts strongly with intraspecific aggression in its South American native range. In the native range, intraspecific aggression between ants from different nests is common and ritualized. Aggression is typically one-sided and follows a stereotyped sequence of escalating behaviors that stops before actual fighting occurs. Spatial patterns of non-aggressive nest aggregation and the transitivity of non-aggressive interactions demonstrate that results of neutral arena assays usefully delineate colony boundaries. In the native range, both the spatial extent of colonies and the average number of queens encountered per nest differ between sites. This intercontinental comparison presents the first description of intraspecific aggressive behavior for this invasive ant and characterizes the variation in colony organization in the native-range, a pre-requisite to a full understanding of the origins of unicoloniality in its introduced range.

Caste discrimination in the ant Odontomachus hastatus: What role for behavioral and chemical cues?

In social insects, the maintenance of genetic colony integrity requires resident workers to recognize any intruder with a reproductive potential and to behave appropriately to minimize fitness costs. In this study, our objective was to identify the relative contribution of the behavioral patterns and chemical cues of intruders with different fertility status on their likelihood of being accepted in monogynous colonies. Using the ponerine ant Odontomachus hastatus as a model organism, we introduced non-nestmate workers, founding queens and heterospecific workers on intact nests in the field. We demonstrated that resident workers were more aggressive toward founding queens than toward non-nestmates workers originating from the same or a distant population. Lab experiments showed that the patterns of aggression did not differ substantially between chilled and live ants, which suggests that chemical cues alone allow caste discrimination. However, the absence of behavioral cues produced more variable results in the outcome of interactions. We also showed that resident workers readily accepted non-nestmate mature queens. The analysis of cuticular profiles revealed that individuals belonging to different castes and fertility status have contrasted chemical signatures. Overall, our study revealed that workers exhibit a graded behavioral response depending on the reproductive status of intruders. We discussed the observed variation in the extent of aggression in relation to the potential fitness costs associated with acceptance or rejection error of individuals differing in fertility status.

Variation in nestmate recognition ability among polymorphic leaf-cutting ant workers

A key feature for the success of social insects is division of labour, allowing colony members to specialize on different tasks. Nest defence is a defining task for social insects since it is crucial for colony integrity. A particularly impressive and well-known case of worker specialization in complex hymenopteran societies is found in leaf-cutting ants of the genera Atta and Acromyrmex. We hypothesized that three morphological worker castes of Acromyrmex echinatior differ in their likelihood to attack intruders, and show that major workers are more aggressive towards non-nestmate workers than medium and minor workers. Moreover, minors do not discriminate between nestmate and non-nestmate brood, while larger workers do. We further show that A. echinatior ants use cuticular chemical compounds for nestmate recognition. We took advantage of the natural variation in the cuticular compounds between colonies to investigate the proximate factors that may have led to the observed caste differences in aggression. We infer that major workers differ from medium workers in their general propensity to attack intruders (the “action component” of the nestmate recognition system), while minors seem to be less sensitive to foreign odours (“perception component”). Our results highlight the importance of proximate mechanisms underlying social insect behaviour, and encourage an appreciation of intra-colony variation when analysing colony-level traits such as nest defence.

Specific recognition of reproductive parasite workers by nest-entrance guards in the bumble bee Bombus terrestris

BackgroundThe impact of social parasites on their hosts’ fitness is a strong selective pressure that can lead to the evolution of adapted defence strategies. Guarding the nest to prevent the intrusion of parasites is a widespread response of host species. If absolute rejection of strangers provides the best protection against parasites, more fine-tuned strategies can prove more adaptive. Guarding is indeed costly and not all strangers constitute a real threat. That is particularly true for worker reproductive parasitism in social insects since only a fraction of non-nestmate visitors, the fertile ones, can readily engage in parasitic reproduction. Guards should thus be more restrictive towards fertile than sterile non-nestmate workers. We here tested this hypothesis by examining the reaction of nest-entrance guards towards nestmate and non-nestmate workers with varying fertility levels in the bumble bee Bombus terrestris. Because social recognition in social insects mainly relies on cuticular lipids (CLs), chemical analysis was also conducted to examine whether workers’ CLs could convey the relevant information upon which guards could base their decision. We thus aimed to determine whether an adapted defensive strategy to worker reproductive parasitism has evolved in B. terrestris colonies.ResultsChemical analysis revealed that the cuticular chemical profiles of workers encode information about both their colony membership and their current fertility, therefore providing potential recognition cues for a suitable adjustment of the guards’ defensive decisions. We found that guards were similarly tolerant towards sterile non-nestmate workers than towards nestmate workers. However, as predicted, guards responded more aggressively towards fertile non-nestmates.ConclusionOur results show that B. terrestris guards discriminate non-nestmates that differ in their reproductive potential and respond more strongly to the individuals that are a greatest threat for the colony. Cuticular hydrocarbons are the probable cues underlying the specific recognition of reproductive parasites, with the specific profile of highly fertile bees eliciting the agonistic response when combined with non-colony membership information. Our study therefore provides a first piece of empirical evidence supporting the hypothesis that an adapted defensive strategy against worker reproductive parasitism exists in B. terrestris colonies.

The role of wax and resin in the nestmate recognition system of a stingless bee, Tetragonisca angustula

Recent research has shown that entrance guards of the stingless bee Tetragonisca angustula make less errors in distinguishing nestmates from non-nestmates than all other bee species studied to date, but how they achieve this is unknown. We performed four experiments to investigate nestmate recognition by entrance guards in T. angustula. We first investigated the effect of colony odours on acceptance. Nestmates that acquired odour from non-nestmate workers were 63% more likely to be rejected while the acceptance rate of non-nestmates treated with nestmate odour increased by only 7%. We further hypothesised that guards standing on the wax entrance tube might use the tube as an odour referent. However, our findings showed that there was no difference in the acceptance of non-nestmates by guards standing on their own colony’s entrance tube versus the non-nestmate’s entrance tube. Moreover, treatment of bees with nestmate and non-nestmate resin or wax had a negative effect on acceptance rates of up to 65%, regardless of the origin of the wax or resin. The role of resin as a source of recognition cues was further investigated by unidirectionally transferring resin stores between colonies. Acceptance rates of nestmates declined by 37% for hives that donated resin, contrasting with resin donor hives where acceptance of non-nestmates increased by 21%. Overall, our results confirm the accuracy of nestmate recognition in T. angustula and reject the hypothesis that this high level of accuracy is due to the use of the wax entrance tubes as a referent for colony odour. Our findings also suggest that odours directly acquired from resin serve no primary function as nestmate recognition cues. The lack of consistency among colonies plus the complex results of the third and fourth experiments highlight the need for further research on the role of nest materials and cuticular profiles in understanding nestmate recognition in T. angustula.

Brood adoption in the leaf-cutting ant Acromyrmex echinatior: adaptation or recognition noise?

The ability to discriminate between nestmates and non-nestmates is an important prerequisite for the evolution of eusociality. Indeed, social insect workers are typically able to discriminate between nestmate and non-nestmate workers. Adult non-nestmate workers are readily detected and rejected from the colony. Whether social insects can discriminate between nestmate and non-nestmate brood, however, is less clear. Here, we show that workers of the leaf-cutting ant Acromyrmex echinatior discriminate between nestmate and non-nestmate brood, and among brood of different stages. Initially, non-nestmate brood is attacked, but it is adopted after a delay. Adoption could occur due to inefficiency of the recognition system, or it could be adaptive because it is an inexpensive way to increase the workforce. Our results suggest that brood adoption may occur accidentally. We also report how workers replace fungal hyphae on the brood’s surface before transporting the brood into their fungus garden.

Intercolony transplantation of Oecophylla smaragdina (Hymenoptera: Formicidae) larvae

Oecophylla ants are utilized for biological control in fruit plantations in Australia and Asia. In Asia, queen larvae and alates are sold on commercial markets for human and animal consumption. This double utilization has induced an increasing interest in the domestication of these ants, but attempts to rear live colonies have been hindered partly by the length of time it takes from the founding of a colony until it can be utilized commercially. Early growth of a colony may be increased if ants from other colonies are adopted. The present experiments show that Oecophylla smaragdina larvae transplanted from other colonies are readily tolerated by non-nestmate workers and are reared to imagos. These results are fundamental for the future domestication of Oecophylla and elucidate the need for further studies of chemical nestmate recognition.

Nest defence in a stingless bee: What causes fighting swarms in Trigona carbonaria (Hymenoptera, Meliponini)?

The Australian stingless bee Trigona carbonaria sometimes displays a striking collective behaviour, known as a ‘fighting swarm’ in which thousands of workers fight and die. Molecular analysis of eight naturally-occurring fights showed they almost always comprise just two colonies, one of which is located within 2 m of the fight. Fighting swarms were experimentally triggered by manipulating colonies so that they received non-nestmate workers. Combined, our investigations suggest that T. carbonaria fighting swarms arise as a collective defence of the nest from conspecific invasion (e.g. robbery or nest usurpation)

Nestmate recognition by guards of the Asian hive bee Apis cerana

When a honey bee colony becomes queenless and broodless its only reproductive option is for some of its workers to produce sons before the colony perishes. However, for this to be possible the policing of worker-laid eggs must be curtailed and this provides the opportunity for queenless colonies to be reproductively parasitized by workers from other nests. Such reproductive parasitism is known to occur in Apis florea and A. cerana. Microsatellite analyses of worker samples have demonstrated that the proportion of non-natal workers present in an A. cerana colony declines after a colony is made queenless. This observation suggests that queenless A. cerana colonies may be more vigilant in repelling potentially parasitic non-natal workers than queenright colonies. We compared rates of nestmate and non-nestmate acceptance in both queenright and queenless A. cerana colonies using standard assays and showed that there is no statistical difference between the proportion of non-nestmate workers that are rejected in queenless and queenright colonies. We also show that, contrary to earlier reports, A. cerana guards are able to discriminate nestmate workers from non-nestmates, and that they reject significantly more non-nestmate workers than nestmate workers.

Odour transfer in stingless bee marmelada (Frieseomelitta varia) demonstrates that entrance guards use an “undesirable–absent” recognition system

In group-level recognition, discriminators use sensory information to distinguish group members and non-members. For example, entrance guards in eusocial insect colonies discriminate nestmates from intruders by comparing their odour with a template of the colony odour. Despite being a species-rich group of eusocial bees closely related to the honey bees, stingless bee nestmate recognition is a relatively little-studied area. We studied Frieseomelitta varia, a common Brazilian species of stingless bee known as marmelada. By measuring the rejection rates of nestmate and non-nestmate worker bees by guards, we were able to show that guards became significantly less accepting (from 91 to 46%) of nestmates that had acquired odour cues from non-nestmate workers; however, guards did not become significantly more accepting (from 31 to 42%) of non-nestmates that had acquired equivalent amounts of odour cues from the guard's nestmates. These data strongly suggest that guards use an "undesirableabsent" system in recognition, whereby incoming conspecific workers are only accepted if undesirable cues are absent, despite the presence of desirable cues. We suggest that an undesirableabsent system is adaptive because robbing by conspecifics may be an important selective factor in F. varia, which would lead to selection for a non-permissive acceptance strategy by guards.

Caste-biased acceptance of non-nestmates in a polygynous ponerine ant

We investigated the influence of caste on nestmate discrimination in the ponerine ant Pachycondyla luteipes, where workers lack functional ovaries and are totally sterile. Both a mark-and-recapture field experiment and an introduction experiment in the laboratory revealed intermixing of both nestmate and non-nestmate workers between nests. In the laboratory experiment, conspecific workers, both nestmate and non-nestmates, were almost always accepted. Workers' internest hostility was weak and did not correlate with the distance between nests over the geographical scale studied (<130 m). However, workers responded differentially to nestmate and non-nestmate workers, grooming non-nestmates more frequently than nestmates. In contrast, non-nestmate queens were usually violently attacked by resident workers, and as a result only 30% were accepted. Nestmate queens were always accepted with no aggression. Our results indicate that P. luteipes workers have the ability to recognize nestmates but are not aggressive when the non-nestmates are sterile workers. Such caste-biased acceptance has been predicted by kin selection in relation to the avoidance of intraspecific social parasitism and regulation of queen numbers.

Social parasitism by Cape honeybee workers in colonies of their own subspecies (Apis mellifera capensis Esch.)

Social parasitism is widespread in the eusocial insects. Although social parasites often show a reduced worker caste, unmated workers can also parasitize colonies. Cape honeybee workers, Apis mellifera capensis, can establish themselves as social parasites in host colonies of other honeybee subspecies. However, it is unknown whether social parasitism by laying workers also occurs among Cape honeybee colonies. In order to address this question we genotyped worker offspring of six queenless A. m. capensis colonies and determined the maternity of the reproducing workers. We found that three non-nestmate workers dominated reproduction in a host colony and produced 62.5% of the progeny. Our results show that social parasitism by laying workers is a naturally occurring part of the biology of Cape honeybees. However, such social parasitism is not frequently found (6.41% of the total worker offspring) probably due to co-evolutionary processes among A. m. capensis resulting in an equilibrium between selection for reproductive dominance in workers, colony maintenance and queen adaptation.

The chemical basis for trail recognition in Lasius nipponensis (Hymenoptera: Formicidae)

In this paper we report on the chemical basis for trail recognition in Lasius nipponensis. On and near trails in the field, workers became aggressive against conspecific intruders and succeeded in protective contests, while intruders usually avoided confrontation. Such asymmetric interactions were also observed in the laboratory when two non-nestmate workers were sequentially placed in a clean glass dish, while mutual aggression was observed when they were placed simultaneously. Asymmetric aggression was also observed when the workers were placed in a dish previously conditioned by other workers, or when the dish was treated with the hexane rinse of the conditioned dish. The rinse contained a series of hydrocarbons, in which components and proportion were almost identical to those of the cuticular hydrocarbons of the workers, except for a lack of n-alkanes. Amounts of the hydrocarbons that remained on the dish were very small when all the tarsi of the workers were incapacitated. We therefore consider that the hydrocarbons are not adhesion of the cuticular hydrocarbons but secretion from the tarsi of workers, and serve as a key signal for trail recognition in this ant.

Host Location Behavior in a Parasitoid of Imported Fire Ants

Female parasitoids use a hierarchy of cues to locate suitable hosts. We conducted a series of field observations and experiments to examine host location behavior in Pseudacteon tricuspis Borgmeier, a phorid parasitoid of Solenopsis invicta Buren worker ants. The parasitoids were frequently attracted to host workers at disturbed colonies, but were almost never attracted to host workers foraging at baits. When conspecific nonnestmate workers were introduced to baits, resulting in aggressive interactions, parasitoids appeared at the majority of baits. Moreover, larger numbers of parasitoids appeared at baits to which greater numbers of nonnestmate workers had been added. Addition of nonnestmate workers to disturbed colonies resulted in increased numbers of parasitoids attracted. Pseudacteon tricuspis did not display a pattern of uniform distribution at disturbed colonies but often was very abundant at some colony locations while absent or rare at nearby colony locations. Solenopsis invicta workers release alarm pheromones in aggressive interactions with nonnestmates, and this substance is likely an important chemical cue that attracts P. tricuspis flies to host workers from a distance.

Parasitic Cape honey bee workers ( Apis mellifera capensis ) are not given differential treatment by African guards ( A. m. scutellata )

Workers of the Cape honey bee Apis mellifera capensis started to parasitize the African honey bee A. m. scutellata after being introduced into Gauteng (former Northern Transvaal Province) from its native territory, the Cape Province. The A. m. capensis strain that is parasitic has at least two traits that make it a serious pest of the native African bee colonies: workers rapidly develop their ovaries when in a non-capensis colony even when a queen is present, and worker-laid eggs are not killed by worker policing. Here we investigate whether A. m. capensis workers also have special mechanisms to circumvent the guard bees of A. m. scutellata thereby aiding their horizontal transmission between infected and non-infected colonies. We studied the acceptance of non-nestmateA. m. capensis and A. m. scutellata bees by guards of African bee colonies by introducing them to the hive entrance of A. m. scutellata colonies. We used 2 A. m. scutellata discriminator colonies that were both split into a queenright and a queenless portion. Our results suggest that invading workers of A. m. capensis have no special mechanisms to circumvent the African guards. Neither race of the introduced bee nor presence or absence of the queen in the guarding colony affected the proportion of introduced workers accepted. When pooled, 15% of introduced A. m. capensis and 18% of A. m. scutellata non-nestmate workers were accepted by African guards.

Queen primer pheromone affects conspecific fire ant ( Solenopsis invicta ) aggression

Monogyne fire ant, Solenopsis invicta, colony workers are territorial and are aggressive toward members of other fire ant colonies. In contrast, polygyne colony workers are not aggressive toward non-nestmates, presumably due to broader exposure to heritable and environmentally derived nestmate recognition cues (broad template). Workers from both monogyne and polygyne fire ant colonies execute newly mated queens after mating flights. We discovered that monogyne and polygyne queens have a remarkable effect on conspecific recognition. After removal of their colony queen, monogyne worker aggression toward non-nestmate conspecifics quickly drops to merely investigative levels; however, heterospecific recognition/aggression remains high. Queenless monogyne or polygyne worker groups were also not aggressive toward newly mated queens. Queenless worker groups of both forms that adopted a monogyne-derived newly mated queen became aggressive toward non-nestmate workers and newly mated queens. We propose that the powerful effect of fire ant queens on conspecific nestmate recognition is caused by a queen-produced recognition primer pheromone that increases the sensitivity of workers to subtle quantitative differences in nestmate recognition cues. This primer pheromone prevents the adoption of newly mated queens (regulation of reproductive competition) in S. invicta and when absent allows queenless workers to adopt a new queen readily. This extraordinary discovery has broad implications regarding monogyne and polygyne colony and population dynamics.

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

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.

Fate of Newly Mated Queens Introduced into Monogyne and Polygyne &lt;I&gt;Solenopsis invicta&lt;/I&gt; (Hymenoptera: Formicidae) Colonies

Nestmate recognition is of prime importance in maintaining ant colony integration and organization. Monogyne red imported fire ant, Solenopsis invicta Buren, colonies are highly territorial and aggressive toward non-nestmate conspecific workers. In contrast, workers from polygyne nests in the United States show no aggression toward workers from other conspecific colonies (polygyne or monogyne). Nests within a polygyne population form a ‘supercolony,’ with free exchange of workers and food between nests. The difference in conspecific nestmate recognition is a major distinguishing feature of the two S. invicta forms in the United States. We report here the discovery of an exception to this dichotomy. High levels of worker aggression are released by the introduction of newly mated queens into both polygyne and monogyne colonies. This suggests that nestmate recognition involving female sexuals does not follow the same mechanism used to explain nestmate recognition behavior between workers.