Showing papers in "Insectes Sociaux in 2018"

The gut microbiome is associated with behavioural task in honey bees

Abstract: The gut microbiome is recognised as playing an integral role in the health and ecology of a wide variety of animal taxa. However, the relationship between social behavioural traits and the microbial community has received little attention. Honey bees are highly social and the workers perform different behavioural tasks in the colony that cause them to be exposed to different local environments. Here we examined whether the gut microbial community composition of worker honey bees is associated with the behavioural tasks they perform, and therefore also the local environment they are exposed to. We set up five observation hives, in which all workers were matched in age and observed the behaviour of marked bees in each colony over 4 days. The gut bacterial communities of bees seen performing predominantly foraging or predominantly in nest tasks were then characterised and compared based on amplicon sequencing of the 16S rRNA gene. Our results show that some core members of the unique honey bee gut bacterial community are represented in different relative abundances in bees performing different behavioural tasks. The differentially represented bacterial taxa include some thought to be important in carbohydrate metabolism and transport, and also linked to bee health. The results suggest an influence of task-related local environment exposure and diet on the honey bee gut microbial community and identify focal core taxa for further functional analyses.

Recent advances in reproductive biology of stingless bees

Abstract: The reproductive biology of stingless bees is poorly understood, especially when compared to other groups of social bees with great ecological and economic importance. However, research on this topic has grown over the past few years, mostly driven by technological advances in molecular biology. Here, we aimed to review several recent developments in the research of stingless bee reproduction, including the mating systems of stingless bees, reproductive strategies of queens, inbreeding and diploid male production, as well as conflicts over male production. We also briefly explore topics that have not substantially advanced, highlighting the gaps that need to be further investigated. Understanding the reproductive biology of stingless bees can aid conservation efforts for these important pollinators and improve management practices that promote their sustainable economic use.

Using T- and Y-mazes in myrmecology and elsewhere: a practical guide

Abstract: T- and Y-mazes are powerful tools for studying the behavioural ecology and cognition of animals, especially ants. Such mazes are cheap, easy to deploy, and very flexible, allowing diverse subjects to be studied. These include cue and route learning, pheromone following, and testing for cognitive abilities such as associative and concept learning. However, while simple, the use of bifurcation mazes has many pitfalls, especially for ants which deposit pheromone trails. In this methods primer, I discuss the strengths and limitations of using bifurcation mazes to study ant behaviour, and outline some of the pitfalls to be avoided. I also provide a description of a suggested Y-maze design, and methodological details about using Y-mazes to study associative learning, route learning, and trail pheromone following. Although the description of the uses of bifurcation mazes, and their pitfalls, is not exhaustive, this methods primer hopes to be of use to both beginners and more experienced researchers in designing and deploying bifurcation mazes in their research. While primarily aimed at myrmecologists, much of the content of this methods primer will be broadly applicable to animal behavioural research.

Detection of honey bee viruses in Argentinian stingless bees (Hymenoptera: Apidae)

Abstract: The Meliponini is a eusocial group of bees tropically distributed. In Argentina, 37 species have been recorded, mostly in Misiones province. They use a great variety of sites to build their nests including tree hollows, cavities formed in rocks, human constructions or underground spaces. Numerous natural enemies are associated with stingless bees, including viruses. Until now, some viruses present in honey bees and related to the colony collapse disorder (CCD), have been found in several wild bees around the world. Here, we have studied the presence of honey bee viruses in stingless bees from different locations of Misiones province, Argentina. On this research, 73 samples of ten workers belonging to 12 species of stingless bees and feral honey bees, have been analyzed. Our results confirm the presence of three viruses: ABPV, IAPV and DWV Type A in four species of stingless bees and feral honey bees. More studies are required to establish if ABPV, IAPV and DWV are natural pathogens of stingless bees that have been spilled over to honey bees, or were transmitted by Apis mellifera to stingless bees.

Genomic footprint of evolution of eusociality in bees: floral food use and CYPome “blooms”

Abstract: Comparative analyses of genomes of ten bee species representing different degrees of social complexity have demonstrated that independent transitions to eusociality are often accompanied by or lead to expansions or contractions of gene families (albeit different families across independent lineages). Because collective gathering, processing, and storage of plant products is a hallmark of bee social complexity, we examined the genomic inventory of cytochrome P450 genes (the CYPome) in these ten genomes, to search for footprints of eusociality in phytochemical detoxification pathways and, using a Bayesian implementation of the McDonald–Kreitman test, evidence of adaptive evolution within P450 lineages associated with food processing in eusocial florivorous Bombus and Apis species versus eusocial carnivorous Polistes species.We found no patterns linking CYPome size to level of social complexity within the ten bee genomes at the gene family level; however, a pattern emerged at the subfamily level, with the CYP6AS subfamily most diverse in perennial eusocial resin-collecting bees. In Apis mellifera, several CYP6AS enzymes are known to metabolize flavonols, ubiquitous constituents of nectar and honey, pollen and beebread, and resins and propolis. CYP6AS subfamily size varies from 7 in the solitary Habropoda laboriosa and the facultatively eusocial Lasioglossum albipes to 17 in the perennial eusocial Melipona quadrifasciatus; the degree of sociality across the ten species is correlated with CYP6AS inventory size (Spearman’s rho = 0.704, p < 0.023). Remarkably, there is perfect overlap between CYP6AS genes upregulated by the flavonol quercetin in A. mellifera and CYP6AS genes with signs of adaptive evolution in either Apis or Bombus. Our finding of positive selection on CYP6AS genes in Apis and Bombus, but not Polistes supports the hypothesis that CYP6AS subfamily expansion was involved in facilitating the shift from carnivory to florivory in bees. That some CYP6AS enzymes metabolize flavonoids suggests that subfamily expansion results from increased evolutionary exposure to these phytochemicals, through concentration of nectar into honey, pollen into beebread, and plant resins into propolis. Accompanying the evolutionary progression from solitary to perennial eusocial behavior in bees is a transition from short-term storage of ephemeral low-quality resources to concentrating and stockpiling those resources for colony use, with a concomitant need for phytochemical detoxification.

Nesting characteristics, floral resources, and foraging activity of Trigona iridipennis Smith in Bankura district of West Bengal, India

Abstract: For successful establishment of meliponiculture with Trigona iridipennis Smith, several attributes such as nesting substrates, orientations, elevation, internal characteristics of nests, floral resources, and foraging activity were studied in Bankura district of West Bengal, India. The most commonly found nesting substrate was tree trunks, especially within the cavities in tree trunks of Butea monosperma. Majority of the wild nests were oriented westward direction with an elevation of > 2–≤ 3 m from the ground level. The mean cavity size was 204.3 ± 92.45 × 159 ± 17.59 × 174.5 ± 26.13 mm3. The diversified local angiosperm flora supports the broad polylectic foraging habit of the bee species. Most of the visited plants were of tree habits and had small-sized flowers with yellow, white, and cream colours. The best represented families were Fabaceae and Asteraceae. The plants intensely utilized by the bee species were Acacia auriculiformis, Borassus flabellifer, Brassica nigra, Eucalyptus globulus, and Lannea coromandelica. In contrast to majority of multifloral honey samples, all the pollen loads were unifloral which reflects the high degree of floral fidelity behaviour of the bee species. The foraging activity of the bee species varied according to time hours, plant species, weather conditions, and seasons. It was confined to daytime from 5.00 to 18.00 h, reaching its zenith during 9.00–11.00 h and 15.00–1600 h. Maximum activity was observed in spring, followed by winter, late autumn, summer, autumn, and monsoon. Mean number of foragers without pollen load and resin load was much higher than pollen foragers and resin foragers.

The distribution of thelytoky, arrhenotoky and androgenesis among castes in the eusocial Hymenoptera

Abstract: Thelytokous parthenogenesis is the production of females from unfertilized eggs. In this review we categorize the known thelytokous eusocial Hymenopterans (mostly ants) by their modes of worker and queen reproduction. The resultant tabulation reveals that: (1) there are no species in which queens are thelytokous and workers are exclusively arrhenotokous (asexual production of males). (2) When workers are capable of thelytoky, there are no examples of species in which queens are strictly thelytokous. (3) Strict queen thelytoky is only present in species with irreversibly sterile workers. (4) Facultative queen thelytoky and sterile workers can lead to the evolution of androgenesis (males are clonal sons of their fathers). These associations are probably best explained by consideration of differing fitness benefits of thelytoky between workers and queens and suggest that some combinations are unlikely to evolve. We therefore predict that they will hold for all eusocial Hymenoptera. No examples of endobacterium-induced thelytoky are known for the eusocial Hymenoptera, whereas endobacterium-induced thelytoky is widespread in the solitary Hymenoptera. We argue that this is because species in which both queens and workers are thelytokous that are unlikely to persist over evolutionary time. Further, eusocial species have single-locus sex determination, which is not compatible with endobacterium-induced feminization that is typically based on genome duplication. Only two thelytokous eusocial bees are known, and their modes of reproduction are consistent with the associations seen in ants. Thus far, no thelytokous eusocial wasps have been identified.

Working in the rain? Why leaf-cutting ants stop foraging when it’s raining

Abstract: Understanding how environmental factors modulate foraging is key to recognizing the adaptive value of animal behavior, especially in ectothermic organisms such as ants. We experimentally analyzed the effect of rain on the foraging of leaf-cutting ants, a key ant group that is commonly found in rainy habitats. Specifically, we experimentally discriminate among direct and indirect effects of rain on laden ants and explore whether ants respond to rain predictors by incrementing their speed. Watered loads were frequently dropped although ants were not wet, and watered ants also dropped their loads although loads were not wet. Watered leaf fragments increased their weight by 143% and were dropped independently with regards to area or symmetry. Watering the trail did not affect the proportion of ants that dropped their loads. Ants increased their speed by 30% after experimental increments in relative humidity and the noise of raindrops on leaves near the trail. Our experimental results confirm earlier anecdotic evidence of the negative effect of rainfall on the foraging of leaf-cutting ants. We demonstrate that rain can strongly limit ant foraging through different mechanisms, affecting both the ant itself, and the maneuverability of laden ants, by increasing the weight of their loads. We also depict behavioral responses that may mitigate this negative effect on foraging: walking faster at signals of rainfall to reduce the portion of leaf fragments lost. Our results illustrate how environmental factors can directly and indirectly constrain ant foraging and highlight the relevance of behavioral responses to mitigate these effects.

How do animals find their way back home? A brief overview of homing behavior with special reference to social Hymenoptera

Abstract: Performing efficient homing, ie, returning to a previously known place, is crucial for the survival of any motile animal Animals perform homing across different spatial scales and environments, employing various mechanisms with the aid of different sensorimotor systems molded by their varied evolutionary histories and ecological constraints Despite these differences, most of the homing mechanisms across different taxa can be explained by some general basic mechanisms Studies from social hymenopterans contribute substantially to the knowledge base of this study field and are, especially, interesting—they show excellent homing capabilities while possessing relatively simple neural architectures, and hence, their homing mechanisms are considered as economic solutions to a complex problem Moreover, many of their homing mechanisms have also been observed in other taxa including vertebrates With the advent of new technologies and increased research, our understanding of the hymenopteran homing is improving faster than ever—and therefore, a regular contemporary update might be of much help In this review, I present a brief synthesis of previous and current understanding of homing mechanisms in social hymenopterans, with descriptions of the cues that they exploit for homing, and a comparative discussion on terminologies frequently used in social Hymenoptera with analogous terminologies used to describe similar phenomena in other taxa I conclude with a note on the potential of applying the knowledge from homing studies in other fields of research like neurobiology and robotics, and possible future directions

Queen traits and colony size of four bumblebee species of China

Abstract: Bumblebee pollination efficiency is significantly affected by colony size, which differs among different bumblebee species. Bumblebee colonies are initiated by a single queen; thus queen traits have an important influence on colony development. To make better use of native bumblebee species and select bumblebee species for commercial rearing, queens from four bumblebee species in China, Bombus terrestris, B. lantschouensis, B. patagiatus and B. ignitus, were reared and studied to determine whether differences in queen traits and colony size occur at the interspecific level. In our study, the four bumblebee species differed significantly in colony size, queen body length, spermatheca size and sperm quantity. The queens of the four species mated only once. Among these four bumblebee species, the species with more sperm in the queen’s spermatheca usually exhibited a larger colony size. The quantity of sperm in the queen’s spermatheca might serve as an indicator for selecting bumblebee species with commercial rearing potential. However, our study involved only four bumblebee species; more bumblebee species are needed to confirm the correlation between queen sperm quantity and colony size.

The membrane phospholipid composition of honeybee ( Apis mellifera ) workers reflects their nutrition, fertility, and vitellogenin stores

Abstract: Pollen feeding in the honeybee (Apis mellifera) is dependent on the caste, ethotype, and dominance status of individuals. Pollen is the near-exclusive external source of lipids for the colony. Lipids from pollen are rich in polyunsaturated fatty acyl residues, which, because of their sensitivity to lipid peroxidation, have been suggested to limit the lifespan of individual bees. We here investigated whether the spectrum of phosphatidylcholine (PC), the main class of membrane-constituting lipids in insects, is indeed, connected to pollen feeding. We further studied the relationship between pollen feeding, PC spectra, and fat-body stores of vitellogenin, an indicator of potential longevity in bees. For this, we determined the pollen consumption, PC spectra, abdominal vitellogenin stores, and behavioral as well as reproductive status of individuals in queenless groups of workers. In contrast to earlier studies, we found that reproduction in workers is not universally linked to trophallactic dominance alone, but can be accompanied by strong pollen consumption. Pollen consumption seemed connected to a strong remodeling of tissue PC spectra. There was no systematic link between these spectra and trophallactic activity, but individuals with strongly deviating spectra also showed extreme behavioral profiles. Abdominal vitellogenin was strongly and positively linked to pollen-influenced PC spectra and the prevalence of polyunsaturated fatty acyl residues, contradicting the hypothesis that pollen consumption is systematically leading to a shorter lifespan in workers. Our results suggest that the association between pollen consumption, short lifespan, and functional sterility that differentiates workers from queens cannot in all cases be extended to the situation within the worker caste.

Social and private information influence the decision making of Australian meat ants (Iridomyrmex purpureus)

Abstract: For social animals, decision-making is influenced by both social information provided by the group, and private information based on the individual’s personal experience. Social insects make excellent study systems for understanding how social and private information is used by individuals to influence their navigational route choice, and thereby influence the collective decision-making strategy of the group. Using colonies of the Australian meat ant, Iridomyrmex purpureus, we demonstrate that when individual workers are trained to a rewarding arm in a Y maze, the trained ants use private information (memory) in route choice when social information (trail pheromone) is experimentally removed and have no preference when private information and social information are in direct conflict with each other. Additional experience did not provide a strong training effect, such that ants returning after their first training trip tended to choose the path they had been trained on (private information) and subsequent trips did not have a significant additional effect on this initial preference.

Do mutualistic associations have broader host ranges than neutral or antagonistic associations? A test using myrmecophiles as model organisms

Abstract: Symbiotic associations are found across all kingdoms of life and are integral to ecosystem structure and function. Central to understanding the ecology and evolution of symbiotic relationships is an understanding of what influences host range; the number of host species that a symbiont can utilize. Despite the importance of host breadth among symbionts, relatively little is known about how the relationship that a symbiont has with its host influences its host range. Additionally, contrasts among interaction types often involve diverse groups of unrelated host species. To test how host range varied with interaction type, we used a global synthesis of over 1600 species of myrmecophiles, those organisms that have symbiotic associations with ants. We used an indexed literature search to collate known myrmecophile species and their hosts, and to determine how two degrees of dependence (facultative, obligate) and four types of relationships (mutualism, commensalism, kleptoparasitism, and parasitism) among myrmecophiles and their hosts influence host range. Our synthesis showed that, overall, myrmecophiles exhibited a high degree of host specialization, and facultatively dependent myrmecophiles had broader host ranges than those with obligate interactions. Myrmecophiles with mutualistic relationships had broader host ranges than neutral or antagonistic relationships. Additionally, lepidopteran myrmecophiles exhibited broader host range patterns than other taxa. Our results have important implications for how symbiotic associations are understood, with positive relationships (mutualisms) associated with broader host range, and antagonistic relationships (parasitism) associated with narrow host range.

Testing for aggression and nestmate recognition in the Eastern subterranean termite (Reticulitermes flavipes)

Abstract: Social insect colonies typically have well-defined social and physical boundaries but in some cases, colonies may take-on a more diffuse form with no obvious nestmate recognition or inter-colony aggression. Why colonies adopt closed versus open societies is not well understood, but it is presumably related to the genetic or environmental identity of individuals. In this study, we use Canadian populations of the Eastern subterranean termite (Reticulitermes flavipes) to test for evidence of aggression and nestmate recognition. Specifically, we predict that any inter-colony aggression will increase as a function of geographic distance. In short-term, (5-min) Petri-dish trials (varying caste, group size and colony source) we observed no evidence of aggression. However, in 2- and 7-day shared-resource assays, we observed very little inter-colony mixing and a high incidence of mortality in non-nestmate pairings. Our long-term observations imply that subterranean termites sort and potentially compete on the basis of nest origin, and that this recognition is mediated in part by ecological context. This behavior would not be evident from Petri dish-style assays, which lack this context and may explain why prior studies of kin or nestmate recognition in R. flavipes have yielded mixed results.

Contrasting termite diversity and assemblages on granitic and basaltic African savanna landscapes

Abstract: Termites are recognised soil ecosystem engineers in the tropics and sub-tropics, making the understanding of their distribution a priority However, there is a poor understanding of how differences in soil properties and plant biomass productivity affect termite species diversity We compared the diversity of termites between two soils of differing geological provenance (basalt and granite), and consequently contrasting nutrient content, but subject to similar climatic conditions in a semi-arid Zimbabwean savanna Basaltic soils contained more dead wood, and were more nutrient-rich than granitic soils, with significantly higher exchangeable Ca and Mg, and available P, and a less acidic pH However, despite this higher soil nutrient status on basalts, functional and taxonomic termite diversity was higher on granites, although termite abundance was similar between the geological formations Termite assemblages differed between the geological formations, with very little overlap We conclude that termite diversity is highly influenced by soil productivity, with nutrient-poor soils having higher diversity, potentially due to reduced competitive exclusion or differences in species adaptation to soil conditions

Allee effect in termite colony formation: influence of alate density and flight timing on pairing success and survivorship

Abstract: The Allee effect is a positive relationship between any component of individual fitness and the density of conspecifics. Theoretical models predict that monogamy, where males and females are constrained from having multiple mates, is more susceptible to the Allee effect. In most termite species, including Reticulitermes spp., found new colonies by monogamous pairs (i.e., primary king and queen); however, little is known about the effects of alate density and flight timing on pairing and colony foundation success. In this study, a positive relationship between alate density and pairing success was observed in the subterranean termite, Reticulitermes speratus. Upon release of dealates (individuals after shedding wings) every 3 days for 9 days at 10, 20, 40, or 80 pairs/m2/day in a semi-natural field, no pairs were observed for the 10 pairs/m2/day treatment after 3 months. However, 7.5, 13.8, and 18.1% of dealates formed pairs in the 20, 40, and 80 pairs/m2/day groups, respectively. Most pairs (78.7%) comprised dealates released simultaneously, and 17.3 and 4% comprised dealates released 3 and 6 days apart, respectively. R. speratus also preferred brown rotten pine for colony foundations to white rotten oak. This study provides important new insights into the density effects and nest-site preference for termite colony foundation.

Cuticular hydrocarbons determine sex, caste, and nest membership in each of four species of yellowjackets (Hymenoptera: Vespidae)

Abstract: Cuticular hydrocarbons (CHCs) of social insects have typically been studied for their roles in reproductive signaling (i.e., fertility) rather than sexual signaling (i.e., interest in mating), resulting in little information about CHCs of males and virgin females. This dearth of information applies particularly to social wasps. We tested the hypothesis that CHCs differentiate sex, caste, and nest membership in each of four yellowjacket species (baldfaced hornets, Dolichovespula maculata; southern yellowjackets, Vespula squamosa; western yellowjackets, V. pensylvanica; V. alascensis). Cold-euthanized queens (21), gynes (81), workers (125), and males (77) from 35 nests were extracted with pentane, and each of the resulting 304 extracts was analyzed by gas chromatography (GC) and GC–mass spectrometry to identify and quantify CHC constituents (aliphatic alkanes and alkenes; mono-, di-, and tri-methyl-branched alkanes). To determine whether caste and sex differ in CHC profiles of wasps, linear discriminant analyses were performed, using Z-transformed relative CHC peak areas as predictor variables and sex and caste, or nest, as grouping variables. When caste and sex were used as a grouping variable, plots of the first two discriminant functions revealed that wasps from each of the four species clustered into their respective groups (queens, gynes, workers, males), with significant differences in group centroids, as measured by Wilks’ lambda. When nest was used as a grouping variable, plots of the first two discriminant functions revealed that workers from each of the four species and males from each of three species (insufficient sample size for V. pensylvanica) clustered according to nest. Diagnostic power calculations show greater inter-caste than inter-nest variation. Our data support the above hypothesis and inspire future studies to determine the definitive role(s) that gyne- and male-specific CHCs play in the context of sexual communication, from the perspective of both males and females.

Linear dominance hierarchies and conditional reproductive strategies in a facultatively social carpenter bee

Abstract: In social groups, dominance rank may have important fitness consequences, as higher ranking individuals tend to have higher overall fitness. In social nests of the eastern carpenter bee, Xylocopa virginica, females in social nests demonstrate a complete division of labour where one female is the dominant egg layer and forager while other females in the nest are non-reproductive. We investigated the nature of reproductive queues in this species by performing removal experiments across 3 years to observe how females respond to new reproductive opportunities in the nest. When a primary female was removed, a secondary female always assumed her position as replacement primary and reproductive queues formed in a linear fashion. A third type of female in the nest, the tertiary female, did not become reproductive, even if she was the only female remaining. In delaying reproduction, tertiary females were able to overwinter a second time and were often successful at becoming reproductive in their second summer. Tertiary females were smaller than primary or secondary females, had higher fat stores and lower ovarian development. When all other females in the nest were removed, tertiary females were observed ejecting the offspring of previous dominant females in the nest. Tertiary females appear to represent a novel reproductive strategy among the Hymenoptera who can drastically alter their physiology and behaviour, essentially doubling their life span to maximize reproductive potential.

Insights into the biodiversity and causes of distribution of potential entomopathogens associated with leaf-cutting ants

Abstract: To our knowledge, this work is the first large-scaled, systematic survey of potential entomopathogens associated with worker ants of several Acromyrmex species. The study was performed at nine sites located in five Phytogeographical Provinces across Argentina. We recorded 28 species of fungi with entomopathogenic behaviour, which infected 24.3% of the 4737 collected ants from 94 colonies. Fusarium oxysporum and F. solani were the most widely distributed, followed by Purpureocillium lilacinum and Beauveria bassiana. The occurrence of species across nests within the same site varied from null to 98%. We did not detect any systematic association between fungi and site, Phytogeographical Province or ant species. Instead the microhabitats that surround each nest appear to play an important role in defining entomopathogen communities. We found that climatic variables like maximum temperature, dew point, and relative humidity helped to account for the distribution of these fungi at the site scale. Besides, colonies from undisturbed sites showed higher abundance of infections with entomopathogens than those from disturbed ones. These results greatly improve the knowledge of the ecology of the filamentous fungi associated with leaf-cutting ants. In addition, we proposed that the combination of the entomopathogen virulence and the resistance of ant colonies may be an important but overlooked effect influencing the diversity of entomopathogens.

Underground nest building: the effect of CO2 on digging rates, soil transport and choice of a digging site in leaf-cutting ants

Abstract: By reacting to local environmental stimuli, ant workers excavate a nest that offers suitable climatic conditions. Workers may face increasing CO2 levels while digging across the soil profile, and it is an open question whether these levels are used as cues during nest excavation. Here, we explored the influence of different underground CO2 concentrations on digging behavior in the leaf-cutting ant Acromyrmex lundii. We first quantified digging rates and transport of excavated material as a function of CO2 levels, ranging from atmospheric values to 11% CO2. The mass of both the excavated soil and the pellets transported out of the digging chamber were quantified. CO2 preferences for excavation were investigated in a second experiment, in which workers were presented with a choice of two digging sites that differed in their CO2 levels, ranging from atmospheric to 4% CO2, and the mass of excavated material was quantified. Digging rates were similar for all tested CO2 levels up to 7%, and only significantly lower for 11%. The transport of excavated soil increased with increasing CO2 levels up to 7%, and then decreased at 11%. Workers preferred digging at 1% CO2 and avoided levels of 4%. We suggest that the observed CO2 preferences are likely driven by the requirements of their symbiotic fungus, and could be one of the reasons why colonies of A. lundii excavate superficial nest chambers.

Occupation of wood warbler Phylloscopus sibilatrix nests by Myrmica and Lasius ants

Abstract: Bird nests can provide habitats for various invertebrates, including ectoparasites, scavengers, and predators. Records of ants associating with active bird nests mostly involve the insects searching for food, with some exceptional records of ants raising their broods (eggs, larvae or pupae) within songbird nests in nest-boxes or tree cavities. We present data for a previously undocumented, but apparently regular, occurrence of ants and their broods within the active nests of a songbird, the wood warbler Phylloscopus sibilatrix (Bechstein, 1793), which builds domed nests on the ground in European forests. Systematic recording found ants, mostly Myrmica ruginodis Nylander, 1846, in 43% of 80 wood warbler nests in the primary forest of Bialowieza National Park (Poland) during the springs of 2016–2017, including ant broods in 30%. Ad hoc records from this site in 2004–2015 found ants in a further 29% of 163 nests, including broods in 20%, indicating a regular association. However, examination of 37 nests from secondary forest in Switzerland and Great Britain founds ants in only 14%, and broods in just 5%. We discuss the potential drivers and mechanisms of the observed association between breeding wood warblers and ants, including the apparent difference in frequency between the primary and secondary forests.

Climatic variation across a latitudinal gradient affect phenology and group size, but not social complexity in small carpenter bees

Abstract: Greater social complexity at lower latitudes has been observed in a variety of arthropods from termites to spiders. Social behavior in the small carpenter bees, Ceratina, has been shown to vary widely both between species and across geographic range. Our goal was to determine how social plasticity of three populations of Ceratina species, C. calcarata and C. strenua, vary across a latitudinal gradient. The longer rearing season in the south did not result in two separate brood rearing periods, but instead increased brood production of a single brood with a higher female sex bias. The social structure of nests remained stable across both species’ ranges: mothers exhibit prolonged parental care and worker dwarf eldest daughters occur among populations and species. This is the first report of worker daughters in C. strenua. The ubiquity of worker daughter production in eastern North American Ceratina suggests that factors outside of climate underlie the early division of labor between the reproductive mother and worker dwarf eldest daughter.

Day/night upper thermal limits differ within Ectatomma ruidum ant colonies

Abstract: In the tropics, daily temperature fluctuations can pose physiological challenges for ectothermic organisms, and upper thermal limits may affect foraging activity over the course of the day. Variation in upper thermal limits can occur among and within species, and for social insects such as ants, within colonies. Within colonies, upper thermal limits may differ among individuals or change for an individual throughout the day. Daytime foragers of the Neotropical ant Ectatomma ruidum have higher critical thermal maxima (CTmax) than nocturnal foragers, but whether these differences occur among or within colonies was not previously known. We investigated the potential mechanisms accounting for day/night variation in CTmax of E. ruidum foragers by testing whether CTmax varied among or within colonies or due to individuals within colonies acclimating to changes in temperature over a short time scale (3 h). We found within- but not among-colony differences in CTmax on a diel cycle, and we found no evidence for among- or within-colony partitioning of foraging times by individual workers. Individuals did not acclimate to experimental manipulations of temperature, although additional experiments with more ecologically relevant temperature manipulations are needed to rule out this mechanism. In summary, we have shown that day/night differences in upper thermal limits can occur within ant colonies, but further investigation is needed to elucidate the mechanisms driving this variation.

Effect of the presence of brood on the behavior and nutrient levels of emerging individuals in field colonies of Polistes metricus

Abstract: Caste determination in social insects with morphologically distinct castes occurs during a critical period during the larval stage. In contrast, in social insects without morphologically distinct castes the time of eclosion can act as an additional critical period. A number of cues have been identified that influence caste differentiation in social insects but to date, most of the studies have used physiological correlates to determine the effects of these cues on caste determination. Few studies have measured behavioral differences in a natural setting. In this field study, the behavioral and nutritional profiles of individuals of the paper wasp Polistes metricus emerging on nests with and without larvae were determined and compared to emerging workers and gynes from unmanipulated colonies. Based on previous studies, it was predicted that individuals eclosing on nests with larvae would have similar profiles to workers and those eclosing on nests without larvae would have similar profiles to gynes. Individuals that emerged on colonies with larvae had similar behavioral and nutritional profiles to workers as expected. Individuals that emerged on nests without larvae had behavioral and nutritional profiles that were in between workers and gynes and showed signs of active reproduction and nest construction. The results of this study were combined with those of other studies into a model that proposes that there are three thresholds, one in response to photoperiod, one during the larval stage, and one during eclosion that determines if individuals will be workers, active reproducers, or overwintering gynes. This model provides a more complete picture of caste determination in Polistes.

Army imposters: diversification of army ant-mimicking beetles with their Eciton hosts.

Abstract: Colonies of neotropical army ants of the genus Eciton Latreille offer some of the most captivating examples of intricate interactions between species, with hundreds of associated species already described in colonies of Eciton burchellii Westwood. Among this plethora of species found with Eciton colonies, two genera of staphylinid beetles, Ecitomorpha Wasmann, and Ecitophya Wasmann, have evolved to mimic the appearance and parallel the colouration of the most abundant ant worker cast. Here, we study for the first time the association of these ant-mimicking beetles with their ant host in an evolutionary and population genetics framework. The central emphasis is on colonies of E. burchellii, the only Eciton species that harbours both genera of ant-mimicking beetles. Phylogenetic and population structure analyses using the same mtDNA COI region (802 bp) for ants and beetles indicated that speciation patterns of the myrmecophiles were congruent with specialization to a particular Eciton (sub)species. Therefore, current taxonomic treatments of Eciton and its Ecitomorpha and Ecitophya associates need revision. Molecular clock analyses suggested that diversification of the Eciton hosts pre-date that of their guests, with a possible earlier association of Ecitophya (found with a large number of Eciton species) than with Ecitomorpha (found only with E. burchellii colonies). Population-level analyses revealed that patterns of diversification for the myrmecophiles are also consistent with specialisation to a particular host across broad geographical areas but not at small geographical scales, with gene flow within each species found between host colonies, even across landscape features that are strong barriers for Eciton female-mediated gene flow.

Investigating queen influence on worker behaviour using comparisons of queenless and queenright workers

Abstract: Female eusocial sweat bees are capable of behaving as queens or workers. Relatively few females become queens, and those that do can directly manipulate the reproductive behaviour of other females in the nest. We collected Lasioglossum (Dialictus) laevissimum workers from nests with and without queens (queenright and queenless nests, respectively) to investigate the influence queens exert on worker behaviour via direct manipulation. Overall, very few L. laevissimum workers (17%) had developed ovaries in Ontario, but queenright and queenless workers were equally likely to have developed ovaries and worn mandibles. However, queenless workers were more likely to be mated than queenright workers. These results suggest first, that queens inhibit egg-laying in most, but not all workers, and second, that queen behaviour during the first few days of workers’ adult lives exerts a lasting influence on worker behaviour. We also compared social traits of L. laevissimum and other Dialictus species using principal components analysis. A strong correlation between worker reproduction and male availability suggests that queen manipulation of the worker brood sex ratio has evolved as an indirect mechanism for queens to discourage worker reproduction.

Effects of social organization and resource availability on brood parasitism in the facultatively social nocturnal bee Megalopta genalis

Abstract: Understanding the ecological benefits that may select for the evolution of living in groups rather than solitarily is key to understanding the evolution of social cooperation. Defense against natural enemies, such as parasites and predators, is generally acknowledged to be such a benefit, but most studies focus only on predators. Among the bees, parasitism is a major source of brood mortality. Here we use the nocturnal, Neotropical, facultatively social bee Megalopta genalis (Halictidae) to directly compare parasitism rates between social and solitary nests at the same site during times of high and low resource availability. We focus on four parasites: one that eats some pollen but does not kill host offspring [the fly Fiebrigella sp (Chloropidae)] and three that kill host offspring (the beetle Macrosiagon gracilis (Rhipiphoridae), the wasp Lophostigma cincta (Mutillidae), and the congeneric bee M. Noctoraptor byroni). We found no difference in parasitism between social and solitary nests for the four parasites tested. Across all nests, 25–31% of brood cells were parasitized by Lophostigma sp., with parasitism increasing from the dry to wet season, although this seasonal effect was significant only for social nests. Only ~ 4% of brood cells were parasitized by one of the other three parasites, and M. byroni was only found in social host nests. Our data reveal that Megalopta have low rates of parasitism overall, and that this is not a function of social organization or resource availability. Limited nocturnal foraging time and foraging offset from the activity patterns of diurnal parasites may instead play a larger role in keeping parasitism rates low.

Dispersal and mating strategies in two neotropical soil-feeding termites, Embiratermes neotenicus and Silvestritermes minutus (Termitidae, Syntermitinae)

Abstract: Colony breeding systems and dispersal strategies of eusocial insects shape the genetic structure at the colony, but also at the population level. Most of the few molecular studies dedicated to termites suggest that winged reproductives disperse far enough to secure the formation of outbred founding pairs. However, these studies almost exclusively focused on wood-feeding termites and knowledge about the dispersal potential of winged reproductives is missing for soil-feeding termites. We investigated the dispersal and mating strategies of Embiratermes neotenicus and Silvestritermes minutus (Termitidae, Syntermitinae), two very abundant soil-feeding species from the Neotropics. In both species, analysis of microsatellite markers indicated low genetic similarity between closely located colonies and low genetic differentiation between populations separated by less than 10 km. Each of the 39 E. neotenicus colonies originated from a single pair of primary reproductives and the mean inbreeding coefficient of sterile castes was only slightly different from that expected in offspring of an outbred pair. Most S. minutus colonies (34/41) were consistent with outbred biparental foundation. In three mature colonies, the genotypes of sterile castes suggested their origin by mixing of multiple related reproductives. Finally, four colonies in late stage of the colony life cycle contained sterile populations originating from multiple unrelated reproductives. We conclude that long-distance flights resulting in outbred reproduction are common in these soil-feeding species in pristine habitats but that other factors, such as mating preferences, could increase relatedness between founders.

Characteristics of dispersal flight and disperser production in an Asian dry-wood termite, Neotermes koshunensis (Isoptera, Kalotermitidae)

Abstract: Differences in the dispersal flight patterns among termite families are correlated with the difference between the two life history characteristics exhibited by this group: “separate-piece nesters” versus “single-piece nesters.” However, information remains limited on the phenology and the life history characteristics of single-piece nesters, impeding our understanding of this topic. We report the flight phenology of an Asian single-piece nester termite Neotermes koshunensis on Okinawa Island, Japan. In 1983–1984, a light-trap survey showed that N. koshunensis exhibited an extended dispersal flight period from late April to early November, peaking in June, with a female-biased sex ratio. Between 1983 and 2012, the collection of 134 whole colonies of N. koshunensis from the surrounding area confirmed the presence of alates and pre-alate nymphs within the colonies over 7 months, reflecting the extended flight season of this termite species, probably in association with the extended dispersal flight season. However, in some cases, alates and pre-alate nymphs were also retained in the colonies after the dispersal flight season (i.e., winter, from December to February). The daily number of trapped alates in 1983 was positively correlated with temperature and relative humidity; however, alate production inside the colony was also positively correlated with temperature, relative humidity, and precipitation. Thus, these environmental factors might promote the flight activity of this termite by enhancing alate production inside the colony. Furthermore, temperature also had a significantly positive effect in the model incorporating the density of alates in the colony, along with environmental factors; thus, temperature might facilitate the release of alate from colonies. The accumulation of information on the phenology and life history characteristics of alate advances our understanding of the different dispersal strategies used by termites, providing insights into how the different families have evolved.

Limits of vector calibration in the Australian desert ant, Melophorus bagoti

Abstract: Desert ants that forage solitarily continually update their position relative to the nest through path integration. This is accomplished by combining information from their celestial compass and pedometer. The path integration system can adapt when memories of previous inbound routes do not coincide with the outbound route, through vector calibration. Here, we test the speed and limit of vector calibration in the desert ant Melophorus bagoti by creating directional conflicts between the inbound and outbound routes (45°, 90°, 135°, 180°). The homeward vector appears to calibrate rapidly after training with shifts occurring after three foraging trips, yet the limit of the vector’s plasticity appears to be a maximum of 45°. At 45° conflicts, the vector calibrates the full 45°, suggesting dominance of the previous inbound memories over the outbound cues of the current trip. Yet at larger directional conflicts, vector shifts after training diminish, with foragers in the 90° and 135° conditions showing smaller intermediate shifts between the inbound memories and the current outbound vector. When the conflict is at its maximum (180°), foragers show no calibration, suggesting the outbound vector is dominant. Panorama exposure during training appears to aid foragers orienting to the true nest, but this also appears limited to about a 45° shift and does not improve with training.