Survival Of Ants Research Articles

Effect of entomopathogenic fungi on behavior and physiology of Solenopsis invicta (Hymenoptera, Formicidae).

In an ant colony, a large number of nestmates with a similar gene pool coexist, making them more vulnerable to pathogenic attacks. These pathogens influence the behavior and physiology of the fire ant Solenopsis invicta Buren. Here, we evaluated the impact of entomopathogenic fungi (EPF) Metarhizium anisopliae on the behavior (locomotion and foraging) and physiology (biological molecules, anti-fungal activity, and survival) of S. invicta. Distance traveled and velocity significantly decreased, while turn angle and angular velocity significantly increased in ants exposed to a higher concentration of M. anisopliae compared to ants exposed to control after 36 h, which showed disturbed locomotion. Fungus infection significantly affected the foraging behavior of ants. Fungus-exposed ants spent significantly less time in the food zone (area with food) than in the inner zone (area without food). The activities of 4 enzymes, peroxidase, glutathione-S-transferase, hydrogen peroxide (H2O2), and carboxylesterase were significantly decreased. In contrast, catalase and anti-fungal activities were increased after fungal exposure compared to the control. The activity of acetylcholinesterase, which hydrolyses the important neurotransmitter acetylcholine, also decreased after fungal application compared to the control. Survival of ants was also significantly reduced after fungus infection compared to the control. Our findings help to understand the influence of M. anisopliae on the behavior and physiology of S. invicta, which will help in the management of S. invicta using the EPF M. anisopliae.

Chemistry and Functions of Imported Fire Ant Venom.

In the United States, imported fire ants are often referred to as red imported fire ants, Solenopsis invicta Buren, black imported fire ants, S. richteri Forel, and their hybrid (S. invicta × S. richteri). Due to their aggressive stings and toxic venom, imported fire ants pose a significant threat to public health, agriculture, and ecosystem health. However, venom plays a vital role in the survival of fire ants by serving various crucial functions in defense, foraging, and colony health maintenance. Numerous reviews and book chapters have been published on fire ant venom. Due to its medical importance and the expanding global distribution of these ants, fire ant venom research remains an active and highly productive area, leading to the discovery of new components and functions. This review summarizes the recent advances in our understanding of fire ant venom chemistry and its functions within fire ant colonies.

Preference and effect of gustatory sense on sugar-feeding of fire ants.

BackgroundThe red imported fire ant is one of the notorious species of ants all over the world. Sugar is one of the most important components of food and necessary for the survival of ants. Because more than 70% food of fire ants is honeydew produced by Homopteran insects such as aphids and scales.MethodologyIt is well known that beetles, flies, and honey bees can recognize the sugar taste through their legs and antennae, but in the case of fire ants, no records regarding gustatory sense were published. In the current study, considering the importance of sugar bait, we investigated the gustatory sense of the fire ant workers to sucrose via behavioral sequence and gustatory behavior. First, the feeding sequence (ethogram) of the fire ant workers on most preferred sugar (sucrose) solution was observed and categorized. Secondly, the gustatory behavior of treated fire ant workers (without flagellum and foreleg tarsi treated with HCL solution) was observed on the sucrose solution. In addition, using scanning electron microscopy (SEM) techniques, we identified the possible porous sensilla types on antenna flagellum and foreleg tarsi of fire ant workers.ResultsBased on the results of feeding sequence, foreleg tarsi of workers were the main body appendages in the detection of the sucrose droplet as compared to antennae flagellum and palps. Feeding time of treated workers with HCL solution was significantly decreased on sucrose solution as compared to those workers having no flagellum. While both types of treated workers have less feeding time in comparison to normal workers. Based on the results of feeding sequence analysis and feeding time, it is indicating that the foreleg tarsi of workers play a more important role in the detection of sucrose solution as compared to antennae flagellum. Based on the SEM results, sensilla chaetic, trichoid II, and basiconic I and II have a clear pore at their tip. This study provides a substantial basis for elucidating the gustatory function of antennal and tarsal sensilla on appendages of fire ant workers to sugars and further baits improvement for the management of fire ants.

Cadmium exposure disrupts the olfactory sensitivity of fire ants to semiochemicals

Ants are eusocial insects and have evolved sensitive chemosensory systems for social communication. However, the effect of heavy metal contamination on the olfactory sensitivity of ants remains largely unknown. Here, we investigated the survival and olfactory response of Solenopsis invicta under cadmium (Cd) exposure. As a result, exposure to dietary Cd at different concentrations (100, 300 and 500 mg/L) caused higher Cd accumulation and lower survival of the ants compared with the control (0 mg/L). Cd exposure induced diverse expression patterns of odor binding protein genes (SiOBPs) in S. invicta antenna. Specifically, the expression of SiOBP4, SiOBP11, SiOBP12 and SiOBP16 was increased by 1.84-, 1.14-, 0.83- and 1.76-fold, respectively, at 300 mg/L Cd, while SiOBP7 and SiOBP9 were suppressed as Cd concentration increased. Electroantennography (EAG) and behavioral bioassays were performed to further evaluate the effect of Cd contamination on the olfactory sensitivity of S. invicta workers to 2, 4, 6-trimethylpyridine (TMP) and 2-ethyl-3,6(5)-dimethylpyrazine (EDP), the two frequent functional semiochemicals for S. invicta. The results showed that under no Cd exposure, S. invicta workers exhibited strong EAG response and apparent residing repellence to TMP and EDP, but Cd exposure suppressed EAG response and deprived the behavioral repellence to TMP and EDP of the workers, suggesting that Cd exposure decreases the olfactory sensitivity of S. invicta to these two functional semiochemicals. Further fluorescence competitive binding assay revealed that SiOBP7 had strong binding affinity to TMP and EDP, suggesting that the decrease in olfactory sensitivity may be attributed to the inhibitory effect of Cd exposure on SiOBP7. Overall, our results suggest that Cd exposure may not only directly decrease the survival of ants, but also affect their olfactory recognition.

Formicine ants swallow their highly acidic poison for gut microbial selection and control.

Animals continuously encounter microorganisms that are essential for health or cause disease. They are thus challenged to control harmful microbes while allowing the acquisition of beneficial microbes. This challenge is likely especially important for social insects with respect to microbes in food, as they often store food and exchange food among colony members. Here we show that formicine ants actively swallow their antimicrobial, highly acidic poison gland secretion. The ensuing acidic environment in the stomach, the crop, can limit the establishment of pathogenic and opportunistic microbes ingested with food and improve the survival of ants when faced with pathogen contaminated food. At the same time, crop acidity selectively allows acquisition and colonization by Acetobacteraceae, known bacterial gut associates of formicine ants. This suggests that swallowing of the poison in formicine ants acts as a microbial filter and that antimicrobials have a potentially widespread but so far underappreciated dual role in host-microbe interactions.

Getting carbohydrates in ants: damage of the young cereal sprouts by ants of the genus Myrmica Latreille, 1804 (Hymenoptera: Formicidae), to obtain plant sap

SummaryCarbohydrate food is of high importance for survival of ant colonies. Ants are known to use sugary excretions (honeydew) of various insects, nectar of floral and extrafloral nectaries, and even sap of some trees. However, the ability of ants to use sap of herbaceous plants has not been mentioned. This is the first evidence that ants of the genus Myrmica can intentionally ‘cut off’ young cereal sprouts to obtain plant sap. The investigation was carried out in a laboratory in 2018 and 2019 and involved three ant species of the genus Myrmica [12 colonies of M. rubra (Linnaeus, 1758); eight colonies of M. ruginodis Nylander, 1846; and five colonies of M. scabrinodis Nylander, 1846]. First observations were made occasionally in 10 ant colonies during the study of ant–aphid interactions. After three days of carbohydrate starvation, ants were supplied with the plants of wheat infested with aphids of Schizaphis graminum (Rondani, 1852). Within the first day in addition to ordinary trophobiotic relations with aphids, the workers of all the studied colonies demonstrated unexpected behaviour: they ‘cut off’ some sprouts and collected sap of these plants. The experimental investigation in 15 ant colonies of various sizes (about 150, 300 and 500 workers) supplied with the plants infested or non-infested with aphids has shown that getting sap of herbs depends greatly on ant colony needs and available resources. The number of damaged plants was much higher both in the larger colonies of ants and in the absence of aphids. This way of getting carbohydrates allows ants to quickly obtain some extra food needed to maintain colony viability and seems to be one of the mechanisms promoting survival of ants in conditions of acute carbohydrate deficiency. At the same time, ants avoid using plant sap when there are more available alternative carbohydrate resources.

Lethal and sublethal effects of thiacloprid on non-target carpenter ant, Camponotus japonicus Mayr (Hymenoptera: Formicidae)

Abstract To control population of Monochamus beetles that transmit pine wood nematode, Bursaphelenchus xylophilus, a variety of insecticides have been applied to forest ecosystems in Korea. Non-target predatory insects can be directly or indirectly exposed to insecticides. We evaluated potential lethal and sublethal effects of thiacloprid on survival and behavior of carpenter ants, Camponotus japonicus Mayr. Field-collected ants were directly exposed to several food items such as thiacloprid-exposed Monochamus beetles, 10% sugar water with thiacloprid concentrations, and 10% sugar water at group and individual levels. In experiment for groups of individuals, dead beetle bodies generally had possible adverse effects on ants through dietary exposure, because two forager ants were dead or paralysis after they were exposed to thiacloprid-exposed Monochamus beetles. At individual level, dietary exposure to thiacloprid at concentrations of 10 and 50 mg/L was lethal to ants, causing paralysis and impaired walking. Mortality of ant workers was higher in direct or indirect exposure treatments than that in the control. Some ants exposed to thiacloprid showed abnormal behavior within a few days, especially at thiacloprid concentrations of 10 and 50 mg/L. However, some of them sometimes recovered from the abnormal behavior in a day. In consequence, application of thiacloprid in pine forests may disrupt species interaction and foraging behavior of ants, but the effect of thiacloprid through trophallaxis behavior should be further assessed using more extensive colonies composed of queen, workers, brood, and so on.

Experiences in Transplanting Wood Ants into Plantations for Integrated Pest Management

Ants can function efficiently as biocontrol agents in open field horticulture. Temperate wood ants can control forest pests, including species damaging forest regeneration plots and fruit plantations. Thus, they possess potential as biocontrol agents in open field horticulture, if they can persist in these systems. Here we present observationson activity and survival of wood ants transplanted from forests into different types of plantations. Mound fragments were transplanted into a conifer seedling plot, an organic and a conventional Christmas tree plantation, and into an organic apple plantation. Colonies survived at least one year in all types of plantations. In some cases, however, ants moved to new locations or migrated between mound fragments, leaving some inactive. Our compiled experiences suggest that this can be prevented by providing a minimum mound size, keeping a minimum spacing between mounds and incorporation of sand and scent marked wood pieces from donor colonies to imitate naturally occurring nests. We also observed that the ants preyed upon and significantly reduced the number of winter moth larvae (Operophtera brumata – a pest in apple and other fruit orchards) in two of four apple varieties. In conclusion, wood ants were tolerant to highly diferente habitat settings and will likely persist in most types of perennial horticultural systems, if managed properly. As they prey on winter moths and multiple other pest species, they are a potential new biocontrol agent for open agricultural systems.

Comparison of ant-associated beetle communities inhabiting mounds of forest-dwelling ants in forests and forest clearings

Red wood ant (Formica rufa group) nests contain a highly diverse community of invertebrates, which is largely due to their abundant resources and regulated microclimatic conditions. Clear-felling, however, causes nest mounds to lose surface layer moisture, thus disrupting their inner stability. To study the effects of clear-felling on ant-associated beetles (myrmecophile and non-myrmecophile), 41 nests of Formica aquilonia Yarrow, 1955 located on three clear-fells and adjacent mature forest stands were sampled, and the beetle communities between these habitats were compared. We investigated how habitat type, nest surface moisture content, nest volume, and isolation affect the community composition, species richness, and abundance of beetles. Beetle community composition or species richness did not markedly differ between clearings and forests, although total abundance was higher in forests. Also, total species richness and abundance and myrmecophile abundance increased with increasing moisture content. Overall, nests with similar moisture content and volume had similar species compositions. Nest volume was negatively correlated with myrmecophile species richness. Nest isolation was not related to species richness or abundance. The lower abundances in clearings could be problematic in the long term, as small populations are more likely to become extinct. To ensure the survival of ants and their associates, small-scale clearings should be preferred.

Experimental infection of the ant Polyrhachis furcata with Ophiocordyceps reveals specificity of behavioural manipulation

Recent studies revealed that fungi of the Ophiocordyceps unilateralis sensu lato complex are highly host-specific. Infected ants leave their colony, wander singly with convulsions and eventually bite firmly vegetal substrates in the low vegetation and maintain this position until death. Subsequently, a fungal stroma grows from the back of the ant's head and produces spores. We experimentally infected Polyrhachis furcata ants by injecting them with suspensions of blastospores from three closely related fungi of the O. unilateralis species complex: Ophiocordyceps polyrhachis-furcata, Ophiocordyceps camponoti-leonardi and Ophiocordyceps camponoti-saundersi, pathogens isolated from the ant species P. furcata, Colobopsis leonardi and Colobopsis saundersi. We monitored the survival and behaviour of ants for 30 d after blastospore injection and compared the results with negative controls. Our results showed that the number of dead ants on the floor did not show significant differences across treatments. However, the typical erratic wandering behaviour and death grip display were observed only when ants were infected by their specific parasite, O. polyrhachis-furcata. Experimental ants initiated death grip between 13 and 17 d after infection, and stayed locked in the position. We suggest that the inability of Ophiocordyceps fungi to manipulate the behaviour of non-host ant species might be responsible for the observed specificity.

Long-term impact of agriculture on the survival of wood ants of the Formica rufa group (Formicidae)

The impact of agriculture on wood ants of the Formica rufa group was investigated in a small-scale agricultural landscape with many woodland fragments in the east of the Netherlands. An inventory of nests was carried out in 1986, and repeated in 2014. The number of nests of F. rufa and F. polyctena had drastically decreased during the intervening 28 years, especially in small patches of woodland bordering a maize field. The species F. rufa, which mainly disperses by flight of the queen, seems to be better adapted to habitat fragmentation than F. polyctena, where dispersal is mainly by colony splitting. However, the flying strategy can only be successful in a landscape where most woodland fragments have a good quality habitat; in the study area, the habitat quality had deteriorated. This is ascribed to the development of a tall, nitrophilous vegetation, a result of considerable nitrogen deposition from the atmosphere and the spraying of manure. The regional survival of wood ants in the east of the Netherlands is at risk in the agricultural landscapes we studied. This is due to the increasing probability of colonies becoming extinct and the decreased probability of a queen colonizing habitat patches. However, the negative influence of agriculture on the edge vegetation of patches of woodland can be decreased by leaving a wide strip between the arable land and the woodland that receives no manure.

Selenium exposure results in reduced reproduction in an invasive ant species and altered competitive behavior for a native ant species

Competitive ability and numerical dominance are important factors contributing to the ability of invasive ant species to establish and expand their ranges in new habitats. However, few studies have investigated the impact of environmental contamination on competitive behavior in ants as a potential factor influencing dynamics between invasive and native ant species. Here we investigated the widespread contaminant selenium to investigate its potential influence on invasion by the exotic Argentine ant, Linepithema humile, through effects on reproduction and competitive behavior. For the fecundity experiment, treatments were provided to Argentine ant colonies via to sugar water solutions containing one of three concentrations of selenium (0, 5 and 10 μg Se mL−1) that fall within the range found in soil and plants growing in contaminated areas. Competition experiments included both the Argentine ant and the native Dorymyrmex bicolor to determine the impact of selenium exposure (0 or 15 μg Se mL−1) on exploitation- and interference-competition between ant species. The results of the fecundity experiment revealed that selenium negatively impacted queen survival and brood production of Argentine ants. Viability of the developing brood was also affected in that offspring reached adulthood only in colonies that were not given selenium, whereas those in treated colonies died in their larval stages. Selenium exposure did not alter direct competitive behaviors for either species, but selenium exposure contributed to an increased bait discovery time for D. bicolor. Our results suggest that environmental toxins may not only pose problems for native ant species, but may also serve as a potential obstacle for establishment among exotic species.

Purpureocillium lilacinum, potential agent for biological control of the leaf-cutting ant Acromyrmex lundii

Many leaf-cutter ant species are well known pests in Latin America, including species of the genera Acromyrmex and Atta. An environmentally friendly strategy to reduce the number of leafcutter ants and avoid indiscriminate use of chemical pesticides is biological control. In this work we evaluated the effectiveness of a strain of the entomopathogen Purpureocillium lilacinum, against worker ants from six Acromyrmex lundii field colonies, after immersions in pure suspensions at a concentration of 1×106conidiaml−1. Survival of ants treated with P. lilacinum was significantly lower than that recorded in controls, and median lethal time (LT50) was 6–7days. P. lilacinum was responsible for 85.6% (80.6–89.7) of the mortality in inoculated ants, in which we found that the percentage of other entomopathogens that naturally infected ants decreased also, suggesting a good competitive capability of the fungus. Horizontal transmission to non-inoculated ants was also evidenced, given that 58.5% (41.9–64.2) of them died because of P. lilacinum. Moreover, we tested pathogenicity for three concentrations of this strain (1.0×104, 106 and 108conidiaml−1) and found a significantly faster mortality of ants and greater median percentage of infection at 108conidiaml−1 of P. lilacinum. CL50 value was 2.8×105conidiaml−1. We thus propose the use of P. lilacinum as a biological control agent of leafcutter ants in crops and plantations.

Persistence of pollination mutualisms in the presence of ants.

This paper considers plant-pollinator-ant systems in which the plant-pollinator interaction is mutualistic but ants have both positive and negative effects on plants. The ants also interfere with pollinators by preventing them from accessing plants. While a Beddington-DeAngelis (BD) formula can describe the plant-pollinator interaction, the formula is extended in this paper to characterize the pollination mutualism under the ant interference. Then, a plant-pollinator-ant system with the extended BD functional response is discussed, and global dynamics of the model demonstrate the mechanisms by which pollination mutualism can persist in the presence of ants. When the ant interference is strong, it can result in extinction of pollinators. Moreover, if the ants depend on pollination mutualism for survival, the strong interference could drive pollinators into extinction, which consequently lead to extinction of the ants themselves. When the ant interference is weak, a cooperation between plant-ant and plant-pollinator mutualisms could occur, which promotes survival of both ants and pollinators, especially in the case that ants (respectively, pollinators) cannot survive in the absence of pollinators (respectively, ants). Even when the level of ant interference remains invariant, varying ants' negative effect on plants can result in survival/extinction of both ants and pollinators. Therefore, our results provide an explanation for the persistence of pollination mutualism when there exist ants.

Keep the nest clean: survival advantages of corpse removal in ants.

Sociality increases exposure to pathogens. Therefore, social insects have developed a wide range of behavioural defences, known as ‘social immunity’. However, the benefits of these behaviours in terms of colony survival have been scarcely investigated. We tested the survival advantage of prophylaxis, i.e. corpse removal, in ants. Over 50 days, we compared the survival of ants in colonies that were free to remove corpses with those that were restricted in their corpse removal. From Day 8 onwards, the survival of adult workers was significantly higher in colonies that were allowed to remove corpses normally. Overall, larvae survived better than adults, but were slightly affected by the presence of corpses in the nest. When removal was restricted, ants removed as many corpses as they could and moved the remaining corpses away from brood, typically to the nest corners. These results show the importance of nest maintenance and prophylactic behaviour in social insects.

ANALYSIS OF THE PREDATOR RELUCTANCE AND PREY REJECTION OF WEAVER ANTS WITH LUPROPS AS SINGLE PREY RESOURCE

ABSTRACT Massive seasonal invasion of the litter dwelling beetle, Luprops tristis (Fabricius, 1801) (Coleoptera: Tenebrionidae: Lupropini), into the residential buildings and their prolonged stay in a state of dormancy during the rainy season has been a serious nuisance in the rubber plantation belts of Kerala for the last three decades. The deterring defensive secretion of the beetles is the prime reason for the non-predation by any of the vertebrate or non vertebrate predators present in the breeding habitat or in the aggregation shelters. Recent efforts revealed that the weaver ants (Oecophylla smaragdina Fabricius, 1775) could be a potential bio-control agent of Luprops beetles. However, the possibility of its failure as a bio-control agent remains as repeated feeding on a prey item with repelling defensive gland secretion leading to development of predator reluctance and prey rejection. The present work ascertained the effect of repeated feeding of weaver ants on Luprops and the results indicate that repeated feeding did not lead to predator reluctance and point out the potential of weaver ants as an effective bio-control agent against Luprops. Low abundance of weaver ants in rubber plantations in contrast to their higher incidence in the scarce native trees in rubber plantation belts indicates that rubber tree is not a preferred host plant for weaver ants. Further, the possibility of regular feeding on Luprops that are readily available in rubber plantations, leads to questions about prey suitability and the effects on the rates of development, reproduction or survival of weaver ants which calls for post-evaluation studies in field conditions after the preliminary field trials.

Combined effects of overwintering temperature and habitat degradation on the survival of boreal wood ant

The survival of insects during diapause may be affected by overwintering temperature and other environmental stress, such as anthropogenic habitat degradation. We experimentally studied the effects of overwintering temperature (+1 and +7°C) and commercial forest clear-cutting on the overwintering survival of the forest-dwelling wood ant Formica aquilonia. We found that both the higher overwintering temperature and clear-cutting lowered the overwintering survival and body fat resources of Formica aquilonia. The survival and body fat resources were highest in lower temperature treatment forest nests and lowest in higher temperature treatment clear-cut nests. The overall survival of ants increased with higher body fat resources. It is possible that both forest clear-cutting and higher winter temperature due to possible climate warming may increase the wintertime mortality of wood ants and other forest-dwelling ants.

Detrimental Effects of Highly Efficient Interference Competition: Invasive Argentine Ants Outcompete Native Ants at Toxic Baits

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. Previous studies that examined the mechanisms by which Argentine ants attain ecological dominance showed that superior interference and exploitation competition are key to the successful displacement of native ant species. The objective of this research was to test the hypothesis that effective interference competition by Argentine ants may also be detrimental to the survival of Argentine ant colonies where Argentine ants and native ants compete at toxic baits used to slow the spread of Argentine ants. To study this hypothesis, we examined the competitive interactions between Argentine ants and native odorous house ants, Tapinoma sessile, in the presence and absence of toxic baits. Results showed that Argentine ants aggressively outcompete T. sessile from toxic baits through efficient interference competition and monopolize bait resources. This has severe negative consequences for the survival of Argentine ants as colonies succumb to the toxic effects of the bait. In turn, T. sessile avoid areas occupied by Argentine ants, give up baits, and consequently suffer minimal mortality. Our results provide experimental evidence that highly efficient interference competition may have negative consequences for Argentine ants in areas where toxic baits are used and may provide a basis for designing innovative management programs for Argentine ants. Such programs would have the double benefit of selectively eliminating the invasive species while simultaneously protecting native ants from the toxic effects of baits.

Comparisons of Upper Thermal Tolerances Between the Invasive Argentine Ant (Hymenoptera: Formicidae) and Two Native Australian Ant Species

Abstract The Argentine ant, Linepithema humile (Mayr), is a significant pest species, having become established on almost every continent, particularly in areas with a Mediterranean climate. In its introduced range, the Argentine ant has been associated with reductions in the abundance and diversity of native ant and nonant invertebrate fauna, as well as the interruption of ant–plant mutualisms. The distribution of Argentine ants has been correlated with particular abiotic factors, including soil moisture, relative humidity, disturbance, and particular soil and vegetation types. This study assessed the importance of temperature on the survival of Argentine ants and two native ant species (Iridomyrmex “rufoniger” and Rhytidoponera “convexa”) in the laboratory. Workers were placed in incubators of varying temperatures (25, 32, 40, 45, 47, and 50°C), and counts of the numbers dead and alive were recorded after 1, 2, and 3 h. The results showed that all species displayed almost 100% survival at 25, 32, 40, an...

An experimental study of the relative humidity preference and survival of the Argentine ant, Linepithema humile (Hymenoptera, Formicidae): comparisons with a native Iridomyrmex species in South Australia

The Argentine ant, Linepithema humile (Mayr), is a widespread invasive ant species that commonly displaces native ants and other ground-dwelling invertebrates in its introduced range. Previous studies have documented a relationship between the spread of Argentine ants and abiotic conditions (particularly water availability) in invaded areas, suggesting that the invasion success of Argentine ants may be related to specific abiotic factors. This study describes the relative humidity preferences and survival of Argentine ants and a dominant native ant, Iridomyrmex ‘rufoniger’ sp. group, in the laboratory. In a preference experiment, Argentine ant workers showed a significantly greater propensity than Iridomyrmex to locate themselves in containers with the highest relative humidity. A series of survival trials revealed that the survival of both species was related to the relative humidities within experimental containers. The survival of Argentine ant colonies was reduced in comparison with those of Iridomyrmex sp. after 4 h, however by 24 h both species displayed similar levels of survival in all relative humidity conditions. These findings confirm a relationship between the level of available moisture and the distribution and survival of Argentine ants, and may help to account for the current distribution and invasion success of Argentine ants in Australia.