Argentine Ant Research Articles

Mutualistic interactions facilitate invasive species spread

Abstract Invasive species are major drivers of global ecosystem change. They often displace native species through competitive exclusion, creating novel species interactions. These interactions can lead to ecological cascades, where the presence of one invasive species enhances the fitness of another. Despite this, the mechanisms that underpin these mutualistic interactions and promote secondary invasions remain poorly understood. We assessed how the introduction of the invasive Argentine ant (Linepithema humile) alters mutualistic interactions within the recipient community, enhancing the dispersal and fitness of species of a secondary invasive plant genus (Acacia spp.). Our study examines these interactions at the community, individual species, and trait levels for a range of native and non‐native ant and plant species. Specifically, we aimed to investigate the direct and indirect effects of L. humile on seed dispersal mutualisms. We found that in L. humile invaded locations, seeds of the invasive Acacia plant species were approximately three times more likely to be dispersed than seeds of native endemic plant species. This preference is driven by indirect changes in the community structure of native seed‐dispersing ants, rather than direct interactions between the invasive ant and plant species. Moreover, we found that native ant species that co‐exist with L. humile, such as Tetramorium sericeiventre, respond to a narrower range of seed traits—traits which the invasive Acacia seeds possess. Our findings suggest that the invasion of L. humile has cascading effects on ant‐plant mutualisms, potentially increasing community permeability to secondary invasions. These results highlight that the impact of invaders like the Argentine ant may be greater than initially perceived, driving losses in both biological and functional plant diversity. Read the free Plain Language Summary for this article on the Journal blog.

Common Home Remedies Do Not Deter Argentine Ants, Linepithema humile (Hymenoptera: Formicidae), from a Preferred Harborage.

In two laboratory trials, natural products, including freshly picked leaves from spearmint, rosemary, and tansy plants, a water extract from soybean plants, peels from a common cucumber, and 1% peppermint oil in hexane, were placed in a moist harborage preferred by Argentine ants, Linepithema humile (Mayr), and the number of ants entering the harborage after two and four hours was counted. None of the recommended home remedies (tansy, cucumber, or soybean extract) deterred ants from an attractive, moist harborage in either trial, even when the quantity of these treatments was increased 4- to 10-fold. Freshly picked leaves from rosemary and spearmint plants deterred ants from harboring, and the 1% peppermint oil was the most deterrent of all treatments.

The urban island: climatic suitability of Linepithema humile (Hymenoptera: Formicidae) and the role of cities in the invasion of the Western Palearctic

AbstractUrban environments often present environmental conditions that facilitate the introduction and establishment of nonnative and invasive species. These can expand their range into areas with unfavorable climates by taking advantage of the ecological and climatic homogenization of cities, bypassing the ecological barriers presented by the surrounding environment. One way to monitor the expansion of these species is using potential distribution models. We used as a model species the Argentine ant, Linepithema humile (Hymenoptera: Formicidae) whose invasion has caused serious consequences for biodiversity and economic losses worldwide. We used the average result of six different algorithms and used climatic variables and population density as a proxy for the urbanization level in the Western Palearctic to build the predictive model. The model indicates this ant prefers to inhabit areas with Mediterranean and Temperate Oceanic climates and that its suitability depends on two main factors: the continentality (temperature annual range) and the degree of urbanization. The species is predicted to be absent in areas with large temperature contrasts throughout the year, particularly in rural and peri‐urban areas (i.e. adjacent to urban areas) of inland regions. Conversely, the species has a predilection for coastal and urban areas where environmental conditions are attenuated by the influence of the sea or the “urban heat island” effect in the case of inland cities. In this sense, cities act as “bioclimatic islands” facilitating the establishment of the Argentine ant as a reservoir, enlarging its distribution into climatically nonoptimal areas, and promoting its future expansion in a scenario of global warming and socioeconomic change.

Fipronil-infused sodium polyacrylate gels provide effective management of Argentine ants in conservation areas.

Various types of hydrogel compounds have recently been developed for controlling invasive and pest ants in a range of environmental settings including agricultural, urban and natural areas. The current study evaluated the potential of sodium polyacrylate (ACR) hydrogels to effectively deliver liquid baits to Argentine ants. Relative to standard polyacrylamide (PAM) hydrogels, individual ACR hydrogel particles were approximately five-fold heavier; this may affect how ants interact with the bait particles, and further influence bait uptake and efficacy. Additionally, ACR hydrogels had significantly higher water absorption capacity and significantly slower rate of water loss, especially during the first 2 h. The efficacy of ACR hydrogel bait containing 0.005% fipronil and various attractants was evaluated on laboratory colonies. Results demonstrated that ACR hydrogel acceptance is significantly increased by the addition of feeding attractants. In addition, a field trial was performed in a nature reserve invaded by Argentine ants to evaluate the efficacy of ACR hydrogel bait. The field trial demonstrated that ACR hydrogel bait containing 0.005% fipronil with various attractants is highly effective and that ant densities throughout the baited plots declined by >99% within 7 days. The results of this study demonstrate that: (i) fipronil is highly effective for Argentine ant control in natural areas when used in low concentrations (0.005%); (ii) ACR hydrogels are an effective tool for delivering liquid baits to Argentine ants; and (iii) hydrogel baits augmented with various attractants including salt, protein and pheromone are highly attractive to Argentine ants. © 2024 The Author(s). Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Découverte de Linepithema humile (Mayr, 1868) sur l’île de la Réunion (France) et nouvelle mention pour l’espèce Cyphomyrmex minutus Mayr, 1862 avec inclusion géoréférencée des espèces rencontrées (Hymenoptera : Formicidae : Myrmicinae)

We report for the first time the presence of the Argentine ant Linepithema humile (Mayr, 1868) on Reunion Island and specify the conditions under which we detected it. We also mention the second observation for the ant Cyphomyrmex minutus Mayr, 1862.

Field evaluations of biodegradable boric acid hydrogel baits for the control of Argentine ants: Promising results in vineyards and citrus orchards

Argentine ants are a major pest in California. In this study, a biodegradable calcium alginate hydrogel with an aqueous boric acid bait was tested against Argentine ant populations in a citrus orchard and a vineyard. A new continuous method was developed to produce large quantities of hydrogel bait for the field test. Foraging activity levels of ants were compared between baited and untreated zones. For both study sites, four to five monthly bait applications throughout summer provided a greater than 80% reduction in ant activity. Based on spatial analyses by distance indices, the baited areas were characterized by gaps (areas with lower ant counts) and the untreated control zones were characterized by patches (areas with higher ant counts). This indicated area-wide suppression of Argentine ants. For the citrus orchard, post-baiting panel trap monitoring showed reductions of both ants and Asian citrus psyllid in the baited zone compared to the control. For the vineyard, mid-season soil analyses indicated that the impact of boric acid baiting on soil boron concentration was negligible. In sum, the calcium alginate hydrogel bait with boric acid as an active ingredient may provide a promising solution for Argentine ant baiting.

Variable viral loads and immune response in an invasive ant's native and introduced ranges

AbstractAimPathogens can play an important role in biological invasions. Introduced populations may be particularly vulnerable to pathogens due to factors such as low genetic diversity and high population density. However, introduced populations that escape their natural pathogens may reallocate resources away from immunity and towards growth and reproduction. Interestingly, introduced ants have been suggested to have increased tolerance to new pathogens, contributing to their success as introduced species. In this study, we aimed to investigate whether introduced Argentine ant populations harbour different viral loads compared to native populations and if these differences were related to immunity‐related gene expression.LocationThe study was conducted across the native range of Argentine ants in Argentina and four introduced regions in California, France, Australia and New Zealand.MethodsWe used RT‐qPCR to quantify viral loads and gene expression in the ants. We analysed 15 different potentially pathogenic viruses across the Argentine ant's native and introduced ranges.ResultsWe found that five viruses, LhuPcV1, LhuPiLV1, LhuCV1, Kashmir Bee virus and LHUV‐1, presented high loads in Argentine ants compared to the other viruses we screened. We found a significant effect of range on viral infections: high viral loads were commonly found in ants from introduced populations, which also exhibited increased immune gene expression. We found highly significant correlations between viral loads and expression of immune and metabolic genes. However, these associations were not fully consistent across the studied regions, indicating the complexity of eco‐immunological phenomena.Main ConclusionsOur results suggest that introduced Argentine ant populations host different viral communities compared to native populations and that these differences are correlated with changes in immunity‐related gene expression. The study highlights the complex role of pathogens in biological invasions and the importance of considering eco‐immunological factors when assessing the impact of introduced species.

Predicting Community Participation in Passive Pest Surveillance

Predicting the willingness of people to engage in passive surveillance is crucial to the success of community-based efforts to manage invasive species and conserve native biodiversity. We draw on the marketing concept of involvement, which reflects the personal importance of an issue or behaviour, to understand and measure the motivation of members of the public to engage in passive surveillance. The usefulness of this concept was tested by analysing the responses of householders to surveys about their willingness to engage in passive surveillance for a purely environmental pest, Red-eared Slider Turtles (Trachemys scripta elegans), and their willingness to engage in passive surveillance for an economic and environmental pest, Argentine Ants (Linepithema humile), in New Zealand. We found that involvement influenced intentions, attitudes and surveillance behaviour for both invasive pests. We discussed the implications of these findings for (i) choosing between a surveillance strategy based on recruiting and training highly motivated members of the public and a strategy based on passive surveillance by any member of the public; (ii) growing the potential for passive surveillance by either increasing involvement with preventing the spread of a pest or increasing involvement with surveillance activities themselves; and (iii) determining the importance of convenient reporting mechanisms in promoting consistent reporting.

Considering climate change impact on the global potential geographical distribution of the invasive Argentine ant and little fire ant.

The Argentine ant (Linepithema humile) and the little fire ant (Wasmannia auropunctata) are among the top 100 invasive alien species globally, causing significant ecological and economic harm. Therefore, it is crucial to study their potential geographic distribution worldwide. This study aimed to predict their global distribution under current and future climate conditions. We used distribution data from various sources, including CABI, GBIF, and PIAKey, and key climate variables selected from 19 environmental factors to model their potential geographic distribution using MaxEnt. The AUC values were 0.925 and 0.937 for L. humile and W. auropunctata, respectively, indicating good predictive performance. Suitable areas for L. humile were mainly in southern North America, northern South America, Europe, central Asia, southern Oceania, and parts of Africa, while W. auropunctata suitable areas were mostly in southern North America, most of South America, a small part of Europe, southern Asia, central Africa, and some parts of Oceania. Under climate change scenario, suitable areas for L. humile increased, while highly suitable areas for W. auropunctata decreased. The top four countries with the largest areas of overlapping suitable habitat under current climate were Brazil, China, Australia, and Argentina, while under future SSP585 climate scenario, the top four countries were Brazil, China, Indonesia, and Argentina. Some countries, such as Estonia and Finland, will see an overlapping adaptation area under climate change. In conclusion, this study provides insight into controlling the spread and harm of L. humile and W. auropunctata.

Toxicity-Related Behavior in the Invasive Argentine Ant Linepithema humile Mayr in Response to Fipronil Exposure1

Toxicity-Related Behavior in the Invasive Argentine Ant Linepithema humile Mayr in Response to Fipronil Exposure1

Do Dominant Native Ants Outcompete the Invasive Argentine Ant in Mediterranean Citrus Ecosystems? A Laboratory Test.

The invasive Argentine ant (Linepithema humile) poses a significant threat to ecosystem stability worldwide. In Mediterranean citrus ecosystems, its spread may be limited by interactions with dominant native ant species. We conducted laboratory experiments to investigate the competitive dynamics between Argentine ants and two major native species, Tapinoma nigerrimum and Lasius grandis. At the individual level, both native species exhibited superior competitive performance, attributed to their larger body sizes and potential differences in chemical defences. At the colony level, T. nigerrimum demonstrated efficiency in interference competition, successfully defending food resources from Argentine ants. However, the Argentine ant exhibited higher recruitment capacity, albeit it was density-dependent. Our findings support the hypothesis that dominant native ants can serve as barriers against Argentine ant invasion in citrus ecosystems, highlighting the importance of interspecific competition in shaping community dynamics and invasive species management. This study underscores the potential role of native ant species in mitigating the impacts of invasive ants on ecosystem functioning and biodiversity conservation in agricultural landscapes, offering valuable insights for invasive species management strategies in Mediterranean citrus ecosystems.

First record of the Argentine ant, Linepithema humile (Mayr, 1868) (Hymenoptera: Formicidae), from the Malagasy region

Summary The Argentine ant, Linepithema humile (Mayr, 1868), is a highly invasive species with serious detrimental consequences to native fauna and flora in invaded territories. Native to South-Central South America, it was first reported from continental Africa in 1893 but, to date, had never been recorded from the Malagasy region (encompassing Madagascar, Comoros, Seychelles, and Mascarene archipelago). Here, we report the first record of this invasive species on the island of La Réunion, a French overseas territory part of the Mascarene archipelago. The species was identified using both morphological and molecular analysis. We discuss potential ecological consequences of the presence of this ant on the insular ecosystems of La Réunion.

Alien Ants (Hymenoptera, Formicidae) in Sicily and Malta: A Review and Updated Checklist

In the last few years, due to globalization, which increases and speeds up the movement of people and goods around the world, the number of alien animal and plant species that have accidentally arrived in Europe has increased considerably; as a result, the problem of alien species, and especially invasive ones, has taken on greater significance. Since the Mediterranean has always been one of the main trade routes, it is of primary importance to turn our attention to those areas that constitute the main entry routes for new species into Italy and Europe, such as Sicily and the Maltese archipelago. This publication aims to collect all available data about alien invasive ants recorded in Sicily and Malta. Among all animal taxa, one of the groups with great adaptability and that easily follows human routes is the Formicidae, which also includes species with high invasive potential. Currently in Sicily there are 10 alien ant species, two of which, Linepithema humile (Mayr, 1878) and Solenopsis invicta Buren, 1972 (recently recorded), are invasive. Whereas for the Maltese archipelago 12 ant species are alien, two are considered invasives, namely L. humile and Pheidole indica Mayr, 1879. An additional species, Cardiocondyla mauritanica Forel, 1890, is considered cryptogenic in both countries. For a proper management of alien species, it is essential to carefully monitor the alien species already present on the territory and considered invasive but also to pay attention to those species that have already caused serious damage in other countries and are easy to introduce. Finally, it is important to monitor potential entry routes followed by invasive aliens, especially those involving interchanges between Sicily and the Maltese archipelago.

Corpse-associated odours elicit avoidance in invasive ants.

Invasive ants, such as Linepithema humile (the Argentine ant), pose a global threat, necessitating a better understanding of their behaviour in order to improve management strategies. Traditional eradication methods, including baiting, have had limited success, but the causes of control failure are not always clear. This study aims to investigate whether ants form associations between food odours and corpses, and subsequently avoid areas or food sources with food odours associated with corpses. We propose that ants may learn to avoid toxic baits in part because of their association with ant corpses, which could have implications for pest control strategies. Ants were tested on a Y-maze after exposure to scented corpses or dummies. 69% (n = 64) of ants avoided branches bearing the scent of scented corpses. Colonies neglected food with corpse-associated odours, with only 42% (n = 273) of foragers feeding from such sources. However, if corpses were produced by feeding ants scented toxicant, focal ants encountering these corpses did not avoid the corpse-associated scent on a Y-maze (53%, n = 65). In dual-feeder tests, ants did not avoid feeding at food sources scented with odours associated with conspecific corpses. Conspecific corpses act as a negative stimulus for ants in a foraging situation, potentially causing avoidance of toxic baits. This study suggests adding odours to baits and cycling them to disrupt the bait-corpse association may be helpful. Interestingly, although avoidance of baits was observed, feeding preferences were not significantly affected. © 2023 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Positive selection has shaped the evolution of Argentine ant immune genes both in native and introduced supercolonies.

The highly invasive Argentine ant (Linepithema humile) started its colonisation from the species' native range in South America approximately 150 years ago and has since become one of the major pests in the world. We investigated how the shifts into new ranges have affected the evolution of Argentine ants' immune genes. To the best of our knowledge, this is the first broadscale population genetic study focusing on ants' immune genes. We analysed comprehensive targeted-seq data of immune and non-immune genes containing 174 genes from 18 Argentine ant supercolonies covering the species' native and introduced ranges. We predicted that the immune gene evolution of introduced supercolonies differs from that of the native supercolonies and proposed two different, non-mutually exclusive hypotheses for this: 1) the enemy release hypothesis and 2) the higher pathogen pressure hypothesis - both of which seem to explain the observed evolutionary patterns on their behalf. Our results show that the introduced supercolonies were targeted by weaker selection than natives, but positive selection was evident among supercolonies of both ranges. Moreover, in some cases, such as the antiviral RNAi genes, introduced range supercolonies harboured a higher proportion of positively selected genes than natives. This observation was striking, knowing the recent demographic history and the detected generally lower selection efficacy of introduced supercolonies. In conclusion, it is evident that pathogen pressure is ubiquitous and strongly affects the immune gene evolution in Argentine ants.

Spinosad‐infused biodegradable hydrogel beads as a potential organic approach for argentine ant, Linepithema humile (Mayr) (hymenoptera: Formicidae), management in California citrus orchards

AbstractArgentine ant, Linepithema humile (Mayr), disrupts biological control services in California citrus orchards, leading to economically damaging densities of honeydew‐producing hemipteran pests. With the elimination of chlorpyrifos, the sole registered insecticide for L. humile control in California citrus, the development of effective alternatives is necessary. One alternative is aqueous sugar baits laced with minute concentrations (0.0001%) of insecticide. Field trials were conducted to assess the efficacy of spinosad and thiamethoxam‐infused alginate hydrogel beads (HGBs) for L. humile control. Thiamethoxam‐infused HGBs have previously shown high efficacy against L. humile in citrus. Spinosad is approved for organic use, while thiamethoxam, a neonicotinoid, along with other neonicotinoid insecticides, might soon face deregistration in California, underscoring the need for alternative insecticide chemistries for ant control. Therefore, this study aimed to optimize spinosad‐loaded HGBs by identifying efficacious concentrations, application rates, and deployment frequency, and to compare with thiamethoxam‐infused HGBs, the standard reference treatment. Results showed that spinosad‐infused HGBs significantly reduced high‐density L. humile populations in citrus orchards. Notably, the highest spinosad concentration tested (0.01%) demonstrated comparable control to both 0.0001% and 0.01% thiamethoxam concentrations. A tri‐weekly application schedule for spinosad‐infused HGBs provided best control. Trees treated with 125 or 250 g of hydrogels infused with 0.01% spinosad at weeks 0, 3, and 6 displayed significantly reduced ant activities compared to plots treated solely during weeks 0 and 6, as well as control plots lacking HGB applications. Spinosad‐infused HGBs may offer an effective alternative to thiamethoxam‐infused HGBs for control of L. humile in California citrus orchards.

They arrived and don’t stop coming: an update on the distribution of exotic ants (Hymenoptera, Formicidae) in continental Ecuador

We present an updated list of introduced ants to continental Ecuador, and compile records of occurrence, as well as map the distribution of 15 exotic species. We analyzed specimens in entomological collections and data from AntWeb, GBIF and iNaturalist. Among these, we add two new records for the country: Cardiocondyla mauritanica Forel, 1980 and Pheidole megacephala (Fabricius, 1793). The former is also the first record for South America, while the finding of the latter shows how little we know about introduced tramp ants. In addition, we add site records for nine species: Cardiocondyla emeryi Forel, 1881, Cardiocondyla minutior Forel, 1899, Cardiocon­dyla wroughtonii (Forel, 1890), Linepithema humile (Mayr, 1868), Monomorium floricola (Jerdon, 1851), Monomo­rium pharaonis (Linnaeus, 1758), Paratrechina longicornis (Latreille, 1802), Tapinoma melanocephalum (Fabricius, 1793), and Tetramorium bicarinatum (Nylander, 1846). Based on our previous fieldwork observations, it appears that our understanding of exotic species richness is still in its early stages.

Comparison of Argentine ant Linepithema humile (Hymenoptera: Formicidae) recruitment to hydrogel baits and other food sources

Comparison of Argentine ant Linepithema humile (Hymenoptera: Formicidae) recruitment to hydrogel baits and other food sources

Analysis of whole‐genome changes and characteristics of Linepithema humile (Hymenoptera: Formicidae) in the Republic of Korea

AbstractThe Argentine ant, Linepithema humile (Mayr, 1868), native to the Paraguay River in South America, was first discovered in Korea in 2019. With increasing reports of L. humile, its genetic variation according to domestic growth colonies and its effects on the domestic ecosystem should be studied. Here, the genomes of L. humile specimens found at three locations in Busan were analyzed for genetic changes. First, morphological observation of L. humile samples collected from the three sites showed no phenotypic differences among them. Next, single‐nucleotide polymorphism (SNP)/insertion and deletion (INDEL) analyses on the genomic DNA from the three groups showed that in the 1‐NIE sample, the most frequent mutations were G → A and C → T. The mutations A → C and T → G were confirmed in the 14‐NIE and 19‐NIE samples. Although the number of SNPs in the N section was small, sequences of 4681 bp (1‐NIE), 4217 bp (14‐NIE) and 4631 bp (19‐NIE) in length were identified. From the INDEL length distribution of the three samples, most changes were associated with insertions and deletions of 1–2 bp. However, no heterogeneity was found in the population samples analyzed based on SNP data. Comparative analysis of the SNPs investigated revealed that 760 819 (11.72%) of the total 6 492 517 SNPs were found in common, demonstrating that the three groups analyzed had different genetic backgrounds. Overall, we have developed a method for analyzing the genetic diversity of L. humile invading the Republic of Korea, precisely classified its genetic characteristics and obtained genomic data on interspecies mutations, according to the local environment.

ECR Spotlight - Brian Whyte.

ECR Spotlight is a series of interviews with early-career authors from a selection of papers published in Journal of Experimental Biology and aims to promote not only the diversity of early-career researchers (ECRs) working in experimental biology during our centenary year, but also the huge variety of animals and physiological systems that are essential for the 'comparative' approach. Brian Whyte is an author on ' The role of body size and cuticular hydrocarbons in the desiccation resistance of invasive Argentine ants (Linepithema humile)', published in JEB. Brian conducted the research described in this article while a PhD student in Neil Tsutsui's lab at the University of California, Berkeley, USA. He is now a postdoc in the lab of Abel Bernadou at the Research Center on Animal Cognition, Center for Integrative Biology, CNRS - Université Paul Sabatier, France, investigating how animals recognize friend from foe and other social categories.