Caste differentiation and seasonal changes in Vespa velutina (Hym.: Vespidae) colonies in its introduced range

Since its introduction in France 10 years ago, the yellow‐legged hornet, Vespa velutina, has rapidly spread to neighbouring countries (Spain, Portugal, Belgium, Italy and Germany). It showed efficient social traits facilitating its invasive success. Only scarce and incomplete natural history studies were known from its native distribution area. Studying the biology of this species in its invasive distribution range was thus a prerequisite to the implementation of efficient control methods in a near future. During a 3‐year field survey, we collected 77 nests to investigate several of the species' key colony characteristics. Our results enabled us to accurately quantify each of the castes and to better understand their synchronicity throughout the season. Our study showed that mature nests are able to produce up to 13 000 individuals and that the size of mature nests is correlated to the number of individuals produced. This correlation enables the inference of one characteristic from the other. Furthermore, each mature nest can produce up to several hundreds of potential founder queens, a crucial datum in the light of today's unregulated spring queen trapping control campaigns. In addition, nest dissections enabled to record the incidence of nest relocation for the first time in this species. Results are discussed with regards to what is known in other Vespidae species, with a focus on Vespula species that are known to be invasive in many other countries worldwide.     

Competition between the native and the introduced hornets Vespa crabro and Vespa velutina: a comparison of potentially relevant life‐history traits

1. Invasive alien species are a major threat to biodiversity. In addition to predation and parasitism, native species might suffer from competition when invasive alien species occupy a similar ecological niche. 2. This study focused on the potential interspecific interaction between two hornets: the Asian yellow‐legged hornet, Vespa velutina, a high‐concern invasive alien species recently arrived in Europe; and the native European hornet, Vespa crabro. The two species share a similar ecological niche and V. velutina is rapidly expanding across Europe, which suggests that V. crabro might suffer from competition. 3. Under laboratory‐controlled conditions, two life‐history traits that might cause the two species to compete were investigated: (i) the ability of workers to find food sources and their flexibility in exploiting them (through individual food item choice tests and exploration assays); and (ii) the worker resistance to pathogens (through immune challenge tests). 4. The results show that trophic preference of both species highly overlaps, with a marked dietary preference for honeybees compared with other insect prey and non‐prey protein items. No differences were observed in the exploratory behaviour of both species. Finally, constitutive antibacterial activity was greater in workers of the native species than in workers of the invasive hornet. 5. This laboratory study provides a first assessment under controlled conditions of the factors affecting competition between workers of two hornet species and proposes a framework to assess, in wild contexts, the magnitude of the competition and the impact of the introduced V. velutina on the native V. crabro.     

Behavioral syndrome in a native and an invasive hymenoptera species

Recent studies have focused on the role of behavior in biological invasions. Individuals may differ consistently in time for several behavioral traits (personality) which covary (behavioral syndrome) resulting in different behavioral types, some of them favoring invasion. Social hymenopterans have a strong potential to be invaders and their success depends primarily on the foundresses’ ability to found viable colonies. They are expected to be active, explorative and bold for optimally establishing their nest. In Europe, 2 hornet species coexist: the native Vespa crabro and the invasive Vespa velutina. These 2 species may compete for nesting sites and we suggest that the initial success of V. velutina has been favored by its behavior in outperforming V. crabro for the traits involved in nest initiation. Here, we (i) defined the personality of V. crabro and V. velutina, (ii) tested for the existence of behavioral syndrome in these species, and (iii) compared their performances using an open‐field test. Our results show that V. crabro foundresses behave consistently but not V. velutina; this lack of consistency being mainly due to reduced variance among individuals. This result questions the possibility of detecting consistent behavioral differences in species having recently undergone a strong bottleneck. Both species exhibit the same correlations between activity, boldness and exploration and V. velutina clearly outperforms V. crabro for all traits. Our results suggest that activity, boldness, and exploration are implicated in both hornet nest initiation and invasion process which contributed to explain why social hymenopterans are so successful at colonization.     

Variation in the quality of Vespula vulgaris (L.) queens (Hymenoptera: Vespidae) and its significance in wasp population dynamics

Abstract

Density‐related variation in queen quality has been proposed as a possible mechanism regulating population fluctuations in Vespula species. We investigated annual variation in the quality (size, weight, and fat content) of adult V. vulgaris queens representing four stages of their life cycle (spring, founding, developing, and emerged) taken from six sites in beech forest, South Island, New Zealand. For each queen the dry weight, head width, and thorax length was measured. For a subsample of queens, the fat content was determined by ether extraction. The size of queen cells was measured from a subsample of nests. Size, weight, and fat content of queens varied between wasp colonies and sites. The smallest juvenile queens were under‐represented in the reproductive population. There was no direct link between body size and food supply. Size and weight of developing queens increased as the number of cells in the nest increased. The size of the queen cells varied significantly among layers in a nest and among nests. The under‐representation of small queens in the reproductive population suggests that queen quality may affect survival and/or competitive ability by increasing winter fat storage, nest building activity, and/or success in usurpation disputes.     

Invasion dynamics of Asian hornet, <Emphasis Type="Italic">Vespa velutina</Emphasis> (Hymenoptera: Vespidae): a case study of a commune in south-west France

Asian hornet, Vespa velutina Lepeletier nests were discovered in 2007 in Andernos-les-Bains on the south-west coast of France, 3 years after the first reported sightings in France. The number of nests increased in the commune over the following 7 years, despite local authorities enacting a destruction policy. The nests existed in close proximity to one another leading to a high density of over 10 nests per square kilometre in urban areas. New information on the chosen habitat for nests is presented, and the differences between primary and secondary locations are evident, with primary nests mostly occupying buildings and man-made structures, while secondary nests were found on trees. Using Bayesian inference methods, we fit a basic model to the observational data, which allows us to estimate key demographic parameters. This model fit is highly informative for predicting V. velutina spread and colonisation of other at-risk regions, and suggests that local control has a limited impact on the spread of V. velutina once established within a region.     

Are the spatio‐temporal dynamics of soil‐feeding termite colonies shaped by intra‐specific competition?

1. Soil‐feeding termites are abundant and diversified in neotropical forests, where they are among the major decomposers of the soil macrofauna. While niche specialisation along the humification gradient may reduce inter‐specific competition, some species are represented by numerous colonies likely to be involved in intra‐specific competition, but the subterranean nesting habits of most species of soil‐feeding termites make direct observations difficult. 2. The soldierless species Anoplotermes banksi Emerson was studied, which, unlike other Anoplotermes‐group species, builds arboreal nests that can be easily detected. To infer the biological processes driving the spatial distribution of this species, we conducted a 3‐year survey of the dynamics of colonisation of a 1‐ha plot by A. banksi. Ripley's L‐function, detecting aggregation or dispersion at various spatial scales, was used to investigate the distribution pattern of A. banksi nests, as well as the distribution of new and established nests. 3. Only one‐fourth of the nests recorded the first year were still alive after 3 years, highlighting a rapid turnover of the A. banksi nest population. Age classes were differentially affected by mortality, which was higher in young nests than in large, established nests. 4. Established nests were overdispersed at a short range, whereas young nests had a random or clumped distribution. Young nests tended to be overdispersed from established ones and were more abundant in areas with recently dead nests. Dead nests predominantly occurred where A. banksi nests were particularly abundant. Altogether, the present results indicate a negative interaction between neighbouring colonies suggesting intra‐specific competition.     

Adaptive latitudinal variation in Common Blackbird Turdus merula nest characteristics

Nest construction is taxonomically widespread, yet our understanding of adaptive intraspecific variation in nest design remains poor. Nest characteristics are expected to vary adaptively in response to predictable variation in spring temperatures over large spatial scales, yet such variation in nest design remains largely overlooked, particularly amongst open‐cup‐nesting birds. Here, we systematically examined the effects of latitudinal variation in spring temperatures and precipitation on the morphology, volume, composition, and insulatory properties of open‐cup‐nesting Common Blackbirds’ Turdus merula nests to test the hypothesis that birds living in cooler environments at more northerly latitudes would build better insulated nests than conspecifics living in warmer environments at more southerly latitudes. As spring temperatures increased with decreasing latitude, the external diameter of nests decreased. However, as nest wall thickness also decreased, there was no variation in the diameter of the internal nest cups. Only the mass of dry grasses within nests decreased with warmer temperatures at lower latitudes. The insulatory properties of nests declined with warmer temperatures at lower latitudes and nests containing greater amounts of dry grasses had higher insulatory properties. The insulatory properties of nests decreased with warmer temperatures at lower latitudes, via changes in morphology (wall thickness) and composition (dry grasses). Meanwhile, spring precipitation did not vary with latitude, and none of the nest characteristics varied with spring precipitation. This suggests that Common Blackbirds nesting at higher latitudes were building nests with thicker walls in order to counteract the cooler temperatures. We have provided evidence that the nest construction behavior of open‐cup‐nesting birds systematically varies in response to large‐scale spatial variation in spring temperatures.     

Polygyny in thief ants responds to competition and nest limitation but not food resources

Colonies of ants often house multiple queens, and variation in polygyny often tracks environmental conditions. Three hypotheses have been proposed to describe how environmental variation may account for the degree of polygyny: competition, food limitation and nest limitation. Here I evaluate these hypotheses with studies on litter-nesting thief ants (Solenopsis spp.) throughout a lowland tropical rain forest in Costa Rica. In one component, I measured how polygyny varied across a broad environmental gradient demonstrating substantial variation in resources and competition. In a second component, I manipulated the abundance of food, the spatial presentation of food and the availability of nesting space to assess the effects on queen number. The degree of polygyny increased with nest limitation and competition, but there was no indication that colonies produce queens to capitalize on food availability. The increase in queen number in response to the density of competitors suggests that an increase in queen number enhances exploitative abilities.     

Intraspecific application of the mid-domain effect model: spatial and temporal nest distributions of green turtles, Chelonia mydas, at Tortuguero, Costa Rica

The mid‐domain effect (MDE) model was developed to evaluate patterns of species richness. We applied the MDE model to intraspecific distribution patterns – the spatial and temporal nest distributions of green turtles, Chelonia mydas, at Tortuguero, Costa Rica, from 1972 to 2000. Spatial and temporal distributions of green turtle nests at Tortuguero did not exhibit significant annual variation over this time period. The spatial and temporal distribution of nests largely conformed to the predictions of the MDE model, although the spatial model has a better fit. Environmental factors that may cause deviations from the MDE model are discussed. The model also indirectly provided a first estimate of the mean spatial nesting range of individual green turtles at Tortuguero: 10.1 km (SD 8.7 km). The MDE model provides insight into intraspecific as well as interspecific distribution patterns.     

Relationship between the age of Vespa velutina workers and their defensive behaviour established from colonies maintained in the laboratory

As the structural bases of insect societies are essential to colony survival, nests must be protected from predation. Nest defence behaviours are among the most important roles assigned to worker members. However, in hornet societies, temporal polyethism (age-dependent division of labour among workers) is assumed to be weak. Few studies have investigated this phenomenon, probably because hornet nests are aggressively defended and dangerous to approach. In the present study, we propose a method for rearing nests of Vespa velutina, a species newly introduced into Europe. This method enables the handling of hornets, and thus the design of experiments. By marking all newly emerged hornets, we recorded aggressiveness in workers of different ages from three captive colonies. We observed that nest defence behaviour in V. velutina depends on the age of the workers. Nest defence appears to be mediated by the queen, probably through pheromones that promote nest organization. We also identified a previously unreported but important behaviour in V. velutina that workers are aggressive towards male hornets. This behaviour might be a strategy to avoid inbreeding. Collectively, our results provide new research perspectives for the management of social hymenopteran predators.     

Nest‐site characteristics,breeding success and competitive interactions between two recently sympatric apex predators

An influential period in avian life‐cycles is the annual breeding season, when competition over suitable nesting sites and territories is a key factor that can determine fitness and distribution, especially for species that are highly selective in their nesting habitats. We analysed nest‐site characteristics, breeding success and competitive interactions between two apex predator populations. Whereas the Short‐toed Eagle Circaetus gallicus has nested in the Judean Foothills (Israel) for a long time, the Long‐legged Buzzard Buteo rufinus has only invaded the nesting habitat of the Short‐toed Eagle during their breeding season in the last two decades. These two recently sympatric species have similar nesting ecology and frequently use the same nests. They are therefore expected to compete over nesting sites and territories. We analysed interspecific interactions between these two species by combining information from comprehensive observational, experimental, GIS analysis and remote sensing data, deriving 65 variables to characterize the nest‐sites used and the breeding success in 381 breeding attempts over four consecutive breeding seasons. To assess interspecific and intraspecific territorial behaviour and aggressiveness, stuffed Long‐legged Buzzards and Short‐toed Eagles were presented close to nests. Nest‐site characteristics overlapped substantially between species, and Long‐legged Buzzards occupied 21% of all Short‐toed Eagle nests. Intraspecific aggression rates among Long‐legged Buzzards were higher than their interspecific aggression rates with Short‐toed Eagles and also higher than intraspecific aggression among Short‐toed Eagles. Long‐legged Buzzard and Short‐toed Eagle breeding densities (1.59 ± 0.11 and 2.96 ± 0.11 pairs per 10 km², respectively) are likely to be the highest across their respective breeding distributions, with a maximum productivity of 0.96 ± 0.01 and 0.56 ± 0.05 (young fledged/breeding pair) for Long‐legged Buzzard and Short‐toed Eagle, respectively. Intraspecific interactions among both species play an important role in determining their breeding success and the spatial distribution of nesting sites. Our results suggest that interspecific competition over nesting sites and territories between both species, and the potential dominance of Long‐legged Buzzard, has both direct and indirect impacts on the spatial and demographic distribution of Short‐toed Eagles due to the recent establishment of Long‐legged Buzzard territories in the Judean breeding area.     

The dilemma of where to nest: influence of spring snow cover,food proximity and predator abundance on reproductive success of an arctic-breeding migratory herbivore is dependent on nesting habitat choice

Pink-footed geese Anser brachyrhynchus nest in two contrasting but commonly found habitats: steep cliffs and open tundra slopes. In Svalbard, we compared nest densities and nesting success in these two environments over ten breeding seasons to assess the impact of spring snow cover, food availability to nesting adults and arctic fox Vulpes lagopus (main terrestrial predator) abundance. In years with extensive spring snow cover, fewer geese at both colonies attempted to breed, possibly because snow cover limited pre-nesting feeding opportunities, leaving adults in poor breeding condition. Nesting success at the steep cliff colony was lower with extensive spring snow cover; such conditions force birds to commit to repeated and prolonged recess periods at far distant feeding areas, leaving nests open to predation. By contrast, nesting success at the open tundra slope was not affected by spring snow cover; even if birds were apparently in poor condition they could feed immediately adjacent to their nests and defend them from predators. Foxes were the main nest predator in the open tundra slopes but avian predators likely had a larger impact at the steep cliffs colony. Thus, the relative inaccessibility of the cliffs habitat may bring protection from foxes but also deprives geese from readily accessing feeding areas, with the best prospects for successful nesting in low spring snow cover years. Our findings indicate that spring snow cover, predator abundance and food proximity did not uniformly influence nesting success of this herbivore, and their effects were dependent on nesting habitat choice.     

Microgeographic genetic structure and intraspecific parasitism in the ant Leptothorax nylanderi

1. Genetic colony structure of the small central European ant Leptothorax nylanderi is affected strongly by ecological constraints such as nest site availability and intraspecific social parasitism. 2. Although L. nylanderi is generally monogynous and monandrous, more than a quarter of all nests collected in a dense population near Würzburg, Germany, contained several matrilines. As shown by microsatellite analysis, the average nest‐mate relatedness in these nests was 0.20. Genetically heterogeneous nests arise from nest take‐over by alien colonies or founding queens, a result of severe competition for nest sites. 3. In summer, more than one‐third of all colonies inhabited several nest sites at a time. Polydomy appears to be rather limited, with two or three nests belonging to a single polydomous colony. 4. Queens appear to dominate male production; only a small fraction (8%) of males was definitively not progeny of the queen present but might have been worker progeny or offspring of another queen. 5. Strong evidence for heterozygote deficiency was found and a total of nine diploid males was discovered in two colonies. These findings suggest deviation from random mating through small, localised nuptial flights.     

Seasonal reversal of competitive advantage between two spider species

Summary To test for inter- and intraspecific competition between two common orb-weaving spiders, Metepeira grinnelli and Cyclosa turbinata, I conducted separate field experiments in the spring and summer. During the spring experiment, the prey-consumption rate of Metepeira was reduced at higher inter- and intraspecific densities, but Cyclosa was only affected by intraspecific density. During the summer experiment, Metepeira prey-consumption was not affected by inter- or intraspecific densities, while Cyclosa was affected by both inter- and intraspecific densities. In addition to competition for food, during the spring experiment Cyclosa was observed displacing Metepeira but not vice versa, whereas during the summer experiment Metepeira displaced Cyclosa but not vice versa. The seasonal reversal in the competitive advantage between the species was linked to their asynchronous phenologies; in the spring most Cyclosa were larger than Metepeira, whereas in the summer most Metepeira were larger than Cyclosa. I suggest that in this system, temporal variability in the competitive abilities may promote species coexistence.     

Ants on the Move: Resource Limitation of a Litter‐nesting Ant Community in Costa Rica1

The leaf litter of tropical wet forests is replete with itinerant ant nests. Nest movement may help ants evade the constraints of stress and disturbance and increase access to resources. I studied how nest relocation and environmental factors may explain the density, size, and growth of leaf litter ant nests. I decoupled the relationships among litter depth, food abundance, and nest availability in a 4‐mo manipulation of food and leaf litter in a community of litter‐nesting ants in a lowland wet forest in Costa Rica. Over 4 mo, 290 1 m² treatment and control plots were sampled without replacement. Nest densities doubled in response to food supplementation, but did not decrease in response to litter removal or stress (from litter trampling). The supplementation of food increased the utilization of less favored nesting materials. In response to food supplementation and litter trampling, arboreal ants established nests in the litter, and growth rates of the most common ants (Pheidole spp.) increased. Colony growth was independent of colony size and growth rates of the most abundant ants. In general, I conclude that litter‐nesting ant density is driven primarily by food limitation, that nest relocation behavior significantly affects access to resource and the demographic structure of this community, and that nest fission may be a method to break the growth–reproduction trade‐off.     

Brutbiotop und Territorialit?t bei Habicht (Accipiter gentilis) und Rotmilan (Milvus milvus)

Zusammenfassung In einem Gebiet auf der Schwäbischen Alb von 432 km² mit weitgehend homogener Waldverteilung brüteten 13 Habicht- und 20 Rotmilanpaare. Die Horsthöhe über dem Boden lag bei beiden Arten oberhalb der Handbuchangaben. Eine Bevorzugung von Laubwaldhabitaten durch den Rotmilan war nicht erkennbar. Die regelmäßige intraspezifische Dispersion der Horstreviere beider Arten läßt auf das Vorhandensein intraspezifischer Territorialität schließen. Eine Regelmäßigkeit in der interspezifischen Dispersion war hingegen nicht erkennbar. Negative Einflüsse des Habichts auf den Reproduktionserfolg des Rotmilans waren ebenfalls nicht nachweisbar. Konkurrenz um Horstplätze zwischen Habicht und Rotmilan spielte im untersuchten Gebiet somit eine unbedeutende Rolle. Die Wirkung solcher Konkurrenz als ein für konstante Populationen allgemeingültiger Regulationsmechanismus nachKostrzewa et al. (1985) wird in Frage gestellt. Allein im Abstand des Horstes zum Waldrand bestand im Untersuchungsgebiet eine klare Trennung der Horstplatzansprüche beider Arten.

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Nesting habitat and territoriality in Goshawk (Accipiter gentilis) and Red Kite (Milvus milvus)

Summary Intraspecific and interspecific spacing of Goshawk and Red Kite nesting places were investigated in an area of 432 km² located in southern Germany. The area is characterized by a relatively homogeneous forest distribution. Nesting habitat data were collected over a period of four years. Thirteen breeding pairs of Goshawk und twenty breeding pairs of Red Kite were censused within the study area. The mean heights of nests above ground in both species were greater than those previously described (i. e.Cramp &Simmons 1980). The current view, that Red Kites prefer deciduous forest nesting habitats and deciduous nest trees, could not be confirmed.The regular intraspecific spacing of nesting places in both species indicates intraspecific territoriality. In contrast, no regularity in interspecific spacing could be detected. There was no noticeable influence of the Goshawk on the reproduction success of the Red Kite. Thus, competition for nesting places in the investigated area among Goshawk and Red Kite plays, if any, only a minor role. A factor seperating the two species with high significance is the distance from the nesting place to the nearest forest edge.In conclusion, the present study shows that competition for nesting places as a regulation mechanism, as proposed byKostrzewa et al. (1985), is unlikely.

     

Reproductive parameters vary with social and ecological factors in the polygynous ant Formica exsecta

Due to their haplo‐diploid sex determination system and the resulting conflict over optimal sex allocation between queens and workers, social Hymenoptera have become important model species to study variation in sex allocation. While many studies indeed reported sex allocation to be affected by social factors such as colony kin structure or queen number, others, however, found that sex allocation was impacted by ecological factors such as food availability. In this paper, we present one of the rare studies that simultaneously investigated the effects of social and ecological factors on social insect nest reproductive parameters (sex and reproductive allocation, nest productivity) across several years. We found that the sex ratio was extremely male biased in a polygynous (multiple queens per nest) population of the ant Formica exsecta. Nest‐level sex allocation followed the pattern predicted by the queen‐replenishment hypothesis, which holds that gynes (new queens) should only be produced and recruited in nests with low queen number (i.e. reduced local resource competition) to ensure nest survival. Accordingly, queen number (social factor) was the main determinant on whether a nest produced gynes or males. However, ecological factors had a large impact on nest productivity and therefore on a nest's resource pool, which determines the degree of local resource competition among co‐breeding queens and at what threshold in queen number nests should switch from male to gyne production. Additionally, our genetic data revealed that gynes are recruited back to their parental nests after mating. However, our genetic data are also consistent with some adult queens dispersing on foot from nests where they were produced to nests that never produced queens. As worker production is reduced in gyne‐producing nests, queen migration might be offset by workers moving in the other direction, leading to a nest network characterized by reproductive division of labour. Altogether our study shows that both, social and ecological factors can influence long‐term nest reproductive strategies in insect societies.     

Apparent Dear-enemy Phenomenon and Environment-based Recognition Cues in the Ant Leptothorax nylanderi

Inter- and intraspecific competition was investigated in ants of the myrmicine genus leptothorax in a deciduous woodland near Würzburg, Germany. The most common species, A. (Myrafant) nylanderi, lives in rotting pine, oak, and elder sticks and may locally reach densities of 10 nests per m². In the studied sites, only a small fraction of colonies were polydomous, i.e. single colonies typically did not inhabit several nest sites. The home ranges of nylanderi colonies overlap the ranges of other conspecific colonies and colonies of other species, especially L. (s.str.) gredleri. Foragers from different colonies encountering one another in the field back off without exhibiting strong aggression, suggesting that colonies do not defend absolute foraging territories. In laboratory experiments, the frequency and severity of agonistic interactions among workers from different colonies, all living in pine sticks, increased significantly with the distance between their nests. Workers from colonies nesting in different types of wood exhibited significantly more aggression. Experiments in which we transferred colonies from pine sticks into artificial pine or oak nests corroborate the hypothesis that nesting material strongly influences colony odour in L. nylanderi. The evolutionary significance of this apparent dear-enemy phenomenon is discussed.     

Olfactory Attraction of the Hornet Vespa velutina to Honeybee Colony Odors and Pheromones

Since the beginning of the last century, the number of biological invasions has continuously increased worldwide. Due to their environmental and economical consequences, invasive species are now a major concern. Social wasps are particularly efficient invaders because of their distinctive biology and behavior. Among them, the yellow-legged hornet, Vespa velutina, is a keen hunter of domestic honeybees. Its recent introduction to Europe may induce important beekeeping, pollination, and biodiversity problems. Hornets use olfactory cues for the long-range detection of food sources, in this case the location of honeybee colonies, but the exact nature of these cues remains unknown. Here, we studied the orientation behavior of V. velutina workers towards a range of hive products and protein sources, as well as towards prominent chemical substances emitted by these food sources. In a multiple choice test performed under controlled laboratory conditions, we found that hornets are strongly attracted to the odor of some hive products, especially pollen and honey. When testing specific compounds, the honeybee aggregation pheromone, geraniol, proved highly attractive. Pheromones produced by honeybee larvae or by the queen were also of interest to hornet workers, albeit to a lesser extent. Our results indicate that V. velutina workers are selectively attracted towards olfactory cues from hives (stored food, brood, and queen), which may signal a high prey density. This study opens new perspectives for understanding hornets’ hunting behavior and paves the way for developing efficient trapping strategies against this invasive species.     

Survival of transplanted nests of the red wood ant Formica aquilonia （Hymenoptera： Formicidae）： The effects of intraspecific competition and forest clear-cutting

The fitness and survival of ant colonies depend on the resources near their nests. These resources may be limited due to poor habitat quality or by intra- and interspecific competitions, which in extreme cases may cause the ant colony to perish. We tested the effect of intraspecific competition and habitat degradation （forest clear-cutting） on colony survival by transplanting 26 nests of the red wood ant （Formica aquilonia Yarrow, 1955） in 26 different forest areas that contained 0-11 conspecific alien nests per hectare. F. aquilonia is highly dependent on canopy-dwelling aphids, thus the removal of trees should cause food limitation. During the course of the 4-year experiment, 9 of the forests were partially clear- cut. We found that while forest clear-cutting significantly decreased the colonies＇ survival, intraspecific competition did not. As a highly polygynous and polydomous species, E aquilonia seems to tolerate the presence of alien conspecific colonies to a certain extent.