Argentine Ant Research Articles

Nutritional needs and mortality risk combine to shape foraging decisions in ants.

When foraging, internal needs for particular nutrients might affect food choice, and external constraints, such as predation risk, might impact trade-offs between foraging and risk avoidance. Examining both internal and external constraints simultaneously can provide important insights into how animals make decisions. We examined how internal nutritional needs and external cues of mortality risk jointly impact the foraging behavior of ants. Ant colonies require carbohydrates to support workers energetically and proteins to raise brood. Furthermore, colonies adjust their foraging activity in response to the environment, such as food availability and the presence of predators or heterospecifics. Here we examine the foraging decisions of groups of Argentine ants Linepithema humile, which differ in their nutritional needs in high-risk environments. We starved groups of ants for either proteins or carbohydrates and determined the foraging choices that ants made when cues of heterospecifics were present. We found that ants preferentially forage for carbohydrates in high-risk conditions. Furthermore, starvation for carbohydrates increased the ants' preference for carbohydrates, even when cues of heterospecifics were present at both carbohydrates and protein resources. Starvation for protein also resulted in preferential foraging for carbohydrates, but it increased visitation to a protein food source in high-risk environments compared to when ants were starved for carbohydrates or for both resources. Examining the effect of both nutrition and mortality risk on foraging simultaneously provides insights about state-dependent risk-taking behavior that may have important implications for predicting the invasion of species into novel habitats.

Genetic divergence and aggressiveness within a supercolony of the invasive ant Linepithema humile

Biological invasions constitute an opportunity to study the evolutionary processes behind species’ adaptations. The invasive potential of some species, like the Argentine ant (Linepithema humile), has likely been increasing because they show low intraspecific competition. However, multiple introductions over time or genetic divergence could increase the probability of intraspecific competition, constituting barriers for their dispersal and thus, decreasing invasive success. Here, we studied the genetic and behavioural variability of L. humile workers collected at six locations on the NW coast of the Iberian Peninsula, a possible scenario for multiple introductions and population divergence, due to its high level of maritime traffic and complex coastal geography. We analysed behaviours related to spatial navigation (exploration, wall-following), resources acquisition, and competition (inter and intraspecific aggressiveness) through two relevant seasons for the nest ecology: spring and autumn. Genetic analyses using microsatellites indicated that the nests studied belonged to the most spread supercolony in South Europe. However, we identified the existence of two genetically differentiated clusters in Galiza. Lethal interactions were found between workers from different and similar genetic clusters, but a trend suggests higher agonistic behaviours between the two genetic groups. Genetic differences were positively correlated with the geographical distance, but aggressiveness was not correlated with any of them. Ants from each of the tested nests expressed different behaviours with high plasticity through time. Ants from all nests showed more exploration and aggressiveness, less wall-following and faster detection of food in autumn than in spring, with no intraspecific aggressiveness observed in spring. Our findings suggest competition between nests of the same supercolony and behavioural seasonal variability, supporting the hypothesis of divergent evolutionary processes. The results of our work question the assumed unity of supercolonies of this species and offer insights for understanding the future adaptation of L. humile in the introduced areas.

Predicting the Potential Suitable Area of the Invasive Ant Linepithema humile in China under Future Climatic Scenarios Based on Optimized MaxEnt

Linepithema humile (Mayr, 1868) (Hymenoptera: Formicidae) is one of “100 of the world’s worst invasive alien species” listed by the International Union for Conservation of Nature and Natural Resources (IUCN). Although native to South America, this ant has spread worldwide via international trade. Currently, L. humile has not been found in China, and if it invades China, it might pose a potential risk to the native invertebrates, vertebrates, plants, and human livelihoods. Based on 2432 global occurrence records and ten bioclimatic variables, the optimized MaxEnt model was used to predict the potential suitable areas of L. humile in China. We analyzed the important bioclimatic variables affecting the potential suitable areas, and determined the changes in potential suitable areas under future climatic scenarios. Our results indicated that the mean temperature of the coldest quarter (Bio11), precipitation of the coldest quarter (Bio19), mean temperature of the wettest quarter (Bio8), and precipitation of the warmest quarter (Bio18) were the most important bioclimatic variables. Under the current climatic scenarios, the potential suitable area of L. humile in China is 80.31 × 104 km2, which is mainly located in Fujian, Zhejiang, Hunan, Jiangxi, Guangxi, Yunnan, and Hubei. Under future climate scenarios over coming decades, the potential suitable areas of L. humile showed an overall increase and a shift to higher latitudes, which indicated the invasion risk of L. humile in China will increase under climate change. Our findings provide the theoretical guidance for the early warning and monitoring of L. humile in China.

Alien vs. herbivore: ant-mediated plant defense as an option for biological control of leafcutter ants

Leafcutter ants are a major pest in vineyards in Argentina, but their damage to vine plants has not been sufficiently quantified. Biological control against leafcutter ants has not been successful so far. Sugary rewards can trigger ants to act as plant bodyguards against a wide range of herbivores. The Argentine ant Linepithema humile (Mayr) is a common invader of vineyards worldwide and has a strong preference for carbohydrates. In a first 10-week field experiment, we attracted L. humile ants to a group of plants using sugar feeders, while no feeders were used for a second group. Ant-excluded control plants were also deployed. We quantified the damage inflicted by the leafcutter ant Amoimyrmex bruchi (Forel) on potted vines with and without L. humile ants. In a second short field experiment, we evaluated the impact of L. humile on A. bruchi foraging through the quantification of foraging activity and the amount of transported material as a function of L. humile presence. We found that A. bruchi caused >90% leaf area reductions in plants without L. humile, while plants where the species was present were rarely attacked and leaves developed similar to those of ant-excluded controls. Active interaction with L. humile decreased A. bruchi’s foraging activity and the amount of material transported by it. This is the first report of A. bruchi as a vineyard pest and the first quantification of the damage inflicted by a leafcutter ant on organic grapevines. We demonstrate that L. humile defends vine plants against herbivore pests and artificial sugar sources boost can this defense service. The development of biological control strategies that include the ecological services of ants as natural enemies of herbivorous pests could become a useful tool in sustainable viticulture and horticulture.

First Polycipivirus and Unmapped RNA Virus Diversity in the Yellow Crazy Ant, Anoplolepis gracilipes.

The yellow crazy ant, Anoplolepis gracilipes is a widespread invasive ant that poses significant threats to local biodiversity. Yet, compared to other global invasive ant species such as the red imported fire ant (Solenopsis invicta) or the Argentine ant (Linepithema humile), little is known about the diversity of RNA viruses in the yellow crazy ant. In the current study, we generated a transcriptomic database for A. gracilipes using a high throughput sequencing approach to identify new RNA viruses and characterize their genomes. Four virus species assigned to Dicistroviridae, two to Iflaviridae, one to Polycipiviridae, and two unclassified Riboviria viruses were identified. Detailed genomic characterization was carried out on the polycipivirus and revealed that this virus comprises 11,644 nucleotides with six open reading frames. Phylogenetic analysis and pairwise amino acid identity comparison classified this virus into the genus Sopolycivirus under Polycipiviridae, which is tentatively named “Anoplolepis gracilipes virus 3 (AgrV-3)”. Evolutionary analysis showed that AgrV-3 possesses a high level of genetic diversity and elevated mutation rate, combined with the common presence of multiple viral strains within single worker individuals, suggesting AgrV-3 likely evolves following the quasispecies model. A subsequent field survey placed the viral pathogen “hotspot” of A. gracilipes in the Southeast Asian region, a pattern consistent with the region being recognized as part of the ant’s native range. Lastly, infection of multiple virus species seems prevalent across field colonies and may have been linked to the ant’s social organization.

Variation in Argentine ant (Linepithema humile) trophic position as a function of time

Variation in Argentine ant (Linepithema humile) trophic position as a function of time

Chemical identification of an active component and putative neural mechanism for repellent effect of a native ant's odor on invasive species.

The invasive Argentine ants (Linepithema humile) and the red imported fire ants (Solenopsis invicta) constitute a worldwide threat, causing severe disruption to ecological systems and harming human welfare. In view of the limited success of current pest control measures, we propose here to employ repellents as means to mitigate the effect of these species. We demonstrate that cuticular hydrocarbons (CHCs) used as nestmate-recognition pheromone in the Japanese carpenter ant (Camponotus japonicus), and particularly its (Z)-9-tricosene component, induced vigorous olfactory response and intense aversion in these invasive species. (Z)-9-Tricosene, when given to their antennae, caused indiscriminate glomerular activation of antennal lobe (AL) regions, creating neural disarray and leading to aversive behavior. Considering the putative massive central neural effect, we suggest that the appropriate use of certain CHCs of native ants can facilitate aversive withdrawal of invasive ants.

Three new exotic species of ants (Hymenoptera, Formicidae) for Madeira, with comments on its myrmecofauna

Three new exotic species of ants are recorded for the Macaronesian island of Madeira:Cardiocondyla obscuriorWheeler, 1929,Lepisiota capensis(Mayr, 1862) andPheidole navigansForel, 1901. The well-known invasivePheidole megacephalais now rare on Madeira, possibly because of competition withP. navigans. We did not come across the Argentine ant –Linepithema humile, which was once very common in the Funchal area. Despite extensive searching, the presumed endemicTemnothorax wollastoni(Donisthorpe, 1940) remains unknown other than from the type material. Presence, abundance and extinction of invasive and exotic ants are dynamic processes and we stress the importance of continuous sampling.

Seed removal decrease by invasive Argentine ants in a high Nature Value farmland

Seed dispersal by ants is an important ecological process that maintains the structure anddiversity of natural communities, however, it is vulnerable to biological invasions. Argentine ants are one of the worst invasive ant species and cause severe changes in ecosystem processes and native ant biodiversity declines in invaded sites. Here, we studied seed removal by ants combining observations and a cafeteria experiment with seeds of four myrmecochorous plant species (Centaurea sphaerocephala, Rosmarinus officinalis, Silybum marianum, and Ulex australis) in two sites (invaded and uninvaded) located in the Mediterranean Montado ecosystem and classified as High Nature Value farmland (HNV). Significant differences in daily seed removal rates were found between the two study sites. In uninvaded sites, several native ant species were attracted to the seeds, resulting in all seeds being removed rapidly. The majority of seed removal events were carried out by two key seed disperses Pheidole pallidula (71%) and Aphaenogaster iberica (26%) with a clear preference for diaspored with larger and heavier elaiosome (i.e., C. sphaerocephala, S. marianum). By contrast, while the Argentine ant showed some interest (68% of seeds were interacted with), no seed removal events were observed. The extirpation of the local ant fauna by the Argentine ant and its inability to ensure seed dispersal services may lead to the interference and eventually to the collapse of seed dispersal of the four studied myrmecochorous plants in the invaded site in the future. We argue that these discrete but severe consequences of an invasive species on a key ecological process may strongly affect the functioning of the Montado ecosystem.

The effect of resource availability on interspecific competition between a native and an invasive ant.

Interspecific competition influences the composition of ecological communities. Species may differ in their needs for different resources, therefore resource availability may determine the outcome of interspecific interactions. Species often compete over food, shelter or both. When more than one resource is limited, different species may prioritize different resources. To determine the impact of resource availability on the competitive relationship between an invasive and a native species, we examined interactions between groups of the invasive Argentine ant (Linepithema humile) and the native odorous ant (Tapinoma sessile) over (1) food, (2) shelter or (3) both simultaneously. We further examined the mechanisms underlying the competitive relationship, asking whether aggressive interactions, exploratory behaviour or the order of arrival at a resource explained resource use. Shelter was preferred by both species when no competitors were present. In a competitive setting, L. humile groups controlled shelter through aggressive displacement but lost control over food due to investment of workers in the control of shelter. Thus, there are tradeoffs when competing over multiple resources and aggressive interactions allow invasive species to displace native species from a preferred resource.This article is part of the theme issue ‘Intergroup conflict across taxa’.

The Effect of Diet on Colony Recognition and Cuticular Hydrocarbon Profiles of the Invasive Argentine Ant, Linepithema humile.

Simple SummaryThe membership of social insect colonies is defined by chemical pheromones on the bodies of colony members. In nearly all ant species that have been studied, these pheromones have been shown to be genetically based. In some cases, however, environmentally derived odors have been implicated as colony recognition cues. The widely introduced and invasive Argentine ant is well known for forming massive “supercolonies” in its introduced ranges. Previous studies have implicated both genetic and diet-derived chemicals in the colony recognition systems of introduced populations. Here, we perform feeding experiments, in both realistic field settings and the lab, and show that dietary changes do not cause behavioral changes in the field, as well as under most laboratory conditions. However, one exception was found, in which reduced aggression was recorded in one of the laboratory feeding treatments (with crickets as the dietary item), but, nevertheless, not of sufficient magnitude to explain the unusual colony structure of introduced Argentine ants. We conclude that dietary shifts during introduction to new ranges do not account for the origin of Argentine ant supercolonies.Ants are some of the most abundant and ecologically successful terrestrial organisms, and invasive ants rank among the most damaging invasive species. The Argentine ant is a particularly well-studied invader, in part, because of the extreme social structure, known as unicoloniality, that occurs in introduced populations. Unicoloniality is characterized by the formation of geographically vast supercolonies, within which territorial behavior and intraspecific aggression are absent. Although there is considerable evidence supporting a genetic basis for the odor cues involved in colony recognition, some studies have suggested that diet may also influence colony recognition cues and, thus, colony structure. Here, we test the role for insect-derived recognition cues by performing a diet supplementation experiment in a natural field setting, and a more extreme dietary manipulation experiment in the lab. After one month, in both the field and the lab, we found that aggressive supercolonies remained aggressive toward each other and non-aggressive nests (from the same supercolony) remained non-aggressive, regardless of dietary treatment. In one lab treatment, we did observe a significant decrease in the level of aggression between different supercolonies that were fed the same diet, but aggression was still frequent. We did not see any evidence for cuticular hydrocarbon odor cues being transferred from prey to ants in any of the field treatments. In the more extreme lab treatment, however, several cuticular hydrocarbons were acquired from both roach and cricket insect prey (but not Drosophila). Based on these data, we conclude that dietary changes are unlikely to underlie changes in behavior or colony structure in Argentine ants in real-world settings. However, these results indicate that caution is warranted when interpreting the behaviors of animals that have been reared on diets that are substantially different from natural populations.

Invasive predators affect community-wide pollinator visitation.

Disruption of plant-pollinator interactions by invasive predators is poorly understood but may pose a critical threat for native ecosystems. In a multiyear field experiment in Hawai'i, we suppressed abundances of globally invasive predators and then observed insect visitation to flowers of six native plant species. Three plant species are federally endangered (Haplostachys haplostachya, Silene lanceolata, Tetramolopium arenarium) and three are common throughout their range (Bidens menziesii, Dubautia linearis, Sida fallax). Insect visitors were primarily generalist pollinators, including taxa that occur worldwide such as solitary bees (e.g., Lasioglossum impavidum), social bees (e.g., Apis mellifera), and syrphid flies (e.g., Allograpta exotica). We found that suppressing invasive rats (Rattus rattus), mice (Mus musculus), ants (Linepithema humile, Tapinoma melanocephalum), and yellowjacket wasps (Vespula pensylvanica) had positive effects on pollinator visitation to plants in 16 of 19 significant predator-pollinator-plant interactions. We found only positive effects of suppressing rats and ants, and both positive and negative effects of suppressing mice and yellowjacket wasps, on the frequency of interactions between pollinators and plants. Model results predicted that predator eradication could increase the frequency of insect visitation to flowering species, in some cases by more than 90%. Previous results from the system showed that these flowering species produced significantly more seed when flowers were allowed to outcross than when flowers were bagged to exclude pollinators, indicating limited autogamy. Our findings highlight the potential benefits of suppression or eradication of invasive rodents, ants, and yellowjackets to reverse pollination disruption, particularly in locations with high numbers of at-risk plant species or already imperiled pollinator populations.

Efficacy of Selected Polyols Against Argentine Ant When Incorporated Into Alginate Hydrogel Beads, 2022

Efficacy of Selected Polyols Against Argentine Ant When Incorporated Into Alginate Hydrogel Beads, 2022

Laboratory Evaluation of Insecticide Residues on Irrigation Pipes for Control of Argentine Ant, 2022

Laboratory Evaluation of Insecticide Residues on Irrigation Pipes for Control of Argentine Ant, 2022

IN1336] Argentine ant, Linepithema humile (Mayr) (Insecta: Hymenoptera: Formicidae)

The Argentine ant, Linepithema humile (Mayr), is an insect native to South America, but an invasive species in many parts of the world. It is globally distributed. Linepithema humile is considered a pest species, primarily due to its feeding habits of tending and protecting honeydew producing insects, such as scale insects, which are often damaging to crops and ornamental plants. This aggressive, populous ant species also has a negative effect on native ant species. Linepithema humile colonies have multiple queens, allowing colonies to grow and spread rapidly. Under certain conditions, the argentine ant may also become a household pest if it finds a way into homes. Linepithema humile has been designated as a tramp ant species, meaning that it has an incredible ability to spread and establish in new areas and is difficult to control. Linepithema humile, like other tramp species, can establish in new locations quickly due to the multi-queen nature of the colonies, their abitlity to forage and find resources, and the extensive network of interrelated colonies they are able to form. This document provides an in-depth synopsis of the insect's life history, biology, and management.

Multiyear drought exacerbates long-term effects of climate on an invasive ant species.

Invasive species threaten biodiversity, ecosystem function, and human health, but the long‐term drivers of invasion dynamics remain poorly understood. We use data from a 28‐yr ongoing survey of a Northern California ant community invaded by the Argentine ant (Linepithema humile) to investigate the influence of abiotic and biotic factors on invasion dynamics. We found that the distribution of L. humile retracted following an extreme drought that occurred in the region from 2012 to 2015. The distribution of several native ant species also contracted, but overall native ant diversity was higher after the drought and for some native ant species, distributions expanded over the 28‐yr survey period. Using structural equation models, we found the strongest impact on the distribution of L. humile was from direct effects of climate, namely, cumulative precipitation and summer maximum temperatures, with only a negligible role for biotic resistance and indirect effects of climate mediated by native ants. The increasing drought and high temperature extremes projected for northern California because of anthropogenic‐driven climate change may limit the spread, and possibly the impact, of L. humile in invaded regions. The outcome will depend on the response of native ant communities to these climatic stressors.

What is that smell? Hummingbirds avoid foraging on resources with defensive insect compounds

Hummingbirds utilize visual cues to locate flowers, but little is known about the role olfaction plays in nectar foraging despite observations that hummingbirds avoid resources occupied by certain insects. We investigated the behavioral responses of both wild and captive hummingbirds to olfactory cues of hymenopteran floral visitors, including native wood ants (Formica francoeuri), invasive Argentine ants (Linepithema humile), and European honeybees (Apis mellifera). We demonstrate for the first time that hummingbirds use olfaction to make foraging decisions when presented with insect-derived chemical cues under field and aviary conditions. Both wild and captive hummingbirds avoided foraging on feeders with defensive chemicals of F. francoeuri and aggregation pheromones of L. humile, but showed no response to honeybee cuticular hydrocarbons. Our experiments demonstrate the importance of olfaction in shaping hummingbird foraging decisions.Significance statementRecent reviews reveal that avian olfaction is not just limited to vultures and a few taxa. We demonstrate that a very charismatic group, hummingbirds, avoid defensive and aggregatory chemical cues from insects present at nectar resources. Olfactory cues can provide critical information about the presence and potential threat of insect floral visitors. This study raises new questions about the underrated importance of olfaction in avian foraging and specifically, hummingbird foraging.

Update on the invasion status of the Argentine ant, Linepithema humile (Mayr, 1868), in Madrid, a large city in the interior of the Iberian Peninsula

New geolocated records of the invasive ant Linepithema humile (Mayr, 1868) are added to the previous references for the city of Madrid and its surroundings, and the possible causes of the occurrence and permanence of this species in urban areas are discussed. The data collection corresponds to a series of samplings carried out for the last three years in green areas of the city, bibliographic searches, citizen science platforms and personal communications. To date, eleven locations in the urban area of Madrid and four points outside the city have been registered. The city of Madrid is undergoing a colonisation by the Argentine ant, although it is not widespread yet, since observations over time and space are isolated and apparently unrelated. However, this species has a great capacity to disperse and establish new colonies, mainly human-mediated through the transport of goods, plants, gardening tools, etc. Considering the numerous colonizable urban green areas in the city that can provide the necessary conditions for its expansion, the Argentine ant should not be underestimated, and immediate action is strongly recommended.

Predictability of Invasive Argentine Ant Distribution Across Mediterranean Ecoregions of Southern California

The invasiveness of nonnative taxa can vary across a landscape due to environmental gradients, suggesting that location-dependent management strategies may be more effective at reducing spread compared to a “one size fits all” approach across the entire introduced range. Using bait stations placed along linear transects within habitat preserves, we tested for effects of ecoregion, vegetation, soil moisture, habitat edge type (i.e., moisture source), and distance from edges on the presence of the invasive Argentine ant Linepithema humile in San Diego County, California, a region with high indigenous biodiversity and numerous rare and protected species. Our results showed an inverse relationship between the presence of native ant species and the presence of the Argentine ant across ecoregions, with the latter reaching peak abundance in the coastal terrace. Argentine ant presence was negatively associated with distance from all edge types regardless of location, but the magnitude of this effect varied among ecoregions. In the xeric foothill and inland valleys, the probability of occurrence was nearly 0 at distances of 200 m and 750 m from moisture edges, respectively, whereas in the coastal terrace, the probability remained above 0.80 at distances up to 1.25 km. When compared to previous studies at different spatial scales, these findings provide an alternative perspective on the invasiveness of the Argentine ant at the landscape level. Our results further suggest that efforts to control spread in regions with a Mediterranean climate may be more successful in inland areas, where the ant is likely to have lower environmental tolerance and native ant species may be better able to generate biotic resistance. In contrast, different tactics and expectations may be necessary for coastal areas, where the same constraints are diminished or absent.

Environmental DNA detection of an invasive ant species (Linepithema humile) from soil samples

Alien ant species (Formicidae, Hymenoptera) cause serious damage worldwide. Early detection of invasion and rapid management are significant for controlling these species. However, these attempts are sometimes hindered by the need for direct detection techniques, such as capture, visual observation, or morphological identification. In this study, we demonstrated that environmental DNA (eDNA) analysis can be used as a monitoring tool for alien ants using Linepithema humile (Argentine ant), one of the most invasive ants, as a model species. We designed a new real-time PCR assay specific to L. humile and successfully detected eDNA from the surface soil. The reliability of eDNA analysis was substantiated by comparing eDNA detection results with traditional survey results. Additionally, we examined the relationship between eDNA concentration and distance from nests and trails. Our results support the effectiveness of eDNA for alien ant monitoring and suggest that this new method could improve our ability to detect invasive ant species.