Social Insects Research Articles

Life expectancy in ants explains variation in helpfulness regardless of phylogenetic relatedness

Abstract Rescue behavior aims to free a relative from danger. Ants are particularly known for such helpfulness and, perhaps not coincidentally, also show the highest level of social organization in the animal kingdom, i.e., eusociality. However, even among social species such as ants, there is a huge variation in rescue proneness and little is understood about the underlying causes of this variation. In this study, we explore the relationship between helpfulness in the form of rescue and life expectancy, focusing on 14 ant species with diverse phylogenetic backgrounds. We posit that species with longer worker life expectancies are more prone to engaging in rescue actions. To test this, we assessed worker lifespan in each species and conducted behavioral tests simulating entrapment scenarios involving a nestmate ensnared by an artificial obstacle. Observed behaviors involved contact with the nestmate, digging around it, pulling at its body parts, and biting the entrapping obstacle. Our findings reveal that species with longer worker life expectancies exhibit higher proneness to rescue endangered nestmates, irrespective of phylogenetic relatedness. Furthermore, we found no trace of a phylogenetic signal in the life expectancies or helpfulness of workers belonging to different species. The results underscore the significance of life expectancy as a key factor influencing the likelihood of rescue behavior in ants. This phenomenon warrants further investigation, given the varied physiologies, life histories, and ecologies observed among species. Nevertheless, the impact of life expectancy on behavioral patterns in social insects suggests that this parameter is likely significant across diverse taxa.

Ageing effects of social environments in 'non-social' insects.

It is increasingly clear that social environments have profound impacts on the life histories of 'non-social' animals. However, it is not yet well known how species with varying degrees of sociality respond to different social contexts and whether such effects are sex-specific. To survey the extent to which social environments specifically affect lifespan and ageing in non-social species, we performed a systematic literature review, focusing on invertebrates but excluding eusocial insects. We found 80 studies in which lifespan or ageing parameters were measured in relation to changes in same-sex or opposite-sex exposure, group size or cues thereof. Most of the studies focused on manipulations of adults, often reporting sex differences in lifespan following exposure to the opposite sex. Some studies highlighted the impacts of developmental environments or social partner age on lifespan. Several studies explored potential underlying mechanisms, emphasizing that studies on insects could provide excellent opportunities to interrogate the basis of social effects on ageing. We discuss what these studies can tell us about the social environment as a stressor, or trade-offs in resources prompted by different social contexts. We suggest fruitful avenues for further research of social effects across a wider and more diverse range of taxa.This article is part of the discussion meeting issue 'Understanding age and society using natural populations'.

EU Social Economy: Means to ending Inequality?

In recent years, the European Union has been facing increasing technological, economic, environmental and social challenges. The issues of strengthening the social economy are becoming increasingly important in an era of instability and uncertainty in the prospects of global development. The subjects of this business model can play a positive role in achieving the UN Sustainable Development Goals, increasing productivity and competitiveness of both individual enterprises and states and their associations through increased solidarity at the territorial and local levels, reducing poverty and inequality. The social economy is designed to create quality jobs, guarantee equal learning opportunities and provide the necessary social services, especially for vulnerable segments of the population, such as migrants, persons with disabilities and unskilled workers. To realise its mission, its enterprises and organisations need to collaborate with public authorities, stakeholders and users capable of finding solutions to collective problems, such as ethical financing and socially responsible banking. This collaboration can give impetus to social inclusion, economic development and territorial cohesion in depressed underdeveloped areas and regions. Today, social indicators in EU countries such as poverty, inequality, long-term and youth unemployment continue to be high, making it difficult to ensure social sustainability. This article analyses EU policies on the social economy as well as its ecosystem in the region.

Discrimination Against Non‐Nestmates Functions to Exclude Socially Parasitic Conspecifics in an Ant

ABSTRACTSocial animals utilise various communication methods to organise their societies. In social insects, nestmate discrimination plays a crucial role in regulating colony membership. Counter to this system, socially parasitic species employ diverse behavioural and chemical strategies to bypass their host's detection. In this study, we tested whether such parasitic adaptations could be detected in the incipient stage of social parasitism that is observed as intraspecific phenomena in some social insects. The Japanese parthenogenetic ant Pristomyrmex punctatus harbours a genetically distinct cheater lineage which infiltrates and exploits host colonies. We found that intrusion of this intraspecific social parasite was defended by nestmate discrimination of host colonies without any behavioural strategies specialised in social parasitism. Most of the cheaters were eliminated through aggression by host workers that are typically observed against non‐nestmates, resulting in a low intrusion success rate for the cheaters (6.7%). Our result contrasts with the expectation from interspecific social parasitism but rather resembles the intraspecific counterpart reported in Cape honeybees (Apis mellifera capensis), illustrating the role of nestmate discrimination in defence against the intrusion of intraspecific social parasites.

Wild chimpanzees remember and revisit concealed, underground army ant nest locations throughout multiple years

Chimpanzees use spatiotemporal cognition for fruit foraging by remembering tree locations and fruiting seasons. However, the spatiotemporal cognition behind exploiting other foods has rarely been studied. Here, we investigate whether chimpanzees use memory to exploit concealed, underground army ant nests. We analyse 679 chimpanzee visits to four nests recorded during five years (2018–2022) using camera traps in a savanna habitat. We explore if chimpanzees intentionally revisit nests, study how they detect ants, and assess ant availability and chimpanzee ant consumption. Nests are concealed, scarce, and intermittently reoccupied, yet chimpanzees eat ants frequently. We find that out of 34 identified chimpanzees who visit the nests, 23 revisit at least one. Chimpanzees visit nest sites significantly more often than similar sites without nests. Individuals revisit significantly sooner and inspect significantly longer nests where they have more recently encountered ants. The apes use sight, smell, taste, touch, and probing tools, to detect ants inside nests. We provide the first evidence suggesting that chimpanzees use spatial and episodic-like memory to exploit concealed social insects throughout multiple years. Our results expand our understanding of the cognitive strategies behind chimpanzee insectivory, suggesting it may have played an important role in the evolution of primate spatiotemporal cognition.

Physiological trade-offs in male social insects: Interactions among infection, immunity, fertility, size, and age in honey bee drones

Female social insects represent a dramatic exception of the evolutionarily conserved physiological trade-off between reproduction and life span, where aging is positively correlated with reproduction. However, whether this facet of life history also pertains to male social insects, remains largely unknown. Male honey bees (drones) die in the act of copulation, placing them under opposing selective pressures. At the individual level, there is inter-male competition for a single successful mating attempt, leading to selective pressure that favor an increase in male fitness. Honey bee drones are haploid individuals and lack the allelic variation in their genome compared to diploid females. We hypothesized that this genetic limitation may result in trade-offs between pathological stress and fitness traits in honey bee males. In our study, we observed differences in size and fertility measures in old and young drones along with stressors of several endemic viruses and the transcriptional immune response. We found that infection does not appear to decrease fertility in old drones, despite evidence for a shift in immune expression away from established mechanisms. Contrary to our expectations, drones additionally do not appear to exhibit a physiological trade-off between size and fertility. These findings demonstrate that drones of different size are likely of different mating quality and that higher quality drones likely favor retaining reproductive output over immune function.

Exploring immune memory traits in the social immunity of a fungus-growing ant.

The immune system is crucial for organisms to defend against pathogens. Likewise, analogous immune features evolved against similar pressures at the superorganism scale. Upregulating hygiene to the same fungus pathogen is one assumption for convergent immune mechanisms in social insects, although more evidence of immune memory features remains to be confirmed. Here, we assess immune memory traits at the colony level in the leaf-cutting ant Atta sexdens. We exposed their fungus cultivar to both homologous and heterologous challenges with the entomopathogenic fungi Metarhizium anisopliae and Beauveria bassiana, as well as the mycoantagonistic fungi Fusarium oxysporum and Trichoderma spirale. By measuring ants' behaviours, we evaluated the capacity of A. sexdens: (i) to enhance their collective hygiene, (ii) speed their hygiene in further infections, (iii) how long this capacity lasts in the colonies and (iv) the degree of specificity to increase hygienic responses. Fungus grooming behaviour was enhanced mostly against entomopathogenic fungi, with a trend of faster reactions during homologous challenges. In general, the capacity to elicit such upregulated actions lasted for up to 30 days, but no longer than 60 days. Overall, colonies exhibited a degree of immune specificity, enhancing hygiene only in response to homologous exposures but decreasing it when infected secondarily with a different fungus, indicating flexible social immunity of A. sexdens after immune challenges.

Adaptive Route Memory Sequences for Insect-Inspired Visual Route Navigation

Visual navigation is a key capability for robots and animals. Inspired by the navigational prowess of social insects, a family of insect-inspired route navigation algorithms—familiarity-based algorithms—have been developed that use stored panoramic images collected during a training route to subsequently derive directional information during route recapitulation. However, unlike the ants that inspire them, these algorithms ignore the sequence in which the training images are acquired so that all temporal information/correlation is lost. In this paper, the benefits of incorporating sequence information in familiarity-based algorithms are tested. To do this, instead of comparing a test view to all the training route images, a window of memories is used to restrict the number of comparisons that need to be made. As ants are able to visually navigate when odometric information is removed, the window position is updated via visual matching information only and not odometry. The performance of an algorithm without sequence information is compared to the performance of window methods with different fixed lengths as well as a method that adapts the window size dynamically. All algorithms were benchmarked on a simulation of an environment used for ant navigation experiments and showed that sequence information can boost performance and reduce computation. A detailed analysis of successes and failures highlights the interaction between the length of the route memory sequence and environment type and shows the benefits of an adaptive method.

Morphology of the head-associated exocrine glands in Cornitermes cumulans with the description of a novel gland for the worker caste

Morphology of the head-associated exocrine glands in Cornitermes cumulans with the description of a novel gland for the worker caste

Adapting to Uncertainty: Foraging Strategies in Dinoponera quadriceps (Formicidae: Ponerinae)

When searching for food, animals often make decisions about where to go, how long to stay in a foraging area, and whether to return to the most recently visited spot. These decisions can be enhanced by cognitive traits and adjusted based on previous experience. In social insects, such as ants, foraging efficiency has an impact at both the individual and colony levels. The present study investigated the effect of the distance to, capture success, food size, and the reward rate on decisions of where to forage in Dinoponera quadriceps, a ponerine ant that forages solitarily and makes individual foraging decisions, in laboratory studies. We also investigated the influence of learning on the workers’ performance over successive trips to search for food by measuring the patch residence time in each foraging trip. Four scenarios were created that differed in the food reward rates, the food size offered, and the distances from the colony to the food site. Our work demonstrated that as a general rule, the D. quadriceps workers return to the place where a prey item was found on the previous trip, regardless of the distance, food size, and reward rate. When the ants did not capture prey, they were more likely to change their route to search for food. Our results also indicated a learning process for the routes of exploration, as well as the food site conditions for exploration. After repeated trips, the foragers reduced the patch residence time in areas where they did not capture food and quickly changed foraging areas, increasing their foraging efficiency.

From Egg to Adult: A Developmental Table of the Ant Monomorium pharaonis.

Ants are one of the most ecologically and evolutionarily successful groups of animals and exhibit a remarkable degree of phenotypic diversity. This success is largely attributed to the fact that all ants are eusocial and live in colonies with a reproductive division of labor between morphologically distinct queen and worker castes. Yet, despite over a century of studies on caste determination and evolution in ants, we lack a complete ontogenetic series from egg to adult for any ant species. We, therefore, present a developmental table for the Pharaoh ant Monomorium pharaonis, a species whose colonies simultaneously produce reproductive queens and completely sterile workers. In total, M. pharaonis embryonic, larval, and pupal development lasts 45 days. During embryogenesis, the majority of developmental events are conserved between M. pharaonis and the fruit fly Drosophila melanogaster. We discovered, however, two types of same-stage embryos before gastrulation: (1) embryos with internalized germ cells; and (2) embryos with germ cells outside of the blastoderm at the posterior pole. Moreover, we also found two-types of embryos following germ band extension: (1) embryos with primordial germ cells that will develop into reproductive queens; and (2) embryos with no germ cells that will develop into completely sterile workers. Together, these data show that queen and worker castes are already determined and differentiated by early embryogenesis. During larval development, we confirmed that reproductive and worker larvae proceed through three larval instars. Using anatomical and developmental markers, we can further discern the development of gyne (unmated queen) larvae, male larvae, and worker larvae as early as the 1st instar. Overall, we hope that the ontogenetic series we present here will serve as a blueprint for the generation of future ant developmental tables.

Land‐use changes influence climate resilience through altered population demography in a social insect

Land‐use changes influence climate resilience through altered population demography in a social insect

Challenges in baiting to manage fungus-growing termite colonies.

Fungus-growing termites (Termitidae: Macrotermitinae) exhibit significant diversity and abundance in tropical and subtropical ecosystems. Fungus-growing termites consume a wide range of materials, including leaf litter, woody debris, agricultural crops, and wooden structures, including houses. Their presence in termite baiting stations can impede the control of other residential termite pests, such as Coptotermes spp. Current control practices for managing fungus-growing termites are both costly and time-consuming, rendering them impractical for large-scale application. In our review, we analyzed recent biological and control studies on fungus-growing termites to identify key challenges and suggest improvements in termite management strategies. We identified 5 primary factors contributing to the low efficacy of current control measures for fungus-growing termites: (i) sporadic foraging behavior, which diminishes consistent bait intake; (ii) naturally small colony sizes; (iii) the nonmolting nature of the worker caste, reducing the effectiveness of chitin synthesis inhibitors; (iv) fungal cultivation, which delays and mitigates pesticide toxicity; and (v) wide-range of feeding niche, which lessens their consumption of cellulose-based baits. These insights are critical for developing more effective termite control strategies.

Comparative Analysis of PGRP Family in Polymorphic Worker Castes of Solenopsis invicta.

Peptidoglycan recognition proteins (PGRPs) are a class of pattern recognition receptors (PRRs) that activate the innate immune system in response to microbial infection by detection of peptidoglycan, a distinct component of bacterial cell walls. Bioinformatic studies have revealed four PGRPs in the red imported fire ant Solenopsis invicta; nonetheless, the mechanism of the immune response of S. invicta induced by pathogens is still poorly understood. The peptidoglycan recognition protein full-length cDNA (designated as SiPGRP-S1/S2/S3/L) from S. invicta was used in this investigation. According to the sequencing analysis, there was a significant degree of homology between the anticipated amino acid sequence of SiPGRPs and other members of the PGRPs superfamily. Molecular docking studies demonstrated that SiPGRPs show strong binding affinity for a variety of PGN substrates. Additionally, tissue distribution analysis indicated that SiPGRPs are primarily expressed in several tissues of naïve larvae, including fat body, hemocytes, head, and thorax, as detected by quantitative real-time PCR (RT-qPCR). Microbial challenges resulted in variable changes in mRNA levels across different tissues. Furthermore, the antibacterial effects of antimicrobial peptides (AMPs) produced by major ants infected with Metarhizium anisopliae were assessed. These AMPs demonstrated inhibitory effects against M. anisopliae, Staphylococcus aureus, and Escherichia coli, with the most pronounced effect observed against E. coli. In conclusion, SiPGRPs act as pattern recognition receptors (PRRs) that identify pathogens and initiate the expression of AMPs in S. invicta, this mechanism contributes to the development of biopesticides designed for the targeted control of invasive agricultural pests.

Termites and other social insects as emerging model organisms of ageing research: how to achieve a long lifespan and a high fecundity.

Social insects (termites, ants and some bees and wasps) are emerging model organisms of ageing research. In this Commentary, I outline which advantages they offer compared with other organisms. These include the co-occurrence of extraordinarily long-lived, highly fecund queens together with short-lived workers within colonies that share the same genetic background. I then summarize which new insights have been gained so far from social insect studies. Research on social insects has led to the development of a universal mechanistic framework underlying the regulation of ageing and other life-history trade-offs in insects: the TI-J-LiFe network (short for TOR/IIS-juvenile hormone-lifespan/fecundity). Because of its conservative nature, this network can be extended to also incorporate vertebrates. Current data for social insect models suggest that molecular re-wirings along the I-J-Fe (IIS-juvenile hormone-fecundity) axis of the network can explain the concurrent long lifespans and high fecundity of queens. During social evolution, pathways that foster a high fecundity have apparently been uncoupled from mechanisms that shorten lifespan in solitary insects. Thus, fecundity-related vitellogenesis is uncoupled from life-shortening high juvenile hormone (JH)-titres in the honeybee and from insulin/insulin-like growth factor signalling (IIS) activity in ants. In termites, similarly, vitellogenesis seems tissue-specifically unlinked from JH signalling and IIS activity might have lost life-shortening consequences. However, as in solitary animals, the downstream processes (Li of the TI-J-LiFe network) that cause actual ageing (e.g. oxidative stress, transposable element activity, telomere attrition) seem to differ between species and environments. These results show how apparently hard-wired mechanisms underlying life-history trade-offs can be overcome during evolution.

Efficacy and utility of isocycloseram a novel isoxazoline insecticide against urban pests and public health disease vectors.

Isoxazolines inhibit γ-aminobutyric acid chloride channels in insects and acarids by binding to postsynaptic receptors. This prevents chloride influx, leading to depolarization/hyperexcitation, paralysis, and death. Here, we evaluated the potential utility of a novel isoxazoline, isocycloseram, against several urban insect pests. Isocycloseram was active at low doses against the German cockroach, Blattella germanica (L.)[median lethal dose (LD50) 5-15 ng per insect at 72 h, topical assays]; Argentine ant (Linepithema humile Mayr), Pharaoh ant (Monomorium pharaonis (L.), common bed bug (Cimex lectularius (L.) (approximately 40 mg m-2, residual surface spray); Eastern subterranean termite (Reticulitermes flavipes (Kollar)and Formosan subterranean termite (Coptotermes formosanus Shiraki) (5 μg g-1 w/w, tunneling assays); and mosquito, Anopheles stephensi Liston (120 and 150 mg m-2 treated surfaces, aged indoors for 9 months). Additionally, cockroach gel bait at 1% isocycloseram (w/w) caused 95-100% mortality in German, American (Periplaneta americana (L.), and oriental (Blatta orientalis (L.) cockroaches within 5-14 days. Isocycloseram proved to be active against both laboratory and field populations of German cockroaches at doses lower or equal to those of other chemicals. Ants, bed bugs, and mosquitoes readily acquired lethal doses of isocycloseram from different surfaces treated with formulated products. Given its non-repellent nature, delayed effects, and activity at low rates, isocycloseram can be a very effective compound against subsocial, social, and other human disease vector insect pests. © 2024 Society of Chemical Industry.

Binding properties of olfactory proteins to host volatiles, free fatty acids and cuticular hydrocarbons in the termite Reticulitermes aculabialis

As eusocial insects prevalent in tropical and subtropical regions, termites are characterized by highly organized behaviors and exceptional adaptability, rooted in caste differentiation and chemical communication. These traits make them excellent models for studying insect social structures and ecological interactions. Investigating how termites use chemical signals to perceive and respond to their environment provides insights into their coordination and adaptation within complex ecosystems. This study delved into the chemosensory mechanisms of Reticulitermes aculabialis, examining the interactions of four olfactory proteins with 70 ligands, including host volatiles, cuticular hydrocarbons (CHCs), and free fatty acids (FFAs). Molecular docking simulations revealed varied affinities of the olfactory proteins for long-chain hydrocarbons (n-C23 to n-C28), suggesting a nuanced chemical communication system through specific hydrocarbon detection. RacuCSP1 and RacuCSP2 exhibited specific binding to linoleic acid and undecanoic acid, respectively, highlighting the significance of FFAs in the physiological and behavioral processes of termites. The four olfactory proteins showed a strong affinity for longifolene in fluorescence competitive binding experiments. Notably, RacuOBPs exhibited unique affinities for terpenoid volatiles such as β-lonone and neocembrene, while RacuCSPs specifically bound with terpenoids like 3-carene, myrtenol, α-pinene oxide and β-pinene indicating their critical roles in host detection. Behavioral observations following gene silencing revealed that RacuOBP5 was essential for recognizing longifolene and α-lonone recognition, while RacuCSP1 was key for detecting α-pinene in termites. These findings enhance our understanding of the termite chemosensory system and offer insights for developing precise pest management strategies.

Central place foragers, prey depletion halos, and how behavioral niche partitioning promotes consumer coexistence

Many seabirds congregate in large colonies for breeding, a time when they are central place foragers. An influential idea in seabird ecology posits that competition during breeding results in an area of reduced prey availability around colonies, a phenomenon known as Ashmole's halo, and that this limits colony size. This idea has gained empirical support, including the finding that species coexisting within a colony might be able to do so by foraging on a single prey species but at different distances. Here, we provide a comprehensive mathematical model for central place foragers exploiting a single prey in a two-dimensional environment, where the prey distribution is the result of intrinsic birth and death, movement in space, and mortality due to foraging birds (we also consider a variant tailored toward colonial social insects). Bird predation at different distances occurs according to an ideal free foraging distribution that maximizes prey delivery under flight and search costs. We fully characterize the birds' ideal free distribution and the prey distribution it generates. Our results show that prey depletion halos around breeding colonies are a robust phenomenon and that the birds' ideal free distribution is sensitive to prey movement. Furthermore, coexistence of several seabird species on a single prey easily emerges through behavioral niche partitioning whenever trait differences between species entail trade-offs between efficiently exploiting a scarce prey close to the colony and a more abundant prey far away. Such behavioral-based coexistence-inducing mechanism should generalize to other habitat and diet choice scenarios.

Neuropeptides specify and reprogram division of labor in the leafcutter ant Atta cephalotes.

Social insects offer powerful models to investigate the mechanistic foundation of elaborate individual behaviors comprising a cooperative community. Workers of the leafcutter ant genus Atta provide an extreme example of behavioral segregation among many phenotypically distinct worker types. We utilize the complex worker system of Atta cephalotes to test the molecular underpinnings of behavioral programming and, in particular, the extent of plasticity to reprogramming. We identify specific neuropeptides as mediators of worker division of labor in A. cephalotes , finding two neuropeptides associated with characteristic behaviors of leafcutting and of brood care. Manipulation via genetic knockdown or by injection of these neuropeptides led to stark loss or gain of each behavior and to transcriptomic shifts in the predicted direction, that is, towards gene pathways expressed in the natural caste. We also compare specific A. cephalotes worker transcriptomes with those of orthologous workers of the eusocial mammal, the naked mole rat H. gaber , revealing global similarities between caste-biased expression and link to specific roles of our studied neuropeptides in ants. This work underscores the essential function of neuropeptides in establishing complex social behavior and a remarkable plasticity among individual behavioral types.

Genomic architecture in social insects is more strongly associated with phylogeny than social behavior

Abstract The evolution of sociality in insects has been predicted to reduce effective population sizes, in turn leading to changes in genome architecture, including higher recombination rates, larger genomes, increased GC-biased gene conversion (gBGC), and greater intragenomic variation in GC content to maintain castes through differential methylation. As the number of sequenced insect genomes continues to grow, it remains an open question which, if any, of these genomic features are consistent across social insect genomes. A major challenge to determining such commonalities has been the lack of phylogenetically controlled analyses across independent origins of sociality. Of the 15 Hymenoptera species for which recombination rate was available, social species had higher rates of recombination. Next, we conducted a broader analysis of genome architecture by analyzing genome assemblies for 435 species of Hymenoptera and 8 species of Blattodea to test if GC content, genome size, distribution of CpG sites or codon bias repeatedly differed between social and nonsocial species. Overall, there was little support for predictable changes in genome architecture associated with sociality across Hymenoptera, after accounting for phylogenetic relationships. However, we found a significant negative relationship between sociality and GC content within the family Apidae and a significant negative relationship between sociality and genome size within the family Halictidae. In all, these results suggest that unique origins of social behavior may produce unique trends in genomic architecture. Our study highlights the need to examine genome architecture across independent origins of social behavior.