Insectes Sociaux最新文献

Arboreal ants are ecologically important in tropical forests, but there are few studies using DNA markers to examine their population and colony structure. Colonies of the arboreal turtle ant Cephalotes goniodontus create trail networks through the canopy of the tropical forest, in dense vegetation where it is difficult to determine how long a nest is used and how neighboring colonies partition space. We monitored 53 nest sites for up to six years and, using seven microsatellite markers, genotyped samples of workers collected at or near 41 nests over 1–4 years. We calculated average relatedness within samples collected at a given location, and between samples collected at the same location in successive years, and performed pedigree analysis to predict the number of queens that produced each sample of workers. Fifteen samples were highly related (r ≥ 0.6) from single colonies, of which 11 were monogynous and the remaining four had two queens; 19 were of intermediate relatedness (0.1 ≤ r < 0.6) with 1–6 queens, and 7 were groups of unrelated workers (r < 0.1) from at least 4 queens. Colonies persisted at the same nest site for 2–6 years. The smallest distance we found separating nests of different colonies was 16.2 m. It appears that different colonies may share foraging trails. Our study demonstrates the feasibility of using a cost-efficient genotyping method to provide information on colony structure and life history of ant species.

Due to agriculture and logging, Costa Rica has lost many primary forests, making reforestation an important task. To judge the progress of reforestation, it is important to follow the reassembly of organismal communities within restored habitats. The COBIGA project near La Gamba, in the Golfo Dulce region of Costa Rica, aims at reforestation of lowland sites with native tree species. Ants, as ubiquitous and highly abundant terrestrial organisms, have a substantial influence on tropical ecosystems. The multiple roles include scavenging, predation, herbivory, and mutualistic interactions. We examined ant community responses to reveal the status of community regeneration and functional integrity. We compared the composition and diversity of the ant assemblages at three different age reforestation sites (2, 8, and 10 years old) with those at an old-growth forest as a reference site. By offering canned tuna fish at ground level along replicated transects, we observed 43 ant species representing six functional groups during the 2 months of sampling. Most of the observed ant species were omnivorous, but old-growth forests harbored a substantial number of other functional groups, such as generalized predators, arboreal predators, and arboreal omnivores. In contrast, the youngest reforestation site harbored a severely impoverished ant assemblage comprising mostly generalized polygynous and polydomous ant species from lower trophic levels. The within-site heterogeneity of the ant assemblages increased from the youngest to the oldest forest. In addition, our results show the importance of monitoring the progress of forest recovery to avoid the spread of invasive species into primary habitats.

Eastern subterranean termite, Reticulitermes flavipes Kollar (Blattodea: Rhinotermitidae), colonies forage from multiple wood and soil sources in a temperate climate. Thus, access to all nutrients may not be consistent throughout the year due to seasonal temperature changes. This study examined the changes in levels of protein, lipids, carbohydrates (simple sugars and glycogen), and amino acids in workers and soldiers during four different time intervals of the year (spring, early summer, late summer, and fall) when termites would be actively foraging. Workers and soldiers did show differences in nutrient levels and in both castes, levels of all nutrients did change seasonally. Based on the results of this study, both castes increase levels of protein, carbohydrates, and lipids as winter approaches. These findings suggest that termite soldiers may act as repletes for the colony.

Honeybees use waggle dances to inform nestmates about the locations of food and nest sites. The waggle duration corresponds to the distance to a resource, while its direction with respect to the vertical axis represents the resource direction in relation to the solar azimuth. Individual waggle runs within a dance often vary in duration and direction, and follower bees use the average spatial information for foraging. Honeybees also dance prior to nest movement, wherein waggle runs have directional similarity, but vary considerably in duration. The role of these dances, called migratory dances, has been elucidated mostly using artificially generated swarms which may not accurately represent long-term changes in the colony preceding migration. We explored temporal trends in waggle dances prior to migration from undisturbed colonies of the Asian giant honeybee, Apis dorsata. In two sites in India with either a year-round or seasonal presence of colonies, we asked whether dances are a sufficient predictor of migration. One site showed increased mean and error in the duration of dances in all colonies prior to migration. All study colonies migrated and the habitat was devoid of colonies in general. The second site was different in that all colonies had similar dance durations and error over time, although only one of the colonies migrated within the study period, while the others migrated months later. Thus, though migration is preceded by longer dances with greater error, these dances do not necessarily indicate imminent migration. Importantly, our findings suggest that the migratory response likely involves an interplay of several factors (e.g., resources, colony health) that are being constantly evaluated, and colonies may either migrate or revert to a resident state. These findings are the first observations of pre-migration dances from natural, undisturbed colonies (as opposed to artificial swarms) and are of significance as A. dorsata increasingly occupies urban areas and can potentially become invasive.

During decision − making, animals consider not only the current but also the past quality of options. For example, when humans evaluate performance (e.g. sales) of employees, they do not only consider the average performance but also the trend of performance;　ascending performance is often viewed as more favorable than descending performance. In our study, we test if non-human animals have a similar bias when they are evaluating options using house-hunting by the acorn ant, Temnothorax curvispinosus, as our model system. Our data show that when nest-site quality is static over time, ant colonies tend to prefer the nest site which was better (i.e. darker) between two nest options. However, when the nest quality changes over time—one improves and the other worsens—more colonies choose the low-quality, but improving, nest than the high-quality, but worsening, nest. These results suggest that a continuous change of option quality may influence evaluation. We discuss alternative explanations for our results, possible mechanisms, and potential ecological benefits for keeping track of the nest-site quality.

Social insects live in closely related family groups but face risks of intrusion and infection by pathogenic and parasitic microbes. To cope with the microbes invading their nests and feeding sites, social insects produce various types of antimicrobial substances. Subterranean termites occupy microbe-rich decaying wood and soil at high density, expanding their nest area by exploring and feeding on wood outward from the royal chamber (room for kings and queens). Although antimicrobial agents have been identified in many termite species, few studies have investigated those used by foraging workers in decaying wood under development, which is richer in microbes than the well-sterilized royal chamber and its surroundings. Here, we report that phenylacetic acid, an antifungal aromatic compound, is secreted by foraging workers of the Japanese subterranean termite Reticulitermes speratus. The compound was detected by gas chromatography–mass spectrometry analysis of ethyl acetate extracts of shelter papers infested with the workers, and antimicrobial tests demonstrated that it inhibits the germination and/or mycelial growth of the entomopathogenic fungi (Metarhizium anisopliae and Beauveria bassiana) and the termite egg-mimicking fungus Athelia termitophila. Our study provides new insights into the antimicrobial defense mechanisms of termites, including by combining different types of antimicrobial substances secreted by different castes, and thus the survival strategy of entomopathogenic and parasitic fungi in termite nests.

The global insect decline threatens ecosystem functioning because insects provide many essential services, such as pollination or nutrient cycling. Pollution is one of the main drivers of insect decline besides land-use change, global warming, and invasive species. Airborne particulate matter, such as diesel exhaust particles, is ubiquitous in the environment. Their effects on insects are still largely unknown. We provided queens and workers of the bumble bee Bombus terrestris with pollen spiked with diesel exhaust particles at the early colony founding stage and compared the colony development to control colonies. After 10 weeks, we investigated individual and colony-level life history traits. We did not see any effects of pollen spiked with diesel exhaust particles on worker count, brood count, worker size and relative fat body weight. These results indicate no harmful effects of diesel exhaust particles on colony founding in B. terrestris in our single-stressor setup. Our novel approach adds to the understanding of the role that airborne particulate matter plays in the global insect decline and we are looking forward to seeing similar studies with other species and additional stressors, such as heat stress or food shortages.

Social insects demonstrate two fundamentally different modes of reproduction, independent colony foundation (ICF) by single fertilized queens or dependent colony foundation (DCF) by fissioning of existing colonies into two or several new colonies (swarms). In some species, both reproductive modes occur in parallel. The benefits and disadvantages of DCF vs. ICF have been widely discussed and been subject to empirical studies, but a formal theoretical treatment of the topic is still incomplete. Taking honey bees as example, we provide a resource allocation model of colony dynamics to analyze the ecological conditions under which DCF may be favored over ICF. Using mathematical and numerical methods, we show that it critically depends on the survivorship function linking swarm size to the probability of swarm establishment whether ICF or DCF results in a higher output of surviving new colonies. Because building larger swarms requires larger inter-swarm time intervals, DCF can only be a better strategy if this disadvantage is over-compensated for by a strong size-dependent swarm survivorship and survival of single queens is very low. Colony growth rate has no effect on this decision and the impact of maximum possible colony size is negligible. Further, there is a discontinuity in the optimal swarm size, so that either a swarm size of 1 (ICF) is the best strategy, or emitting swarms of considerable size (DCF). Consequently, a direct evolutionary transition from ICF to DCF appears unlikely and may have been triggered by selective pressures promoting movement of complete nests or distributing single colonies over several nests (polydomy).

Stingless bees (Apidae, Meliponini), a group of mainly tropical, highly social bees, rely predominantly on passive thermoregulatory mechanisms for maintaining a nest-microclimate suitable for brood development. Even so, temperatures in the brood region are usually above temperatures in the nests’ periphery, which cannot be explained through passive thermoregulation alone. In the present study, we investigated temperature variations in nests of Melipona scutellaris throughout the year as well as the effective contribution of brood thermogenesis to the thermal dynamics under experimental simulations. The incubation temperatures in this stingless bee species varied significantly with ambient laboratory temperature. Thus, despite a constant temperature excess in the brood area, colonies did not control incubation temperature in a strict homeostatic manner but rather showed a heterothermic behaviour. At ambient temperatures of 25–32.5 °C, brood thermogenesis increased the temperature in the combs’ close surroundings by up to 4 °C, therewith explaining part of the temperature excess in the brood area. The residual thermal increase by almost 7° at ambient temperatures of 15 °C was, presumably, attributed to active heating by the adults. The elevated metabolic activity of the pupae between 25 and 32.5 °C suggests a lower thermal range for brood development in M. scutellaris. The adaptive advantages of both colony heterothermy and reduced incubation temperatures in the threatened native habitat of this stingless bee species, the Atlantic Rainforest in north-eastern Brazil, are discussed.

Ant colonies are often considered to be highly efficient societies skilled at cooperating and sharing workload among workers. Yet, several studies have revealed low colony activity levels and a subgroup of specialized inactive individuals, raising questions about their role. This study investigates whether these inactive ants differ in their sensitivity to environmental cues compared to other worker groups. We monitored the behavior of individually tagged workers from Myrmica rubra ant colonies, categorizing them as foragers, nurses, domestics, or inactives. Approximately one-third of the workers exhibited high levels of inactivity, forming a distinct group that remains stable over several days. Subsequently, individual tests were conducted on these ants to compare their responses to intranidal or extranidal location cues, and to task-related stimuli such as larvae or prey. In individual tests, foragers displayed distinct responses compared to internal workers. They exhibited greater responsiveness to prey, but were less inclined to care for larvae, stay in colony-marked or shaded areas, or approach nestmates. Among internal workers, except for the inactive ants, responses to various stimuli did not significantly differ. Notably, inactives had a stronger attraction to colony odor and were more likely to carry larvae when compared to foragers. Our results suggest that the inactivity of some individuals is not due to a lack of sensitivity to surrounding stimuli. Furthermore, their high propensity to interact with larvae supports the hypothesis of a “reserve caste” function, where these workers become active during periods of increased colony workload.