Nest site selection by fire ant queens

Summary We examined nest site selection by foundresses of the polygyne form ofSolenopsis invicta. In the laboratory, foundresses were allowed to nest in control soil vs. soil inoculated with refuse from a colony ofPheidole dentata, a natural enemy. In a second experiment foundresses chose between control andS. invicta soil. More foundresses (100%) avoided the soil of a natural enemy than the soil of a conspecific colony (79%) that may accept them into the nest. Foundresses from this polygyne ant appear to avoid other colonies in general, but avoid heterospecific colonies more.     

Behavioral interactions of the invasive Argentine ant with native ant species

Summary: The Argentine ant, Linepithema humile, has invaded many areas of the world, displacing native ants. Its behavior may contribute to its competitive success. Staged and natural encounters were observed at food resources in the field, between Argentine ants and eight ant species native to northern California. There was no relation between the frequency of aggression by any ant species and the outcome of encounters, though Argentine ants were more likely than ants of native species to behave aggressively. When an ant of one species initiated an encounter of any kind with an ant of another species, the ant that did not initiate was likely to retreat. This was true of all species studied. Most encounters between ants were initiated by Argentine ants. Thus the native species tended to retreat more frequently than Argentine ants. Interactions between Argentine ants and native species at food resources, causing ants of native species to retreat, may help Argentine ants to displace native species from invaded areas.     

Imported crazy ant displaces imported fire ant, reduces and homogenizes grassland ant and arthropod assemblages

A recently introduced, ecologically dominant, exotic ant species, Nylanderia fulva, is invading the Southeastern United States and Texas. We evaluate how this invader impacts diversity and abundance of co-occurring ants and other arthropods in two grasslands. N. fulva rapidly attains densities up to 2 orders of magnitude greater than the combined abundance of all other ants. Overall ant biomass increases in invaded habitat, indicating that N. fulva exploits resources not fully utilized by the local ant assemblage. At high density, as N. fulva spreads, it eliminates the current ecologically dominant invasive ant, red imported fire ants (Solenopsis invicta). Compared to imported fire ant dominated habitat, N. fulva invasion zones have lower non-ant arthropod species richness and abundance with impacts differing by trophic category. Further, N. fulva reduces abundance and species richness of the remainder of the ant assemblage and does so in a non-random manner: impacting species with small sized workers much less than species with larger workers. In these and other ant assemblages with a large exotic component, the exotics tend to be small bodied species. As a result, N. fulva almost completely eliminates regionally distributed species, but leaves globally distributed species largely unaffected, thereby systematically favoring introduced over native diversity. S. invicta impacts wildlife and arthropod assemblage structure and is nearly ubiquitous in non-forested habitats of the Southeastern United States and Texas. Its displacement by N. fulva has critical implications for the natural systems of this region.     

The spread of the Argentine ant: environmental determinants and impacts on native ant communities

The increasing numbers of invasive species have stimulated the study of the underlying causes promoting the establishment and spread of exotic species. We tracked the spread of the highly invasive Argentine ant (Linepithema humile) along an environmental and habitat gradient on the northeastern Iberian Peninsula to determine the role of climatic, habitat and biotic variables on the rate of spread, and examine impact on native ant communities. We found the species well-established within natural environments. The mean annual rate of spread of the invasion (7.94 ± 2.99 m/year) was relatively low compared to other studies, suggesting that resistance posed by native ants in natural environments with no or low human disturbance might delay (although not prevent) the spread of the invasion irrespectively of the land-use type. Factors related to the distance to urban areas and characteristics of native and introduced populations explained the rate of spread of the invasion, while habitat-related variables determined the distribution of native ants and the impact of the Argentine ant on them. Native ant communities became more homogeneous following the invasion due to the decline of species richness and abundance. Only few species (Plagiolepis pygmaea and Temnothorax spp.) were able to cope with the spread of the invasion, and were possibly favored by the local extinction of other ant species. Taken together, our results indicate that land uses per se do not directly affect the spread of L. humile, but influence its invasive success by molding the configuration of native ant communities and the abiotic suitability of the site.     

Worker demography in the ant Formica neorufibarbis

Abstract. 1. Patterns of worker demography in the ant Formica neorufibarbis were documented under natural conditions.
2. Some workers lived at least 4 years.
3. In 4 of 5 years, colonies were more likely to retain older workers than new workers.
4. Workers persisted for more years in colonies lacking queens than in queenright colonies.     

Inbreeding-related trade-offs in stress resistance in the ant Formica exsecta

Inbred individuals and populations are predicted to suffer from inbreeding depression, especially in times of stress. Under natural conditions, organisms are exposed to more than one stressor at any one time, highlighting the importance of stress resistance traits. We studied how inbreeding- and immunity-related traits are correlated under different dietary conditions in the ant Formica exsecta. Its natural diet varies in the amount and nature of plant secondary compounds and the level of free radicals, all of which require detoxification to maintain organismal homeostasis. We found that inbreeding decreased general antibacterial activity under dietary stress, suggesting inbreeding-related physiological trade-offs.     

Impact of the invasive ant Wasmannia auropunctata (Formicidae: Myrmicinae) on local ant diversity in southern Cameroon

The little fire ant, Wasmannia auropunctata Roger, is one of the world's most destructive invasive ants. It has been present in Cameroon for more than four decades, but its impact on local ant diversity is not known. We studied impact of W. auropunctata in three disturbed habitats located in rural and urban areas. We monitored ant diversity in both invaded and noninvaded zones in each area using a combination of three sampling methods: bait, pitfall traps and visual catch in quadrat. We collected 28 species in urban area and 64 in rural area. In invaded zone, W. auropunctata made up 97.72% and 99.96% of all ant fauna and ant species richness decreased to 7 and 2 in urban and rural area, respectively. In accordance with others findings in introduced environments, the presence of W. auropunctata has severely reduced abundance and richness of local ant species in both urban and rural environments in Cameroon. Measures should therefore be put in place to prevent its introduction in natural environment as forest reserves and natural parks.     

Response of ant communities and ant–seed interactions to bush regeneration

Summary Bush regeneration programmes aim to restore native plant communities by interventions designed to assist natural recovery, supplemented by planting or direct seeding where necessary. The present study compared ground-dwelling ant communities and rates of seed removal by ants in weed-infested, regenerating and undamaged urban bushland in northern Sydney. Three replicate dry sclerophyll sites on sandstone were studied, each containing zones of weed-infested, regenerating and undamaged bushland. Canopy cover, midstorey cover, ground cover and litter depth were measured at each site. Each zone type showed distinctive vegetation and cover characteristics, particularly at the ground level. Ground foraging ants were sampled with pitfall traps, sorted to morphospecies and placed in functional groups. There were no significant differences in ant abundance, number of genera or number of morphospecies between site types. Ant diversity and equitability was highest in the undamaged zones, followed by regenerating zones, then weedy zones. There was a significant difference between zone types in the proportion of ant species in different functional groups. Weedy zones were dominated by Opportunist species whereas regenerating zones had a high proportion of Dominant Dolichoderinae. At undamaged zones, the distribution of ants across functional groups was more even. Differences in the ant communities between the three zone types were reflected by differences in interactions between ants and seeds. Seed removal rates of both native and exotic seeds were significantly lower at weedy zones than at undamaged zones, with the regenerating zones having intermediate rates. Sites subject to regeneration 4–10 years previously were intermediate between undamaged and weedy zones for ground cover, litter depth, ant species diversity and equitability, proportion of Opportunist ant species, and seed removal rates. Thus, the regeneration techniques used have been at least partially successful in restoring some aspects of the invertebrate fauna and ecological interactions typical of undamaged dry sclerophyll bushland.     

Fire effect on ground-foraging ant assemblages in northeastern Argentina

Fire is an important component of many natural ecosystems affecting plant communities and arthropods by mortality during combustion and/or indirectly through the modification of the habitat. The Iberá Natural Reserve (INR) is one of the most diverse ecosystems in northern Argentina; it is dominated by grasslands commonly affected by disturbances, such as grazing and fire. The objective of this work was to study the response of ground-foraging ant assemblages, particular species, and functional groups to an extended fire of high intensity in four natural INR habitats with >5 years of cattle exclusion (strict conservation area). A total of 12,798 ant workers of 67 species were captured in 39 sampling stations. The ant fauna was less abundant in burned sites only a few days after the fire; 6 months later, no effect was detected. Richness and abundance of ants differed among unburned habitats. However, fire effect on species richness and composition remained unclear. The rapid recovery of the ant fauna made these insects poor indicators of long-term fire-promoted changes on biodiversity in open habitats dominated by grassland, though some ant species showed a high level of habitat fidelity mainly in unburned habitats. These results agree with those from other areas of the world, indicating that ants are particularly unreliable biodiversity indicators, with the exception of severe disturbance with long-term habitat restoration. Management decisions at the INR should be oriented to preserve the closed savanna, one of the most diverse and threatened habitat of Argentina.     

Combat between large derived societies: A subterranean army ant established as a predator of mature leaf-cutting ant colonies

Summary. Mature colonies of Atta leaf-cutting ants are dominant herbivores throughout the Neotropics. Although young colonies have natural enemies, mature colonies, which live in extensive nests containing millions of workers, currently have no recognised predators. New World army ants (Ecitoninae) are specialist social predators of other ants, and the army ant Nomamyrmex esenbeckii, a primarily subterranean species, is known to prey upon young Atta colonies. Here we present the results of the first long-term study of the predator-prey interaction between N. esenbeckii and Atta. Our study establishes the army ant N. esenbeckii as the only known predator capable of successfully attacking and killing mature as well as young colonies of Atta leaf-cutting ants. In natural raids, and experimental tests, Atta rapidly recruited their largest workers (majors) as a specific defensive response to N. esenbeckii raiders and both taxa used their largest individuals in the frontline of battles. The deployment and behaviour of these large workers demonstrates a size-related division of labour and agrees with the predictions of Lanchesters Linear Law of Combat. Both taxa also used cooperative combat teams to overwhelm large combatants from the other side. The success of N. esenbeckii raids varied greatly, such that they were prevented from entering Atta nests in the least successful raids, and completely overran Atta colonies in the most successful raids. The speed and magnitude of the defensive response of mature Atta colonies was key in determining the level of success of N. esenbeckii raids.Received 12 December 2003; revised 25 March 2004; accepted 1 April 2004.Work conducted at the Smithsonian Tropical Research Institute, Apartado 2072, Balboa, Ancon, Republic of Panama     

New fungal pathogens of the red ant, Myrmica rubra, from the UK and implications for ant invasions in the USA

The red ant, Myrmica rubra, is an increasingly invasive pest species in north-eastern USA, where it is known as the European fire ant. During surveys for natural enemies in part of its native range in the UK, three previously unreported fungal pathogens developed on ants when incubated in the laboratory. These are described and illustrated: Paraisaria myrmicarum sp. nov., Hirsutella stilbelliformis var. myrmicarum var. nov., and Hirsutella subramanianii var. myrmicarum var. nov. Based on analyses of the protein coding region EF-1α and LSU?rDNA, all three described taxa are shown to be affiliated with the hypocrealean family?Ophiocordycipitaceae. The implications for the management of M. rubra in its exotic North American range using classical biological control are discussed.     

西北荒漠草原针毛收获蚁的筑巢行为

针毛收获蚁Messoraciculatus(F .Smith)是我国北方特别是西北荒漠草原的优势种蚂蚁 ,亦是重要的种子收获性蚁类 ,收获、贮藏和取食 1 0余种荒漠植物种子。自然巢穴深 80cm～ 1 3 7cm ,单一巢口 ,沿主隧道不同深度有水平延伸的各层巢室 ,巢室向四周的延伸范围随巢深减小 ,层间距拉大。自然巢穴的空间结构与社群越冬与种子的深层贮藏有着密切的关系。饲养社群筑巢行为由蚁后主导 ,起始营巢位点数与蚁后头数有关 ,每一蚁后带领 5 0～ 70头工蚁 ,营巢时程 0 5～ 0 67d 60工蚁 蚁后 ,蚁巢有多个巢口。自然与饲养社群的巢穴结构差异很大 ,但两者单一蚁后与工蚁所占的有效巢穴空间是基本一致的 ,自然社群 1 81 3 7cm3 蚁后 ,2 99cm3 工蚁 ,饲养社群 1 5 6 2 6cm3 蚁后 ,2 60cm3 工蚁     

Deleterious Wolbachia in the ant Formica truncorum

Wolbachia is a maternally inherited bacterium that may manipulate the reproduction of its arthropod hosts. In insects, it is known to lead to inviable matings, cause asexual reproduction or kill male offspring, all to its own benefit, but to the detriment of its host. In social Hymenoptera, Wolbachia occurs widely, but little is known about its fitness effects. We report on a Wolbachia infection in the wood ant Formica truncorum, and evaluate whether it influences reproductive patterns. All 33 colonies of the study population were infected, suggesting that Wolbachia infection is at, or close to, fixation. Interestingly, in colonies with fewer infected workers, significantly more sexuals are produced, indicating that Wolbachia has deleterious effects in this species. In addition, adult workers are shown to have significantly lower infection rates (45%) than worker pupae (87%) or virgin queens (94%), suggesting that workers lose their infection over life. Clearance of Wolbachia infection has, to our knowledge, never been shown in any other natural system, but we argue that it may, in this case, represent an adaptive strategy to reduce colony load. The cause of fixation requires further study, but our data strongly suggest that Wolbachia has no influence on the sex ratio in this species.     

Cuticular profiles and mating preference in a slave-making ant

The remarkable ability of slave-making ants to integrate chemically in the colonies of their host species makes them useful model systems for investigating the role of cuticular hydrocarbons in chemical recognition. The purpose of our study was to examine the influence of the rearing host species on the cuticular hydrocarbon profile and on the mating behaviour of sexuals of the slave-making ant Chalepoxenus muellerianus. Sexuals from a population parasitizing exclusively the host species Temnothorax unifasciatus were reared in the laboratory either with their natural host or another potential host species, Temnothorax recedens. C. muellerianus males reared with T. unifasciatus investigated and mounted female sexuals reared with the same host significantly more often than female sexuals reared with T. recedens. Similarly, C. muellerianus males reared with T. unifasciatus discriminated against female sexuals from natural T. recedens colonies. Males experimentally or naturally reared with T. recedens did not clearly discriminate between female sexuals reared by the two host species and only rarely engaged in mating attempts with either type of female sexuals. Chemical analyses showed that host species affect the chemical profile of C. muellerianus sexuals and vice versa. Our findings indicate that cuticular hydrocarbons might be important in the mating success of this ant species. Received 21 June 2006; revised 20 February 2007; accepted 1 March 2007.     

Extreme life history plasticity and the evolution of invasive characteristics in a native ant

Disturbance resulting from urbanization is a leading cause of biotic homogenization worldwide. Native species are replaced with widespread non-native species and ants are among the world’s most notorious invaders. To date, all documented cases of ant invasions involve exotic introduced species that are spread around the world by human-mediated dispersal. I investigated the effect of urbanization on the evolution of invasive characteristics in a native ant species, the odorous house ant, Tapinoma sessile (Say). Colony social structure, life history traits, and the spatial pattern of nest distribution were compared by sampling T. sessile across a gradient of three distinct habitats: natural, semi-natural, and urban. Results demonstrate a remarkable transition in colony social and spatial structure and life history traits between natural and urban environments. In natural habitats, T. sessile colonies are comprised of small, monogyne (single queen), and monodomous (single nest) colonies. In urban areas, T. sessile often exhibit extreme polygyny and polydomy, form large supercolonies, and become a dominant pest. Results also suggest that urban T. sessile colonies may have a negative impact on native ant abundance and diversity. In the natural environment T. sessile coexisted with a wide array of other ant species, while very few ant species were present in the urban environment invaded by T. sessile. Habitat degradation and urbanization can lead to extreme changes in social and spatial colony structure and life history traits in a native ant species and can promote the evolution of invasive characteristics such as polygyny, polydomy, and supercolonial colony structure.     

粤北蚁狮生态学的初步研究

根据多年来对粤北蚁狮的调查和试验,研究了粤北自然界穴蚁蛉的生活史,蚁狮４种生境类型,５目数十种昆虫食物分布和坐等式的捕食方式．结果表明,在一定范围内,饲食量一定时,饲食频率增大１倍,蚁狮个体发育历期缩短２０％,３５天内幼虫结茧化蛹率提高４１．７５％．     

The importance of remnants of natural vegetation for maintaining ant diversity in Brazilian agricultural landscapes

Brazil is one of the leading producers of soybeans and other annual crops, and in several regions landowners are required by law to maintain 20 % of their lands with natural vegetation (i.e. as “legal reserves”). However, there is a growing concern that some of these reserves will be subject to increased levels of disturbance or even be lost as a result of the ongoing legislation reforms. In this sense, studies that evaluate the conservation potential of retaining natural habitats within agricultural areas are of great importance. We assessed the efficiency with which remnants of natural vegetation conserve the native ant fauna in a context of intensive agriculture. We compared the structure of ground-dwelling ant assemblages between crop fields and reserves located in different farms. Ant species richness was much higher in the reserves than in the crops, and this pattern was consistent in spite of variations in the type of crop planted in each field, and in the size (39–149 ha) and vegetation (open or closed savanna) of the reserves. From 41.4 to 76.4 % of all species recorded within each farm were exclusively found in the reserves. Differences in species composition were strong not only because the reserves had much more species, but also because the species that were present in both habitats showed contrasting patterns of abundance in each habitat. Overall, our results highlight that even small remnants of natural vegetation can have a significant potential to maintain a higher diversity of ants within an agriculturally dominated landscape.     

Experimental small-scale grassland fragmentation alters competitive interactions among ant species

Different species may respond differently to habitat fragmentation. Theory predicts that abundant generalist species should be less affected by fragmentation than specialist species. In ant communities, the most abundant species is often behaviourally dominant. Thus, habitat fragmentation could alter competitive interactions between the dominant ant species and the other species. We tested this hypothesis in a long-term grassland fragmentation experiment. Fragments of different size (20.25 and 2.25 m²) were isolated by a 5-m wide strip of frequently mown vegetation. Control plots were situated in adjacent undisturbed grassland. Ant density and species composition were assessed 3 and 6 years after initiation of the experimental fragmentation. The effect of the dominant ant species on the resource use of the other species was examined at natural sugar resources (aphids and extrafloral nectaries) and at artificial sugar baits. Lasius paralienus was the most abundant ant species (72% of nests) in the grasslands examined. Species richness and forager density in the other species decreased with increasing density of L. paralienus in fragments but not in control plots. The overall forager density of the other species was positively related to their habitat niche overlap with L. paralienus. The density of foragers of the other species at sugar resources was not affected by L. paralienus forager density. The experimental fragmentation resulted in an increase in natural sugar resources in fragments. This may have reduced the intensity of interspecific competition for sugar resources. Our study shows that the grassland fragmentation altered interactions between the dominant L. paralienus and the other ant species.Electronic Supplementary Material Supplementary material is available for this article at     

Aggressive interactions between the introduced Argentine ant, Linepithema humile and the native odorous house ant, Tapinoma sessile

The Argentine ant (Linepithema humile) is an invasive species that disrupts the balance of natural ecosystems by displacing indigenous ant species throughout its introduced range. The mechanisms by which Argentine ants effectively compete against native ant species have been previously addressed in field studies that centered on interference and exploitation competition at baits and mainly examined the colony-level performance of Argentine ants. Detailed behavioral observations explaining the basis for the strong competitive ability of L. humile are comparatively rare. To gain a better understanding of the mechanisms by which Argentine ants displace native ants we examined the aggressive interactions between the Argentine ants and the odorous house ant, Tapinoma sessile in four different aggression assays: (1) worker dyad interactions, (2) symmetrical group interactions, (3) intruder introductions into an established resident colony, and (4) a resource competition assay which focused on competition for food and nesting space. Our results demonstrate a clear disparity between worker-level and colony-level fighting ability of Argentine ants and provide behavioral evidence to explain the superior interference ability of Argentine ants in group assays. Argentine ants experienced mixed success in fighting against odorous house ants in dyad interactions, but gradually gained a numerical advantage in symmetrical group interactions by active cooperation among nestmates. Results of the resource competition assay indicate that Argentine ants recruit rapidly, numerically dominate food and nesting sites, and aggressively displace T. sessile from baits. Taken together, the results of these assays allow us to pinpoint the behavioral mechanisms responsible for the remarkable competitive ability of Argentine ants.     

Is the assembly of ant communities mediated by parasitoids?

Studies of species interactions in ant communities have been a major source of evidence for the importance of interspecific competition in natural communities. One consequence of the overwhelming evidence for competition in ant communities is that the role of such "top-down" processes as predation and parasitism has been ignored. Recent evidence, however, suggests that the composition and dynamics of ant communities are influenced by highly specialized parasitoids that mediate the outcome of competition among ant species. Here I review this evidence and develop a general framework for integrating the roles of competition and parasitism in the assembly of ant communities. I then use invasions by the red imported fire ant ( Solenopsis wagneri ) and the Argentine ant ( Linepithema humile ) to show how this new framework can be used to develop testable hypotheses regarding the ecological success (or failure) of invasive ant species.