Host Workers Research Articles

Comparative analyses of caste, sex, and developmental stage-specific transcriptomes in two Temnothorax ants.

Social insects dominate arthropod communities worldwide due to cooperation and division of labor in their societies. This, however, makes them vulnerable to exploitation by social parasites, such as slave‐making ants. Slave‐making ant workers pillage brood from neighboring nests of related host ant species. After emergence, host workers take over all nonreproductive colony tasks, whereas slavemakers have lost the ability to care for themselves and their offspring. Here, we compared transcriptomes of different developmental stages (larvae, pupae, and adults), castes (queens and workers), and sexes of two related ant species, the slavemaker Temnothorax americanus and its host Temnothorax longispinosus. Our aim was to investigate commonalities and differences in group‐specific transcriptomes, whereupon across‐species differences possibly can be explained by their divergent lifestyles. Larvae and pupae showed the highest similarity between the two species and upregulated genes with enriched functions of translation and chitin metabolism, respectively. Workers commonly upregulated oxidation‐reduction genes, possibly indicative of their active lifestyle. Host workers, but not workers of the slavemaker, upregulated a “social behavior” gene. In slavemaker queens and workers, genes associated with the regulation of transposable elements were upregulated. Queens of both species showed transcriptomic signals of anti‐aging mechanisms, with hosts upregulating various DNA repair pathways and slavemaker queens investing in trehalose metabolism. The transcriptomes of males showed enriched functions for quite general terms realized in different genes and pathways in each species. In summary, the strong interspecific commonalities in larvae, pupae, and workers were reflected in the same enriched Gene Ontology (GO) terms. Less commonalities occurred in the transcriptomes of queens and males, which apparently utilize different pathways to achieve a long life and sperm production, respectively. We found that all analyzed groups in this study show characteristic GO terms, with similar patterns in both species.

Not too big, not too small: raids at moderately sized hosts lead to optimal outcomes for a slave-making ant

Understanding the trajectory of host-parasite co-evolution requires knowledge of how hosts and parasites impact one another’s fitness, especially among the avian and insect social parasites. Host choice is an important first step in this process, but the principles guiding host choice are unresolved, especially for specialist parasites choosing among individual hosts with multiple traits. To determine how parasites weigh various host traits relative to others, we need to identify their costs and benefits. Here I use the slave-making ant, Temnothorax americanus, to investigate the payoffs from different host trait combinations. I measured the costs and benefits of raids at hosts that varied in their value (# brood), defensive power (# workers), or their ratios. Additionally, I investigated whether slave-maker fighting power influences which host trait combinations were optimal. Slave-makers performed best when hosts contained more brood but fewer workers. However, the ability to maximize this ratio is constrained by the correlation of brood and worker numbers in natural nests, making the optimal host moderately sized. Measures of costs reinforce this conclusion, since slave-maker mortality increased with the number of host workers. Additionally, I found that larger slave-maker colonies have higher payoffs at larger hosts, suggesting their optimal host trait profile differs from smaller colonies. This study shows that social parasites exercising force ought to balance a trade-off between host value and defensibility, rather than maximizing only value. Furthermore, the results highlight that host demography could play a larger role in insect social parasite arms races than previously appreciated. A key to understanding the outcome of co-evolutionary arms races in social parasites is identifying the traits that contribute to the success of parasites and hosts. Host choice determines which traits experience selection, but the relative costs and benefits associated with different host traits, and how parasites ought to weigh them, remains unclear. I measure parasite success in relation to host and parasite demographic traits to distinguish the relative impacts of each using a slave-making ant. Maximizing host brood-to-worker ratio leads to higher payoffs, while the most populous hosts are impenetrable. These findings provide evidence that social parasites attacking by force seek a balance between a host’s value and defensibility, even if it means forgoing hosts with higher potential value. This in turn highlights colony demography and life history as important host traits under selection in co-evolutionary arms races in social insect parasites.

Behavior in Transition: Recovery of Behavior by an Obligate Parasitic Ant (Formica subintegra) Following Host Removal

Dulosis is a type of social parasitism in which a parasitic ant has become dependent on captured workers (hosts) of a closely related species. Dulosis can be either facultative or obligate depending on the degree of dependence on host workers. As parasites become more specialized over evolutionary time, their domestic abilities degenerate until they become unable to survive without the host. However, depending on the degree of specialization, the “lost” behaviors may display some degree of recovery when host workers are unavailable to do the tasks. The 12 species of the Formica sanguinea group are all traditionally considered to be facultative parasites. However, recent studies suggest that one member of the group, F. subintegra, has characteristics that are more consistent with obligate parasitism. To explore the degree to which F. subintegra has become obligate, this study examined the degree of recovery of foraging and nest excavation behaviors of parasites when hosts are removed. When parasites were isolated from hosts, they spent more time foraging and feeding regurgitated food to nestmates (oral trophallaxis), and tended to begin feeding sooner following a period of fasting than when hosts were present. Isolated parasites were able to excavate suitable tunnels and engaged in nest building behavior significantly more often than parasites in groups with hosts. These results indicate that F. subintegra demonstrates some recovery of its foraging and nest excavation abilities, and can be considered a less specialized (more primitive) obligate parasite. Formica subintegra and its facultative relatives can be used as models for studying the progression of dulotic evolution within a closely related group of social parasites, and may shed light on which factors contribute to the transition from facultative to obligate parasitism.

The possible role of ant larvae in the defence against social parasites.

Temporary social parasite ant queens initiate new colonies by entering colonies of host species, where they begin laying eggs. As the resident queen can be killed during this process, host colonies may lose their entire future reproductive output. Selection thus favours the evolution of defence mechanisms, before and after parasite intrusion. Most studies on social parasites focus on host worker discrimination of parasite queens and their offspring. However, ant larvae can also influence brood composition by consuming eggs. This raises the question whether host larvae can aid in preventing colony takeover by consuming eggs laid by parasite queens. To test whether larvae could play a role in anti-parasite defence, we compared the rates at which larvae of a common host species, Formica fusca, consumed eggs laid by social parasite, non-parasite, nest-mate, or conspecific non-nest-mate queens. Larvae consumed social parasite eggs more than eggs laid by a heterospecific non-parasite queen, irrespective of the chemical distance between the egg cuticular profiles. Also, larvae consumed eggs laid by conspecific non-nest-mate queens more than those laid by nest-mate queens. Our study suggests that larvae may act as players in colony defence against social parasitism, and that social parasitism is a key factor shaping discrimination behaviour in ants.

Host following of an ant associate during nest relocation

Ant nests are relatively stable and long-lasting microhabitats that attract a diverse group of arthropods. Particular stressors, however, can trigger ants to relocate their nest to a new site. It is unclear how associated arthropods respond to occasional nest moving of their host. Here, I report field observations which showed that the potentially parasitic larvae of the beetle Clytra quadripunctata follow their red wood ant host during nest relocation, either by crawling on their own or by being carried by the host workers. These observations shed new light on the spatial dynamics between ants and their associates.

Termitariophily: expanding the concept of termitophily in a physogastric rove beetle (Coleoptera: Staphylinidae)

1. Termitophily in some rove beetles is commonly attributed to the striking termite worker resemblance that is provided by the beetles' hypertrophic (‘physogastric’) abdomen. However, a termite nest may offer to a termitophile additional benefits, such as a continuously repaired shelter.2. This could apply to Corotoca melantho (Aleocharinae: Corotocini), a viviparous obligatory termitophile staphylinid beetle species. While conferring morphological congruence to its host worker termites, its physogastry may impair mobility, leading to vulnerability and the need for a secure environment. It seems plausible to hypothesise that physogastry in C. melantho would imply in interactions between this termitophile and its host termites as well as its host termitarium.3. This study provides evidence to build such a hypothesis by inspecting the morpho‐anatomical reproductive traits of this termitophile. It was found that a gradient of growth stages of embryos and larvae in the oviduct explains physogastry in females while pointing to iteroparity. The asynchronous development of oocytes in females, combined with a full developing sequence of sperm cells indicative of continuous spermatogenesis in males, suggests frequent matings.4. While improving guest–host similarity, physogastry and flightlessness should confer vulnerability to pregnant females, forcing C. melantho to seek close and sheltered environments. These could facilitate the frequent male–female contacts demanded by iteroparity. It is possible, therefore, that physogastry in C. melantho is not only associated with the termites themselves but also with the physical structure of the termitarium. Thus, C. melantho can be hypothesised to be a termitariophile in addition to being a termitophile.

“The road to reproduction”: foraging trails of Constrictotermes cyphergaster (Termitidae: Nasutitermitinae) as maternities for Staphylinidae beetles

Corotoca (Coleoptera: Staphylinidae) beetles are known for their close integration in the nests of the termite Constrictotermes cyphergaster (Termitidae: Nasutitermitinae). Although this relationship is regarded as ancient, many details are still obscure, such as their reproduction and the processes that lead to the dispersal of new beetles. We observed the use of termite foraging trails by Staphylinidae females to deposit and disperse their larvae. We recorded the deposition of larvae of C. melantho, C. fontesi, and C. sp. n. on the dorsal surfaces of termite host workers. The workers continue to follow the foraging trail until the newborn larvae freed themselves and fell into the leaf litter, subsequently burrowing into the ground. Information regarding the life stages of those Staphylinidae larvae outside the termite nest is important to understanding their full lifecycle as those taxa have strong relationships with the nest environment but also require dispersal strategies.

Survivorship and walking behavior of Inquilinitermes microcerus (Termitidae: Termitinae) in contact with host workers and walls from host nest

Constrictotermes sp. nests are frequently inhabited by colonies of Inquilinitermes microcerus. In this association, I. microcerus colonies usually establish their colonies spatially isolated from Constrictotermes colonies. Here, we investigated whether the apparent spatial isolation of I. microcerus colonies in Constrictotermes nests should be related to their needs (e.g. feeding) in relation to the central part of the nest or to a possible stress provoked by the presence of the host. For this, survival and walking behavior bioassays were performed to test the hypothesis that the survivorship of inquilines is: (i) reduced in the presence of host, mainly of those from different nests, (ii) increased in contact with inner walls compared with external walls; and that the distance walked and walking velocity of inquiline is: (iii) increased in the presence of the host and (iv) reduced in contact with the internal walls compared with external walls of host nest. The mean time to death of inquiline workers is lower in contact with host (independently from the same or different nest) compared with control and the mean time to death of inquiline workers is lower in contact with external walls of host nest compared with control group and the inner walls. The distance walked and walking velocity of inquiline workers in contact with their hosts (from the same or different nest) did not differ from control, however, these parameters were reduced when workers were in contact with inner and external walls compared with control. In general, our results showed that I. microcerus adopt behavioral strategies to avoid perception by its host.

On the Chemical Disguise of a Physogastric Termitophilous Rove Beetle

Inter-specific symbiotic links are often reinforced by morphological, physiological, or behavioural trait modification undergone by the associated species. In some cases, such as in physogastric termitophile staphylinids, such modifications do facilitate the social interaction. Here we inspect chemical traits of the physogastric staphylinid Corotoca melantho (Insecta: Coleoptera) and its termite host Constrictotermes cyphergaster (Insecta: Blattodea: Isoptera), aiming to verify whether staphylinids resemble their host. First, we compared CHC profiles of hosts and guests within and among termitaria, to gather evidence on the origin of such profiles in guests. Then, we examined nitrogen and carbon isotopic signatures of these cohabitants to inspect whether chemical disguise is achieved by predation of host workers by staphylinids. Beetles presented CHC more similar to the CHC of their cohabiting termites than to (i) their conspecifics and (ii) termites from another nest, thereby favouring the hypothesis on CHC acquisition by guests. Isotopic signatures revealed that such similarities could not be majorly determined by share nutrition between these cohabitants. In general, our results evidenced that chemical disguise in termitophiles may function as a strategy for social integration in morphological mimics.

Biology and defensive secretion of myrmecophilous Thiasophila spp. (Coleoptera: Staphylinidae: Aleocharinae) associated with the Formica rufa species group

ABSTRACTVarious aspects of the biology of the myrmecophilous Thiasophila angulata and T. szujeckii (Staphylinidae; Aleocharinae), mainly associated with the Formica rufa species group, are studied. The composition of defensive gland secretions from adults of T. angulata has been analysed. The complete development (egg-L1-3-pupa-adult form), including adult overwintering, of both species takes place solely in ant nests. Under laboratory conditions, this lasts for about 22 days in T. angulata, and the period elapsing between the old and new generations of insects is approximately two months. The mean fecundity of adults of this species (28 eggs) was determined, as well as the duration of its reproductive period (mean 28.5 days), and lifespan (mean 67 days). In natural conditions T. angulata, found within nests of Formica polyctena and F. rufa, produces three generations, and the sibling species T. szujeckii one generation per year. These two species differ in their phenologies and abundance dynamics of adults and larvae, which is linked to the size and temperature regime of the host nest. The results of this study uphold the recent separation of T. angulata and T. szujeckii based on morphological features of adults and selected molecular markers. Adults and larvae of T. angulata forage on both live and dead food items accumulated by the host, as well as on the host’s eggs and larvae. Both the beetle larvae and adults remain unmolested among the host workers. The adults use their defensive gland secretions, which contains substantial quantities of toxic quinones, when necessary. According to the current categories of myrmecophiles, T. angulata (and by analogy, T. szujeckii as well) should be classified as a species wholly integrated with the host.

Glandular sources of pheromones used to control host workers (Apis mellifera scutellata) by socially parasitic workers of Apis mellifera capensis

Pheromonal control by the honey bee queen is achieved through the use of secretions from diverse glandular sources, but the use of pheromones from a variety of glandular sources by reproductively dominant workers, has not previously been explored. Using the social parasite, Apis mellifera capensis clonal worker we studied the diversity of glandular sources used for pheromonal control of reproductively subordinate A. m. scutellata workers. To determine whether pheromones from different glandular sources are used by reproductively active workers to achieve dominance and evaluate the degree of pheromonal competition between workers of the two sub-species, we housed groups of workers of the two sub-species together in cages and analysed mandibular and tergal gland secretions as well as, ovarian activation status of each worker after 21days. The results showed that A. m. capensis invasive clones used both mandibular and tergal gland secretions to achieve reproductive dominance and suppress ovarian activation in their A. m. scutellata host workers. The reproductively dominant workers (false queens) produced more queen-like pheromones and inhibited ovarian activation in subordinate A. m. scutellata workers. These results show that tergal gland pheromones working in synergy with pheromones from other glands allow individual workers (false queens) to establish reproductive dominance within these social groups and to act in a manner similar to that of queens. Thus suggesting that, the evolution of reproductively dominant individuals (queens or false queens) and subordinate individuals (workers) in social insects like the honey bee is the result of a complex interplay of pheromonal signals from different exocrine glands.

Chemical disguise of myrmecophilous cockroaches and its implications for understanding nestmate recognition mechanisms in leaf-cutting ants.

BackgroundCockroaches of the genus Attaphila regularly occur in leaf-cutting ant colonies. The ants farm a fungus that the cockroaches also appear to feed on. Cockroaches disperse between colonies horizontally (via foraging trails) and vertically (attached to queens on their mating flights). We analysed the chemical strategies used by the cockroaches to integrate into colonies of Atta colombica and Acromyrmex octospinosus. Analysing cockroaches from nests of two host species further allowed us to test the hypothesis that nestmate recognition is based on an asymmetric mechanism. Specifically, we test the U-present nestmate recognition model, which assumes that detection of undesirable cues (non-nestmate specific substances) leads to strong rejection of the cue-bearers, while absence of desirable cues (nestmate-specific substances) does not necessarily trigger aggression.ResultsWe found that nests of Atta and Acromyrmex contained cockroaches of two different and not yet described Attaphila species. The cockroaches share the cuticular chemical substances of their specific host species and copy their host nest’s colony-specific cuticular profile. Indeed, the cockroaches are accepted by nestmate but attacked by non-nestmate ant workers. Cockroaches from Acromyrmex colonies bear a lower concentration of cuticular substances and are less likely to be attacked by non-nestmate ants than cockroaches from Atta colonies.ConclusionsNest-specific recognition of Attaphila cockroaches by host workers in combination with nest-specific cuticular chemical profiles suggest that the cockroaches mimic their host’s recognition labels, either by synthesizing nest-specific substances or by substance transfer from ants. Our finding that the cockroach species with lower concentration of cuticular substances receives less aggression by both host species fully supports the U-present nestmate recognition model. Leaf-cutting ant nestmate recognition is thus asymmetric, responding more strongly to differences than to similarities.Electronic supplementary materialThe online version of this article (doi:10.1186/s12898-016-0089-5) contains supplementary material, which is available to authorized users.

Contrasting Evolutionary Rates between Social and Parasitic Bumblebees for Three Social Effect Genes

Reproductive division of labour, characterizing eusocial insect societies, is predicted to reduce efficacy of selection on genes involved in worker traits as selection will be mainly effective in the reproductive caste. Indirect selection acting through a share of genes due to relatedness might be a weak force. Thus, all being equal, population genetic theory adapted to genes with social effects on fitness predicts a higher polymorphism within and between populations on such genes compared to genes with direct effects on fitness. In order to test this prediction empirically, we use social and non-social bumblebee species, all belonging to the genus Bombus. Non-social bumblebees are social parasites of the social species, invading host nests during an early phase of colony development. The parasitic bee, lacking a worker caste, kills the resident queen and starts reproducing, utilizing the host workers in brood care. Three social-effect genes, foraging (for), salivary gland secretion 3 (sgs3) and vitellogenin (vg), were chosen as well as some control genes to be amplified in two social bumblebee species and in two parasitic (non-social) species. High coverage amplicon re-sequencing was used to determine levels of intra- and inter-specific polymorphism. Social effect genes show contrasting rates of evolution. While vg shows a pattern of slightly positive selection, but no sign of social pleiotropy, sgs3 is expected to be a socially pleiotropic gene. The signature of high intraspecific polymorphism, low divergence and the adaptive fixation of derived alleles, along with its expression pattern, predict a socially pleiotropic effect. By contrast, for shows high levels of conservation between social species, suggesting a role in worker behaviour but also functions in queens. This empirical test of evolutionary theory suggests that social effect genes might also operate in both castes resulting in difficulties to interpret effects on molecular evolution. No general molecular pattern of social effect genes could be detected without taking into account their function in each caste and the direction of selection they experienced. Nevertheless, social effect genes experienced a stronger selection pressure in social than in parasitic species.

Interspecific chemical communication in raids of the robber bee Lestrimelitta limao

Most social bees collect floral resources to obtain proteins and carbohydrates. However, the obligate cleptoparasite stingless bee Lestrimelitta limao, the so-called robber bee, is a rare exception as it collects resources by raiding other stingless bee nests. The mechanisms these bees use to overcome host colony defenses are poorly understood. Many host species retreat inside the nest during L. limao attacks and the signals triggering this behavior require a better understanding. While some researchers have proposed that robber bees release chemical compounds that are responsible for host retreat, others have hypothesized that the observed behavior results from communication among host workers. In order to investigate the role of interspecific signals in raids, we tested the effects of robber bees’ mandibular and labial gland secretions on the behavior of Frieseomelitta varia workers. We combined behavioral assays with chemical and electrophysiological analyses. We found that citral and 9-nonacosene are major mandibular gland compounds and two esters, hexadecyl acetate and 9-hexadecenyl acetate, are major labial gland compounds. These three major compounds elicited electro-physiological responses on host worker antennae. Robber bee labial gland extracts repelled both foragers and guards, while mandibular gland content increased aggression. Our results suggest that interspecific communication plays a role during natural raids and that esters from L. limao labial glands, rather than citral, are more likely to trigger the host retreat. The results add to our knowledge about L. limao chemical communication and help to elucidate the mechanisms involved in their intriguing foraging strategy.

Intraspecific worker parasitism in the common wasp, Vespula vulgaris

Insect societies display a remarkable level of cooperation, but their colonies also represent a valuable resource that can be taken advantage of by genetically unrelated individuals. Indeed, several recent studies have documented cases of intraspecific reproductive parasitism, whereby workers penetrate and lay eggs in unrelated colonies in order to have their brood raised by the host workers. Previously, it has been predicted that queenless colonies should be a prime target of such intraspecific worker parasitism, as in such colonies the parasite workers would be able to reproduce without interference from either the queen or other workers. So far, this prediction has been supported with data from the honeybee, but evidence from other social insect groups is currently lacking. Here we present the first such test in the common wasp, Vespula vulgaris. In particular, workers from queenright colonies left the natal nest at a higher rate than those from queenless colonies. However, contrary to our predictions, drifter workers targeted queenless and queenright colonies equally. Chemical data suggest that this lack of discrimination may be linked to recognition constraints and the lack of volatile signals that reliably indicate the presence or absence of the queen. In addition, in queenright colonies, drifters activated their ovaries at a rate that was ca. five times higher than the natal workers. Overall, our results suggest that also in wasps, workers can gain inclusive fitness by drifting to unrelated nests, even if the chances of successfully reproducing there may be very slim.

A scent shield to survive: identification of the repellent compounds secreted by the male offspring of the cuckoo bumblebee Bombus vestalis

AbstractIn social insects, the high cost of parental investment has promoted the evolution of traits that reduce or avoid care for unrelated offspring. They have evolved a sophisticated recognition system which enables them to reject foreign individuals, and therefore prevent their nest's exploitation by parasites and predators. Nonetheless, many social parasites are able to overcome social insect recognition and parasitize their parental care behaviour by laying their eggs in host nests. Although several studies have already been conducted on the strategies used by social parasites to successfully invade host nests, the strategy used by its offspring to evade host rejection is still poorly understood. In bumblebees, previous investigations indicated that male offspring of Bombus vestalis (Geoffroy) (Hymeno‐ptera: Apidae), the specific obligate social parasite of Bombus terrestris (L.), may use allomones to evade host worker attacks. Following these studies, we performed electrophysiological studies and behavioural experiments to identify the potential repellents. Six compounds elicited electroantennographic responses in host worker antennae. The corresponding mixture of synthetic volatiles as well as pure tetradecyl acetate, and to a lesser extent pure (Z)‐11‐hexadecenyl acetate, showed a repellent effect on starved host workers in a feeding bioassay. We hypothesize that tetradecyl acetate has a key function in the repellent effect of the secretions of B. vestalis male offspring towards B. terrestris host workers.

The placid slavemaker: avoiding detection and conflict as an alternative, peaceful raiding strategy

Host entry is a crucial step in a parasite’s life cycle. When parasites manage to circumvent host detection, exploitation of host resources is facilitated, as host defenses have not to be counteracted. Social parasites exploit animal societies and, likewise, detection avoidance can be beneficial. Yet, due to strong selection pressures, hosts of socially parasitic slavemaking ants often recognize them as enemies, so that slavemakers use open force to raid host colonies. These fights, however, prohibit the enslavement of adult host workers (eudulosis), which cannot be manipulated to work for them. Instead, they steal brood during raids, and enslave those upon emergence. In contrast to the violent raids of most slavemakers, no aggression occurs during most of the raids of the newly described slavemaker Temnothorax pilagens. Thereby, T. pilagens regularly induces adult host workers to be part of their slave workforce. We demonstrate that non-enslaved colonies of its host species respond to this slavemaker with little aggression. We further investigate how the slavemaker circumvents recognition and show that chemical resemblance of host profiles might explain the low aggressive responses. But, which parameters determine whether slave raids escalate, resulting in carnage among defenders? Our experiments reveal that host aggression is counterproductive as aggressive host colonies suffer from more fatalities during raids, but cannot save more brood. The slavemaker, however, benefits from not eliciting fights, as it doubles its enslaved workforce by capturing brood plus adult host workers. Hence, undercutting recognition allows the slavemaker to avoid raid escalation with its associated fitness benefits.

Integration strategies of a leaf-cutting ant social parasite

To enter and integrate into host nests, ant social parasites employ a variety of behavioural and chemical strategies for bypassing host defences. Alternative chemical strategies are often considered separately, because only one is assumed to be effective in each particular species or in specific phases of the usurpation process. We studied the integration process of inquiline social parasite queens of Acromyrmex insinuator into nests of its host, the leaf-cutting ant Acromyrmex echinatior. When transplanted to a new host colony, parasite queens were initially attacked but later accepted by host workers, while non-nestmate host queens were always killed in this process. Parasite queens were more readily accepted by host colonies that already contained a parasite queen. The cuticular chemical profiles of parasite queens appeared to be specific to a host colony and parasite queens had higher amounts of cuticular n-alkanes than host queens, a substance class that is typically not relevant for nestmate recognition. We found evidence for two chemical strategies that are not mutually exclusive: (1) increased n-alkane levels suggest chemical insignificance, i.e. that parasites are able to enter host colonies because crucial recognition labels are absent, and (2) colony specificity of labels and attacks by non-nestmate host workers suggest that camouflage, a gradual acquisition of host colony-specific labels during integration, applies as well. We argue that combining insignificance and camouflage may be synergistically adaptive for intruding inquiline queens when this leads to a higher likelihood of achieving permanent acceptance.

How to escape from the host nest: Imperfect chemical mimicry in eucharitid parasitoids and exploitation of the ants’ hygienic behavior

Communication in ants is based to a great extent on chemical compounds. Recognition of intruders is primarily based on cuticular hydrocarbon (CHC) profile matching but is prone to being cheated. Eucharitid wasps are specific parasitoids of the brood of ants; the immature stages are either well integrated within the colony or are protected within the host cocoons, whereas adult wasps at emergence must leave their host nest to reproduce and need to circumvent the ant recognition system to escape unscathed. The behavioral interactions between eucharitid wasps and workers of their host, the Neotropical ant Ectatomma tuberculatum, are characterized. In experimental bioassays, newly emerged parasitoids were not violently aggressed. They remained still and were grabbed by ants upon contact and transported outside the nest; host workers were even observed struggling to reject them. Parasitoids were removed from the nest within five minutes, and most were unharmed, although two wasps (out of 30) were killed during the interaction with the ants. We analyzed the CHCs of the ant and its two parasitoids, Dilocantha lachaudii and Isomerala coronata, and found that although wasps shared all of their compounds with the ants, each wasp species had typical blends and hydrocarbon abundance was also species specific. Furthermore, the wasps had relatively few CHCs compared to E. tuberculatum (22–44% of the host components), and these were present in low amounts. Wasps, only partially mimicking the host CHC profile, were immediately recognized as alien and actively removed from the nest by the ants. Hexane-washed wasps were also transported to the refuse piles, but only after being thoroughly inspected and after most of the workers had initially ignored them. Being recognized as intruder may be to the parasitoids’ advantage, allowing them to quickly leave the natal nest, and therefore enhancing the fitness of these very short lived parasitoids. We suggest that eucharitids take advantage of the hygienic behavior of ants to quickly escape from their host nests.

Degenerate slave‐makers, but nevertheless slave‐makers? Host worker relatedness in the ant Myrmoxenus kraussei

Socially parasitic ants of the formicoxenine genus Myrmoxenus exhibit considerable diversity in colony structure and life history. While some species are active slave-makers with many workers and others are workerless 'murder-parasites,' Myrmoxenus kraussei is considered as a 'degenerate slave-maker' because of its very low worker numbers. Here, we document that Temnothorax recedens host workers in single colonies of M. kraussei from Lago di Garda, Italy, exhibit significantly more genetic diversity than workers in unparasitized colonies. This raises the possibility that, despite its low worker numbers, M. kraussei may actively engage in slave raids in nature.