Recent human history governs global ant invasion dynamics

Transoceanic pathogen transfer in the age of sail and steam

In the centuries following Christopher Columbus's 1492 voyage to the Americas, transoceanic travel opened unprecedented pathways in global pathogen circulation. Yet no biological transfer is a single, discrete event. We use mathematical modeling to quantify historical risk of shipborne pathogen introduction, exploring the respective contributions of journey time, ship size, population susceptibility, transmission intensity, density dependence, and pathogen biology. We contextualize our results using port arrivals data from San Francisco, 1850 to 1852, and from a selection of historically significant voyages, 1492 to 1918. We offer numerical estimates of introduction risk across historically realistic ranges of journey time and ship population size, and show that both steam travel and shipping regimes that involved frequent, large-scale movement of people substantially increased risk of transoceanic pathogen circulation.

Toxicity and Behavior-Altering Effects of Three Nanomaterials on Red Imported Fire Ants and Their Effectiveness in Combination with Indoxacarb

The red imported fire ant (Solenopsis invicta Buren) is one of the 100 worst invasive alien species in the world. At present, the control of red imported fire ants is still mainly based on chemical control, and the most commonly used is indoxacarb bait. In this study, the contact and feeding toxicity of 16 kinds of nanomaterials to workers, larvae, and reproductive ants were evaluated after 24 h, 48 h, and 72 h. The results showed that the mortality of diatomite, Silica (raspberry-shaped), and multi-walled carbon nanotubes among workers reached 98.67%, 97.33%, and 68%, respectively, after contact treatment of 72 h. The mortality of both larval and reproductive ants was less than 20% after 72 h of treatment. All mortality rates in the fed treatment group were below 20% after 72 h. Subsequently, we evaluated the digging, corpse-removal, and foraging behaviors of workers after feeding with diatomite, Silica (raspberry-shaped), and multi-walled carbon nanotubes for 24 h, which yielded inhibitory effects on the behavior of red imported fire ants. The most effective was diatomite, which dramatically decreased the number of workers that dug, extended the time needed for worker ant corpse removal and foraging activities, decreased the number of workers that foraged, and decreased the weight of the food carried by the workers. In addition, we also evaluated the contact and feeding toxicity of these three nanomaterials in combination with indoxacarb on red imported fire ants. According to contact toxicity, after 12 h of contact treatment, the death rate among the red imported fire ants exposed to the three materials combined with indoxacarb reached more than 97%. After 72 h of exposure treatment, the mortality rate of larvae was more than 73% when the nanomaterial content was above 1% and 83% when the diatomite content was 0.5%, which was significantly higher than the 50% recorded in the indoxacarb control group. After 72 h of feeding treatment, the mortality of diatomite, Silica (raspberry-shaped), and multi-walled carbon nanotubes combined with indoxacarb reached 92%, 87%, and 98%, respectively. The death rates of the three kinds of composite ants reached 97%, 67%, and 87%, respectively. The three kinds of composite food had significant inhibitory effects on the behavior of workers, and the trend was largely consistent with the effect of nanomaterials alone. This study provides technical support for the application of nanomaterials in red imported fire ant control.

Gut microbiota in parasite-transmitting gastropods

BACKGROUND

Gastropoda, the largest class within the phylum Mollusca, houses diverse gut microbiota, and some gastropods serve as intermediate hosts for parasites. Studies have revealed that gut bacteria in gastropods are associated with various biological aspects, such as growth, immunity and host-parasite interactions. Here, we summarize our current knowledge of gastropod gut microbiomes and highlight future research priorities and perspectives.

METHODS

A literature search was undertaken using PubMed, Web of Science and CNKI for the articles on the gut microbiota of gastropods until December 31, 2022. We retrieved a total of 166 articles and identified 73 eligible articles for inclusion in this review based on the inclusion and exclusion criteria.

RESULTS

Our analysis encompassed freshwater, seawater and land snails, with a specific focus on parasite-transmitting gastropods. We found that most studies on gastropod gut microbiota have primarily utilized 16S rRNA gene sequencing to analyze microbial composition, rather than employing metagenomic, metatranscriptomic, or metabolomic approaches. This comprehensive review provided an overview of the parasites carried by snail species in the context of gut microbiota studies. We presented the gut microbial trends, a comprehensive summary of the diversity and composition, influencing factors, and potential functions of gastropod gut microbiota. Additionally, we discussed the potential applications, research gaps and future perspectives of gut microbiomes in parasite-transmitting gastropods. Furthermore, several strategies for enhancing our comprehension of gut microbiomes in snails were also discussed.

CONCLUSIONS

This review comprehensively summarizes the current knowledge on the composition, potential function, influencing factors, potential applications, limitations, and challenges of gut microbiomes in gastropods, with a specific emphasis on parasite-transmitting gastropods. These findings provide important insights for future studies aiming to understand the potential role of gastropod gut microbiota in controlling snail populations and snail-borne diseases.

Termite cuticular extracts improve acceptance of bait for controlling invasive Asian needle ants, Brachyponera chinensis

BACKGROUND

The Asian needle ant, Brachyponera chinensis, is an invasive ant currently spreading in urban and natural habitats throughout the eastern United States. Recent studies have documented the negative impact of B. chinensis on native ecosystems and human health, yet effective control strategies are lacking. Control difficulties are, in part, due to the unique biology of B. chinensis, which is a predatory ant and a termite specialist. Given that subterranean termites are an important nutritional resource for B. chinensis, the current study evaluated the potential of termite cuticular extract to improve the target-specificity and efficacy of commercial bait used for B. chinensis control.

RESULTS

The efficacy of bait augmented with termite cuticular extracts was evaluated in laboratory and field trials. In laboratory assays, B. chinensis colonies were offered granular bait treated with termite cuticular extract. Results demonstrated that the acceptance of commercial bait is significantly increased by the addition of termite cuticular extract or synthetic (Z)-9-pentacosene, a major component of termite cuticular extract. Foraging activity of Asian needle ants was significantly greater on baits augmented with termite cuticular extract or (Z)-9-pentacosene relative to standard bait. Furthermore, bait augmented with termite cuticular extract worked substantially faster relative to standard bait. To evaluate population effects, field studies were conducted in forested areas invaded by B. chinensis. Bait treated with termite cuticular extract scattered on the forest floor provided rapid control of B. chinensis and ant densities throughout the treated plots declined by 98% within 14 days.

CONCLUSION

The incorporation of termite cuticular extracts and individual cuticular hydrocarbons such as (Z)-9-pentacosene into traditional baits used for B. chinensis control may offer a novel tool to manage this increasingly problematic invasive ant. © 2023 The Author. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Evolutionary imbalance, climate and human history jointly shape the global biogeography of alien plants

Human activities are causing global biotic redistribution, translocating species and providing them with opportunities to establish populations beyond their native ranges. Species originating from certain global regions, however, are disproportionately represented among naturalized aliens. The evolutionary imbalance hypothesis posits that differences in absolute fitness among biogeographic divisions determine outcomes when biotas mix. Here, we compile data from native and alien distributions for nearly the entire global seed plant flora and find that biogeographic conditions predicted to drive evolutionary imbalance act alongside climate and anthropogenic factors to shape flows of successful aliens among regional biotas. Successful aliens tend to originate from large, biodiverse regions that support abundant populations and where species evolve against a diverse backdrop of competitors and enemies. We also reveal that these same native distribution characteristics are shared among the plants that humans select for cultivation and economic use. In addition to influencing species' innate potentials as invaders, we therefore suggest that evolutionary imbalance shapes plants' relationships with humans, impacting which species are translocated beyond their native distributions.

Transcriptomic Analysis of Metarhizium anisopliae-Induced Immune-Related Long Non-Coding RNAs in Polymorphic Worker Castes of Solenopsis invicta

Long non-coding RNAs (lncRNAs) represent a class of RNA molecules that do not encode proteins. Generally studied for their regulatory potential in model insects, relatively little is known about their immunoregulatory functions in different castes of eusocial insects, including Solenopsis invicta, a notoriously invasive insect pest. In the current study, we used Metarhizium anisopliae, an entomopathogenic fungus, to infect the polymorphic worker castes (Major and Minor Workers) and subjected them to RNA sequencing at different intervals (6, 24, and 48 h post-infection (hpi)). Comprehensive bioinformatic analysis identified 5719 (1869 known and 3850 novel) lncRNAs in all libraries. Genomic characteristics analysis showed that S. invicta lncRNAs exhibited structural similarities with lncRNAs from other eusocial insects, including lower exon numbers, shorter intron and exon lengths, and a lower expression profile. A comparison of lncRNAs in major and minor worker ants revealed that several lncRNAs were exclusively expressed in one worker caste and remained absent in the other. LncRNAs such as MSTRG.12029.1, XR_005575440.1 (6 h), MSTRG.16728.1, XR_005575440.1 (24 h), MSTRG.20263.41, and MSTRG.11994.5 (48 h) were only present in major worker ants, while lncRNAs such as MSTRG.8896.1, XR_005574239.1 (6 h), MSTRG.20289.8, XR_005575051.1 (24 h), MSTRG.20289.8, and MSTRG.6682.1 (48 h) were only detected in minor workers. Additionally, we performed real-time quantitative PCR and experimentally validated these findings. Functional annotation of cis-acting lncRNAs in major worker ants showed that lncRNAs targeted genes such as serine protease, trypsin, melanization protease-1, spaetzle-3, etc. In contrast, apoptosis and autophagy-related genes were identified as targets of lncRNAs in minor ants. Lastly, we identified several lncRNAs as precursors of microRNAs (miRNAs), such as miR-8, miR-14, miR-210, miR-6038, etc., indicating a regulatory relationship between lncRNAs, miRNAs, and mRNAs in antifungal immunity. These findings will serve as a genetic resource for lncRNAs in polymorphic eusocial ants and provide a theoretical basis for exploring the function of lncRNAs from a unique and novel perspective.

Historical plant introductions predict current insect invasions

Thousands of insect species have been introduced outside of their native ranges, and some of them strongly impact ecosystems and human societies. Because a large fraction of insects feed on or are associated with plants, nonnative plants provide habitat and resources for invading insects, thereby facilitating their establishment. Furthermore, plant imports represent one of the main pathways for accidental nonnative insect introductions. Here, we tested the hypothesis that plant invasions precede and promote insect invasions. We found that geographical variation in current nonnative insect flows was best explained by nonnative plant flows dating back to 1900 rather than by more recent plant flows. Interestingly, nonnative plant flows were a better predictor of insect invasions than potentially confounding socioeconomic variables. Based on the observed time lag between plant and insect invasions, we estimated that the global insect invasion debt consists of 3,442 region-level introductions, representing a potential increase of 35% of insect invasions. This debt was most important in the Afrotropics, the Neotropics, and Indomalaya, where we expect a 10 to 20-fold increase in discoveries of new nonnative insect species. Overall, our results highlight the strong link between plant and insect invasions and show that limiting the spread of nonnative plants might be key to preventing future invasions of both plants and insects.

Behavioral assays reveal mechanisms of supercolony formation in odorous house ants

The formation of expansive multi-nest and multi-queen supercolonies is perhaps the most important factor responsible for the ecological success of invasive ants. The odorous house ant, Tapinoma sessile, is a widespread ant native to North America. T. sessile is a challenging urban pest, but also serves as an interesting system to study ant social organization and invasion biology. This is due to its remarkable dichotomy in colony social and spatial structure between natural and urban environments. Natural colonies typically consist of a small number of workers, inhabit a single nest, and are monogyne whereas urban colonies show extreme polygyny and polydomy and form large supercolonies. The current study examined the extent to which T. sessile colonies from different habitats (natural vs. urban) and social structures (monogynous vs. polygynous) exhibit aggression toward alien conspecifics. Additionally, interactions between mutually aggressive colonies were examined in colony fusion experiments to assess the potential role of colony fusion as a mechanism leading to supercolony formation. Aggression assays demonstrated high levels of aggression in pairings involving workers from different urban colonies and workers from different natural colonies, but low aggression in pairings involving queens from different urban colonies. Colony merging tests demonstrated that urban T. sessile colonies are highly aggressive to each other, but capable of fusing under laboratory conditions when competing for limited nesting and food resources. Despite highly aggressive interactions and relatively high worker and queen mortality, all colony pairs merged in 3-5 days. Fusion occurred after most workers died and the survivors merged. This result suggests that the success of T. sessile in urban areas may be driven, at least in part, by successful colony mergers of unrelated colonies which may be determined by ecological constraints such as seasonal shortages in nest and/or food availability. In summary, two independent factors including the growth of a single colony and/or the merger of multiple colonies may be responsible for the evolution of supercolonies in invasive ants. Both processes may be happening simultaneously and may act synergistically to produce supercolonies.

Biological invasions: The secret domination of alien ants

Globalization has contributed to the spread of thousands of species, yet only a few harmful ones have attracted most attention. New evidence shows that introduced ants are a particularly important group of global invaders that can dominate native insect communities.

Six decades of museum collections reveal disruption of native ant assemblages by introduced species

There is a looming environmental crisis characterized by widespread declines in global biodiversity,^1,2,3,4,5,6 coupled with the establishment of introduced species at accelerated rates.^{7,8,9,10,11,12,13,14} We quantified how multi-species invasions affect litter ant communities in natural ecosystems by leveraging museum records and contemporary collections to assemble a large (18,990 occurrences, 6,483 sampled local communities, and 177 species) 54-year (1965-2019) dataset for the entire state of Florida, USA. Nine of ten species that decreased most strongly in relative abundance ("losers") were native, while nine of the top ten "winners" were introduced species. These changes led to shifts in the composition of rare and common species: in 1965, only two of the ten most common ants were introduced, whereas by 2019, six of ten were introduced species. Native losers included seed dispersers and specialist predators, suggesting a potential loss of ecosystem function through time, despite no obvious loss of phylogenetic diversity. We also examined the role of species-level traits as predictors of invasion success. Introduced species were more likely to be polygynous than native species. The tendency to form supercolonies, where workers from separate nests integrate, also differed between native and introduced species and was correlated with the degree to which species increased in their rank abundances over 50 years. In Florida, introduced ants now account for 30% of occurrence records, and up to 70% in southern Florida. If current trends continue, introduced species will account for over half of occurrence records in all Florida's litter ant communities within the next 50 years.

Niche Filling Dynamics of Ragweed (Ambrosia artemisiifolia L.) during Global Invasion

Determining whether the climatic ecological niche of an invasive alien plant is similar to that of the niche occupied by its native population (ecological niche conservatism) is essential for predicting the plant invasion process. Ragweed (Ambrosia artemisiifolia L.) usually poses serious threats to human health, agriculture, and ecosystems within its newly occupied range. We calculated the overlap, stability, unfilling, and expansion of ragweed's climatic ecological niche using principal component analysis and performed ecological niche hypothesis testing. The current and potential distribution of A. artemisiifolia was mapped by ecological niche models to identify areas in China with the highest potential risk of A. artemisiifolia invasion. The high ecological niche stability indicates that A. artemisiifolia is ecologically conservative during the invasion. Ecological niche expansion (expansion = 0.407) occurred only in South America. In addition, the difference between the climatic and native niches of the invasive populations is mainly the result of unpopulated niches. The ecological niche model suggests that southwest China, which has not been invaded by A. artemisiifolia, faces an elevated risk of invasion. Although A. artemisiifolia occupies a climatic niche distinct from native populations, the climatic niche of the invasive population is only a subset of the native niche. The difference in climatic conditions is the main factor leading to the ecological niche expansion of A. artemisiifolia during the invasion. Additionally, human activities play a substantial role in the expansion of A. artemisiifolia. Alterations in the A. artemisiifolia niche would help explain why this species is so invasive in China.

Genetic analysis reveals the putative native range and widespread double-clonal reproduction in the invasive longhorn crazy ant

Clonal reproduction can provide an advantage for invasive species to establish as it can circumvent inbreeding depression which often plagues introduced populations. The world's most widespread invasive ant, Paratrechina longicornis, was previously found to display a double-clonal reproduction system, whereby both males and queens are produced clonally, resulting in separate male and queen lineages, while workers are produced sexually. Under this unusual reproduction mode, inbreeding is avoided in workers as they carry hybrid interlineage genomes. Despite the ubiquitous distribution of P. longicornis, the significance of this reproductive system for the ant's remarkable success remains unclear, as its prevalence is still unknown. Further investigation into the controversial native origin of P. longicornis is also required to reconstruct the evolutionary histories of double-clonal lineages. Here, we examine genetic variation and characterize the reproduction mode of P. longicornis populations sampled worldwide using microsatellites and mitochondrial DNA sequences to infer the ant's putative native range and the distribution of the double-clonal reproductive system. Analyses of global genetic variations indicate that the Indian subcontinent is a genetic diversity hotspot of this species, suggesting that P. longicornis probably originates from this geographical area. Our analyses revealed that both the inferred native and introduced populations exhibit double-clonal reproduction, with queens and males around the globe belonging to two separate, nonrecombining clonal lineages. By contrast, workers are highly heterozygous because they are first-generation interlineage hybrids. Overall, these data indicate a worldwide prevalence of double clonality in P. longicornis and support the prediction that the unusual genetic system may have pre-adapted this ant for global colonization by maintaining heterozygosity in the worker force and alleviating genetic bottlenecks.

Population Genomics for Insect Conservation

Insects constitute vital components of ecosystems. There is alarming evidence for global declines in insect species diversity, abundance, and biomass caused by anthropogenic drivers such as habitat degradation or loss, agricultural practices, climate change, and environmental pollution. This raises important concerns about human food security and ecosystem functionality and calls for more research to assess insect population trends and identify threatened species and the causes of declines to inform conservation strategies. Analysis of genetic diversity is a powerful tool to address these goals, but so far animal conservation genetics research has focused strongly on endangered vertebrates, devoting less attention to invertebrates, such as insects, that constitute most biodiversity. Insects' shorter generation times and larger population sizes likely necessitate different analytical methods and management strategies. The availability of high-quality reference genome assemblies enables population genomics to address several key issues. These include precise inference of past demographic fluctuations and recent declines, measurement of genetic load levels, delineation of evolutionarily significant units and cryptic species, and analysis of genetic adaptation to stressors. This enables identification of populations that are particularly vulnerable to future threats, considering their potential to adapt and evolve. We review the application of population genomics to insect conservation and the outlook for averting insect declines.

Insights into insecticide-resistance mechanisms in invasive species: Challenges and control strategies

Threatening the global community is a wide variety of potential threats, most notably invasive pest species. Invasive pest species are non-native organisms that humans have either accidentally or intentionally spread to new regions. One of the most effective and first lines of control strategies for controlling pests is the application of insecticides. These toxic chemicals are employed to get rid of pests, but they pose great risks to people, animals, and plants. Pesticides are heavily used in managing invasive pests in the current era. Due to the overuse of synthetic chemicals, numerous invasive species have already developed resistance. The resistance development is the main reason for the failure to manage the invasive species. Developing pesticide resistance management techniques necessitates a thorough understanding of the mechanisms through which insects acquire insecticide resistance. Insects use a variety of behavioral, biochemical, physiological, genetic, and metabolic methods to deal with toxic chemicals, which can lead to resistance through continuous overexpression of detoxifying enzymes. An overabundance of enzymes causes metabolic resistance, detoxifying pesticides and rendering them ineffective against pests. A key factor in the development of metabolic resistance is the amplification of certain metabolic enzymes, specifically esterases, Glutathione S-transferase, Cytochromes p450 monooxygenase, and hydrolyses. Additionally, insect guts offer unique habitats for microbial colonization, and gut bacteria may serve their hosts a variety of useful services. Most importantly, the detoxification of insecticides leads to resistance development. The complete knowledge of invasive pest species and their mechanisms of resistance development could be very helpful in coping with the challenges and effectively developing effective strategies for the control of invasive species. Integrated Pest Management is particularly effective at lowering the risk of chemical and environmental contaminants and the resulting health issues, and it may also offer the most effective ways to control insect pests.

The worldwide networks of spread of recorded alien species

Our ability to predict the spread of alien species is largely based on knowledge of previous invasion dynamics of individual species. However, in view of the large and growing number of alien species, understanding universal spread patterns common among taxa but specific to regions would considerably improve our ability to predict future dynamics of biological invasions. Here, using a comprehensive dataset of years of first record of alien species for four major biological groups (birds, nonmarine fishes, insects, and vascular plants), we applied a network approach to uncover frequent sequential patterns of first recordings of alien species across countries worldwide. Our analysis identified a few countries as consistent early recorders of alien species, with many subsequent records reported from countries in close geographic vicinity. These findings indicate that the spread network of alien species consists of two levels, a backbone of main dispersal hubs, driving intercontinental species movement, and subsequent intracontinental radiative spread in their vicinity. Geographical proximity and climatic similarity were significant predictors of same-species recording among countries. International trade was a significant predictor of the relative timing of species recordings, with countries having higher levels of trade flows consistently recording the species earlier. Targeting the countries that have emerged as hubs for the early spread of alien species may have substantial cascading effects on the global spread network of alien species, significantly reducing biological invasions. Furthermore, using these countries as early-warning system of upcoming invasions may also boost national prevention and invasion preparedness efforts.

Spatial Distribution Pattern and Risk Assessment of Invasive Alien Plants on Southern Side of the Daba Mountain Area

The southern side of the Daba Mountain area is a hotspot of global biodiversity and an essential barrier promoting ecological security. However, knowledge about the distribution status and transmission pathways of invasive alien species (IAS) in this area is limited. We counted the IAS on the southern side of the Daba Mountain area through sample transects and analyzed the factors affecting their spatial distribution. We also assessed IAS risk using the analytic hierarchy process (AHP), which found 64 IAS belonging to 23 families and 53 genera. Around rivers and roads, the results showed a vertical two-way dispersal pattern. Human and environmental factors, such as a very dense transportation network, can affect the distribution pattern of IAS. AHP assessed 43 IAS (67.19%), primarily distributed in villages and towns, as being of high or medium risk. High- and medium-risk IAS should be the focus of invasion prevention and control, and priority should be given to controlling the spread of IAS around rivers and roads.

Simulation the potential distribution of Dendrolimus houi and its hosts, Pinus yunnanensis and Cryptomeria fortunei, under climate change in China

Due to climate change, it is significant to explore the impact of rising temperatures on the distribution of Dendrolimus houi Lajonquiere (Lepidoptera) and its host plants, Pinus yunnanensis and Cryptomeria fortunei, and to simulate their suitable future distribution areas in order to provide a theoretical basis for the monitoring of, and early warning about, D. houi and the formulation of effective prevention and control policies. Based on the known distribution areas of, and relevant climate data for, D. houi, P. yunnanensis, and C. fortunei, their suitable habitat in China was predicted using the ENMeval data package in order to adjust the maximum entropy (MaxEnt) model parameters. The results showed that the regularization multiplier was 0.5 when the feature combination was LQHPT, with a MaxEnt model of lowest complexity and excellent prediction accuracy. The main climate variable affecting the geographical distribution of D. houi, P. yunnanensis, and C. fortunei is temperature, specifically including isothermality, temperature seasonality, maximum temperature of warmest month, minimum temperature of warmest month, average temperature of coldest quarter. The potential suitable distribution areas for P. yunnanensis and D. houi were similar under climate change, mainly distributed in southwest China, while C. fortunei was mainly distributed in southeast China. Under different future-climate scenarios, the areas suitable for the three species will increase, except for P. yunnanensis in the 2070s under Shared Socioeconomic Pathway 5-8.5. With climate change, all three species were found to have a tendency to migrate to higher latitudes and higher altitudes. The centroids of the areas suitable for P. yunnanensis and D. houi will migrate to the northwest and the centroids of the areas suitable for C. fortunei will migrate to the northeast.

Efficiency of ant-control agents in colony-level oral toxicity tests using Tetramorium tsushimae (Hymenoptera: Formicidae) for post-establishment control of the red imported fire ant, Solenopsis invicta (Hymenoptera: Formicidae)

The red imported fire ant Solenopsis invicta Buren (Hymenoptera: Formicidae) causes serious damage worldwide as an invasive alien species. The species has expanded its range to the Pacific Rim since 2000s and Japan has faced its multiple introductions since 2017. While colony-level control methods are urgently needed, testing living colonies of the unestablished species is challenging especially due to various restrictions under the COVID-19 pandemic. Here, we proposed alternative long-term toxicity assays using artificial colonies of Tetramorium tsushimae Emery (Hymenoptera: Formicidae), a Japanese native species belonging to the same subfamily (Myrmicinae) as S. invicta. We conducted an acute toxicity test to determine if T. tsushimae is a suitable substitute for S. invicta using fipronil and found the LD₅₀ value in T. tsushimae was close to that in S. invicta. Then, we conducted the long-term toxicity test with fipronil and two insect growth regulators (pyriproxyfen and etoxazole) using artificial colonies of T. tsushimae. All workers and larvae in the fipronil-treated colonies died within 3 days of treatment initiation. Emergence of new workers was observed after 18 days in the etoxazole-treated and control colonies, but not in the pyriproxyfen-treated colonies. We concluded that fipronil was the most promising insecticide for post-establishment control, and pyriproxyfen was effective as a toxic-bait agent for colony-level control.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s13355-022-00800-x.

Resilience of native ant community against invasion of exotic ants after anthropogenic disturbances of forest habitats

The positive association between disturbances and biological invasions is a widely observed ecological pattern in the Anthropocene. Such patterns have been hypothesized to be driven by the superior competitive ability of invaders or by modified environments, as well as by the interaction of these factors. An experimental study that tests these hypotheses is usually less feasible, especially in protected nature areas. An alternative approach is to focus on community resilience over time after the anthropogenic disturbance of habitats. Here, we focused on ant communities within a forest to examine their responses after disturbance over time. We selected the Yanbaru region of northern Okinawa Island, which is a biodiversity hotspot in East Asia. We compared ant communities among roadside environments in forests where the road age differed from 5 to 25 years. We also monitored the ant communities before and after disturbance from forest thinning. We found that the species richness and abundance of exotic ants were higher in recently disturbed environments (roadsides of 5-15 years old roads), where the physical environment was warmer and drier. In contrast, the roadsides of 25-year-old roads indicated the potential recovery of the physical environment with cooler and moister conditions, likely owing to regrowth of roadside vegetation. At these sites, there were few exotic ants, except for those immediately adjacent to the road. The population density of the invasive species Technoymex brunneus substantially increased 1-2 years after forest thinning. There was no evidence of the exclusion of native ants by exotic ants that were recorded after disturbance. Our results suggest that local ant communities in the Yanbaru forests have some resilience to disturbance. We suggest that restoration of environmental components is a better strategy for maintaining native ant communities, rather than removing exotic ants after anthropogenic disturbance.

A global review of socioeconomic and environmental impacts of ants reveals new insights for risk assessment

Risk assessments are fundamental to invasive species management and are underpinned by comprehensive characterization of invasive species impacts. Our understanding of the impacts of invasive species is growing constantly, and several recently developed frameworks offer the opportunity to systematically categorize environmental and socioeconomic impacts of invasive species. Invasive ants are among the most widespread and damaging invaders. Although a handful of species receives most of the policy attention, nearly 200 species have established outside their native range. Here, we provide a global, comprehensive assessment of the impacts of ants and propose a priority list of risk species. We used the Socioeconomic Impact Classification for Alien Taxa (SEICAT), Environmental Impact Classification for Alien Taxa (EICAT) and Generic Impact Scoring System (GISS) to analyze 642 unique sources for 100 named species. Different methodologies provided generally consistent results. The most frequently identified socioeconomic impacts were to human health. Environmental impacts were primarily on animal and plant populations, with the most common mechanisms being predation and competition. Species recognized as harmful nearly 20 years ago featured prominently, including Wasmannia auropunctata (little fire ant, electric ant), Solenopsis invicta (red imported fire ant), Anoplolepis gracilipes (yellow crazy ant), and Pheidole megacephala (African big-headed ant). All these species except W. auropunctata have been implicated in local extinctions of native species. Although our assessments affirmed that the most serious impacts have been driven by a small number of species, our results also highlighted a substantial number of less well publicized species that have had major environmental impacts and may currently be overlooked when prioritizing prevention efforts. Several of these species were ranked as high or higher than some of the previously recognized "usual suspects," most notably Nylanderia fulva (tawny crazy ant). We compared and combined our assessments with trait-based profiles and other lists to propose a consensus set of 31 priority species. Ever-increasing global trade contributes to growing rates of species introductions. The integrated approaches we used can contribute to robust, holistic risk assessments for many taxa entrained in these pathways.

Economic costs of invasive alien ants worldwide

Invasive ants are amongst the most destructive and widespread invaders across the globe; they can strongly alter invaded ecosystems and are responsible for the loss of native ant species. Several studies have reported that invasive ants can also lead to substantial economic costs. In this study, we search, describe and analyse 1342 reported costs of invasive ants compiled in the InvaCost database. Economic costs, reported since 1930 for 12 ant species in 27 countries, totalled US$ 51.93 billion, from which US$ 10.95 billion were incurred, and US$ 40.98 billion were potential costs (i.e., expected or predicted costs). More than 80% of total costs were associated with only two species, Solenopsis invicta and Wasmannia auropunctata; and two countries, the USA and Australia. Overall, damage costs amounted to 92% of the total cost, mainly impacting the agriculture, public and social welfare sectors. Management costs were primarily post-invasion management (US$ 1.79 billion), with much lower amounts dedicated to prevention (US$ 235.63 million). Besides the taxonomic bias, cost information was lacking for an average of 78% of the invaded countries. Moreover, even in countries where costs were reported, such information was available for only 56% of the invaded locations. Our synthesis suggests that the global costs of invasive ants are massive but largely biased towards developed economies, with a huge proportion of underreported costs, and thus most likely grossly underestimated. We advocate for more and improved cost reporting of invasive ants through better collaborations between managers, practitioners and researchers, a crucial basis for adequately informing future budgets and improving proactive management actions of invasive ants.

Comprehensive Detoxification Mechanism Assessment of Red Imported Fire Ant (Solenopsis invicta) against Indoxacarb

The red imported fire ant (Solenopsis invicta) is one of the deadliest invasive ant species that threatens the world by disrupting biodiversity, important functions within a natural ecosystem, and community structure. They are responsible for huge economic losses in the infested countries every year. Synthetic insecticides, especially indoxacarb, have been broadly used to control S. invicta for many years. However, the biochemical response of S. invicta to indoxacarb remains largely undiscovered. Here, we used the sublethal doses of indoxacarb on the S. invicta collected from the eight different cities of Southern China. The alteration in the transcriptome profile of S. invicta following sublethal dosages of indoxacarb was characterized using high-throughput RNA-seq technology. We created 2 libraries, with 50.93 million and 47.44 million clean reads for indoxacarb treatment and control, respectively. A total of 2018 unigenes were regulated after insecticide treatment. Results indicated that a total of 158 differentially expressed genes (DEGs) were identified in the indoxacarb-treated group, of which 100 were significantly upregulated and 58 were downregulated, mostly belonging to the detoxification enzymes, such as AChE, CarE, and GSTs. Furthermore, results showed that most of these DEGs were found in several KEGG pathways, including steroid biosynthesis, other drug metabolizing enzymes, glycerolipid metabolism, chemical carcinogenesis, drug-metabolizing cytochrome P450, glutathione metabolism, glycerophospholipid metabolism, glycolysis/gluconeogenesis, and metabolism of xenobiotics. Together, these findings indicated that indoxacarb causes significant alteration in the transcriptome profile and signaling pathways of S. invicta, providing a foundation for further molecular inquiry.

The global loss of floristic uniqueness

Regional species assemblages have been shaped by colonization, speciation and extinction over millions of years. Humans have altered biogeography by introducing species to new ranges. However, an analysis of how strongly naturalized plant species (i.e. alien plants that have established self-sustaining populations) affect the taxonomic and phylogenetic uniqueness of regional floras globally is still missing. Here, we present such an analysis with data from native and naturalized alien floras in 658 regions around the world. We find strong taxonomic and phylogenetic floristic homogenization overall, and that the natural decline in floristic similarity with increasing geographic distance is weakened by naturalized species. Floristic homogenization increases with climatic similarity, which emphasizes the importance of climate matching in plant naturalization. Moreover, floristic homogenization is greater between regions with current or past administrative relationships, indicating that being part of the same country as well as historical colonial ties facilitate floristic exchange, most likely due to more intensive trade and transport between such regions. Our findings show that naturalization of alien plants threatens taxonomic and phylogenetic uniqueness of regional floras globally. Unless more effective biosecurity measures are implemented, it is likely that with ongoing globalization, even the most distant regions will lose their floristic uniqueness.

Improved Light Traps for Early Detection of Insect Pests of Phytosanitary Concern in Shipping Containers

The number of introductions of alien insect has been increasing in the last decades, primarily transported in shipping containers. The attraction of light of different wavelengths (white, infrared, ultraviolet, and red) applied on sticky traps was tested for the development of new traps for hitchhiker insects. The addition of entomological glue and insecticide on the trap was also tested. Tests were conducted on Cadra cautella Walker (Lepidoptera: Pyralidae), Drosophila melanogaster Meigen (Diptera: Drosophilidae), Sitophilus zeamais Motschulsky (Coleoptera: Curculionidae), and Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae) and released inside a shipping container. In the first test, one light color at a time was tested setting eight traps in the container, one for each possible combination of the variables: light on or off, glue added or not, and insecticide sprayed or not. In the second, five traps were used, all of them coated with the entomological glue: one for each light color and one with light off as control. In all the single color tests (except for infrared), light-on traps captured more, except for T. castaneum that was not attracted to white. In the multi-color test, C. cautella showed no preference among white, ultraviolet, or red; Drosophila melanogaster preferred ultraviolet and white over red; and beetles had a much greater attraction to red. Lastly, the stronger entomological glue improved catches of beetles, whereas insecticides did not. In conclusion, results suggest a possible application of sticky light traps against hitchhiker insects and further studies should verify if the simultaneous use of different light colors can improve the trap performance and does not act as a repellent.

Non-kin Cooperation in Ants

Eusociality represents an extreme form of social behavior characterized by a reproductive division of labor. Eusociality necessarily evolved through kin selection, which requires interactions among related individuals. However, many eusocial taxa also show cooperation between non-kin groups, challenging the idea that cooperative actions should only occur among relatives. This review explores the causes and consequences of non-kin cooperation in ants. Ants display a diversity of behaviors that lead to non-kin cooperation within and between species. These interactions occur among both reproductive and non-reproductive individuals. The proximate and ultimate mechanisms leading to non-kin cooperative interactions differ substantially depending on the biotic and abiotic environment. We end this review with directions for future research and suggest that the investigation of non-kin cooperative actions provides insight into processes leading to social evolution.

Impact of invasive ant species on native fauna across similar habitats under global environmental changes

Biotic invasions can predominantly alter the dynamics, composition, functions, and structure of natural ecosystems. Social insects, particularly ants, are among the most damaging invasive alien species. Invasive ant species are among the supreme threats to ecosystems. There are about 23 species of invasive ants recorded worldwide, according to the ant invasive databases. The ecological impacts of invasive ants comprise predation, hybridization, and competition with native species that changes the ecosystem processes with the biodiversity loss and upsurge of pests. The effects of invasion on native fauna in the same habitats might be catastrophic for the native community through various ecological mechanisms, e.g., habitat disturbance, resource competition, limiting the foraging activity of native species, and various other indirect mechanisms of invasive species. Invasive species may have harmful impacts on habitats and devastating effects on natural flora and fauna, and stopping these new species from being introduced is the most effective way to deter future invasions and maintain biodiversity. This paper reviews the literature to evaluate the effects of invasive ant species on the native species, including vertebrates, invertebrates, and plants sharing the same habitats as the non-native species under global environmental changes. We also highlighted the various management strategies that could be adopted in minimizing the adverse effects of these invasive ant species on the natural ecosystem. To this end, strategies that could regulate the mode and rate of invasion by these alien ant species are the most effective ways to deter future invasions and maintain biodiversity.

Consistent signatures of urban adaptation in a native, urban invader ant Tapinoma sessile

Biological invasions are becoming more prevalent due to the rise of global trade and expansion of urban areas. Ants are among the most prolific invaders with many exhibiting a multiqueen colony structure, dependent colony foundation and reduced internest aggression. Although these characteristics are generally associated with the invasions of exotic ants, they may also facilitate the spread of native ants into novel habitats. Native to diverse habitats across North America, the odorous house ant Tapinoma sessile has become abundant in urban environments throughout the United States. Natural colonies typically have a small workforce, inhabit a single nest, and are headed by a single queen, whereas urban colonies tend to be several orders of magnitude larger, inhabit multiple nests (i.e., polydomy) and are headed by multiple queens (i.e., polygyny). Here, we explore and compare the population genetic and breeding structure of T. sessile within and between urban and natural environments in several localities across its distribution range. We found the social structure of a colony to be a plastic trait in both habitats, although extreme polygyny was confined to urban habitats. Additionally, polydomous colonies were only present in urban habitats, suggesting T. sessile can only achieve supercoloniality within urbanized areas. Finally, we identified strong differentiation between urban and natural populations in each locality and continent-wide, indicating cities may restrict gene flow and exert intense selection pressure. Overall, our study highlights urbanization's influence in charting the evolutionary course for species.

Predicting the potential global distribution of Ageratina adenophora under current and future climate change scenarios

AIM

Invasive alien species (IAS) threaten ecosystems and humans worldwide, and future climate change may accelerate the expansion of IAS. Predicting the suitable areas of IAS can prevent their further expansion. Ageratina adenophora is an invasive weed over 30 countries in tropical and subtropical regions. However, the potential suitable areas of A. adenophora remain unclear along with its response to climate change. This study explored and mapped the current and future potential suitable areas of Ageratina adenophora.

LOCATION

Global.

TAXA

Asteraceae A. adenophora (Spreng.) R.M.King & H.Rob. Commonly known as Crofton weed.

METHODS

Based on A. adenophora occurrence data and climate data, we predicted its suitable areas of this weed under current and future (four RCPs in 2050 and 2070) by MaxEnt model. We used ArcGIS 10.4 to explore the potential suitable area distribution characteristics of this weed and the "ecospat" package in R to analyze its altitudinal distribution changes.

RESULTS

The area under the curve (AUC) value (>0.9) and true skill statistics (TSS) value (>0.8) indicated excelled model performance. Among environment factors, mean temperature of coldest quarter contributed most to the model. Globally, the suitable areas for A. adenophora invasion decreased under climate change scenarios, although regional increases were observed, including in six biodiversity hotspot regions. The potential suitable areas of A. adenophora under climate change would expand in regions with higher elevation (3,000-3,500 m).

MAIN CONCLUSIONS

Mean temperature of coldest quarter was the most important variable influencing the potential suitable area of A. Adenophora. Under the background of a warming climate, the potential suitable area of A. adenophora will shrink globally but increase in six biodiversity hotspot regions. The potential suitable area of A. adenophora would expand at higher elevation (3,000-3,500 m) under climate change. Mountain ecosystems are of special concern as they are rich in biodiversity and sensitive to climate change, and increasing human activities provide more opportunities for IAS invasion.

Insect and plant invasions follow two waves of globalisation

Globalisation has facilitated the spread of alien species, and some of them have significant impacts on biodiversity and human societies. It is commonly thought that biological invasions have accelerated continuously over the last centuries, following increasing global trade. However, the world experienced two distinct waves of globalisation (~1820–1914, 1960‐present), and it remains unclear whether these two waves have influenced invasion dynamics of many species. To test this, we built a statistical model that accounted for temporal variations in sampling effort. We found that insect and plant invasion rates did not continuously increase over the past centuries but greatly fluctuated following the two globalisation waves. Our findings challenge the idea of a continuous acceleration of alien species introductions and highlight the association between temporal variations in trade openness and biological invasion dynamics. More generally, this emphasises the urgency of better understanding the subtleties of socio‐economic drivers to improve predictions of future invasions.

Globalization and the anthropogenic spread of invasive social insects

Social insects are among the worst invasive species and a better understanding of their anthropogenic spread is needed. I highlight recent research demonstrating that social insects have been dispersed since the early beginnings of globalized trade and in particular after the Industrial Revolution, following two waves of globalization. Many species have complex invasion histories, with multiple independent introduction events and frequent secondary spread. The major source and recipient regions differ markedly across ants, wasps, termites and bees, probably linked to their different introduction pathways. At a more local scale, anthropogenic factors such as irrigation, urbanization or the presence of railways facilitate invasions. In the future, social insect invasions could further accelerate due to intensifying global trade and novel introduction pathways.

Breeding structure and invasiveness in social insects

Plasticity in life history traits is commonly used to explain the invasion success of social insects. While intraspecific plasticity is often recognized, interspecific variability is easily overlooked, whereby different species exhibit different strategies. The presence of many queens per colony and the collapse of colony boundaries have favored invasiveness for many ant species. However, these strategies are absent from other successful social invaders. Here, we report that various life-history traits may differentially enhance the invasion success in social insects. We suggest that other aspects of their breeding system, like asexual reproduction, intranidal mating and pre-adaptation to inbreeding may enhance their invasion success. Thorough comparative studies between native and introduced populations or studies of closely related species will help identify additional traits favoring the invasion success of social insects, and ultimately provide a more comprehensive picture of the evolutionary factors enhancing invasiveness across this phylogenetically and ecologically diverse group.

Contrasting responses of native ant communities to invasion by an ant invader, Linepithema humile

Invasive alien species pose a serious threat to the integrity and function of natural ecosystems. Understanding how these invaders alter natural communities is therefore an important aspect in predicting the likely future outcomes of biological invasions. Many studies have documented the consequences of invasive alien species on native community structure, through the displacement and local extinction of native species. However, sampling methods and intensities are rarely standardised across such studies, meaning that it is not clear whether differences in response among native communities to the same invader species are due to biological differences between the invaded regions, or differences in the methodologies used. Here we use a matched sampling methodology to compare the effects of the Argentine ant (Linepithema humile Mayr) on native ant community assemblages in two distinct biogeographical regions that share similar ecologies: Girona (Spain) and Jonkershoek Nature Reserve (South Africa). We found a strong negative association between L. humile presence and native ant species richness within both geographic regions. However, the effects differed between the two study regions: in Girona, a single native ant species (Plagiolepis pygmaea) persisted in invaded sites; by contrast, substantially more native ant species persisted at invaded sites in Jonkershoek Nature Reserve. In addition, in Jonkershoek Nature Reserve, the abundance of certain native species appeared to increase in the presence of L. humile. This study therefore demonstrates the potential variable effects of an invasive species in contrasting locations within different biogeographical regions. Future work should explore the causes of this differential resistance among communities and expand standardised sampling approaches to more invaded zones to further explore how local biotic or abiotic conditions of a region determine the nature and extent of impact of L. humile invasion on native ant communities.

How does climate change affect social insects?

Climate change poses a major threat to global biodiversity, already causing sharp declines of populations and species. In some social insect species we already see advanced phenologies, changes in distribution ranges, and changes in abundance Rafferty (2017) and Diamond et al. (2017). Physiologically, social insects are no different from solitary insects, but they possess a number of characteristics that distinguish their response to climate change. Here, we examine these traits, which might enable them to cope better with climate change than solitary insects, but only in the short term. In addition, we discuss how climate change will alter biotic interactions and ecosystem functions, and how it will affect invasive social insects.

Extensive human-mediated jump dispersal within and across the native and introduced ranges of the invasive termite Reticulitermes flavipes

As native ranges are often geographically structured, invasive species originating from a single source population only carry a fraction of the genetic diversity present in their native range. The invasion process is thus often associated with a drastic loss of genetic diversity resulting from a founder event. However, the fraction of diversity brought to the invasive range may vary under different invasion histories, increasing with the size of the propagule, the number of reintroduction events, and/or the total genetic diversity represented by the various source populations in a multiple-introduction scenario. In this study, we generated a SNP data set for the invasive termite Reticulitermes flavipes from 23 native populations in the eastern United States and six introduced populations throughout the world. Using population genetic analyses and approximate Bayesian computation random forest, we investigated its worldwide invasion history. We found a complex invasion pathway with multiple events out of the native range and bridgehead introductions from the introduced population in France. Our data suggest that extensive long-distance jump dispersal appears common in both the native and introduced ranges of this species, probably through human transportation. Overall, our results show that similar to multiple introduction events into the invasive range, admixture in the native range prior to invasion can potentially favour invasion success by increasing the genetic diversity that is later transferred to the introduced range.

Effect of social structure and introduction history on genetic diversity and differentiation

Invasive species are a global threat to biodiversity, and understanding their history and biology is a major goal of invasion biology. Population-genetic approaches allow insights into these features, as population structure is shaped by factors such as invasion history (number, origin and age of introductions) and life-history traits (e.g., mating system, dispersal capability). We compared the relative importance of these factors by investigating two closely related ants, Tetramorium immigrans and Tetramorium tsushimae, that differ in their social structure and invasion history in North America. We used mitochondrial DNA sequences and microsatellite alleles to estimate the source and number of introduction events of the two species, and compared genetic structure among native and introduced populations. Genetic diversity of both species was strongly reduced in introduced populations, which also differed genetically from native populations. Genetic differentiation between ranges and the reduction in microsatellite diversity were more severe in the more recently introduced and supercolonial T. tsushimae. However, the loss of mitochondrial haplotype diversity was more pronounced in T. immigrans, which has single-queen colonies and was introduced earlier. Tetramorium immigrans was introduced at least twice from Western Europe to North America and once independently to South America. Its monogyny might have limited genetic diversity per introduction, but new mutations and successive introductions over a long time may have added to the gene pool in the introduced range. Polygyny in T. tsushimae probably facilitated the simultaneous introduction of several queens from a Japanese population to St. Louis, USA. In addition to identifying introduction pathways, our results reveal how social structure can influence the population-genetic consequences of founder events.

Chemical detection triggers honey bee defense against a destructive parasitic threat

Invasive species events related to globalization are increasing, resulting in parasitic outbreaks. Understanding of host defense mechanisms is needed to predict and mitigate against the consequences of parasite invasion. Using the honey bee Apis mellifera and the mite Varroa destructor, as a host-parasite model, we provide a comprehensive study of a mechanism of parasite detection that triggers a behavioral defense associated with social immunity. Six Varroa-parasitization-specific (VPS) compounds are identified that (1) trigger Varroa-sensitive hygiene (VSH, bees' key defense against Varroa sp.), (2) enable the selective recognition of a parasitized brood and (3) induce responses that mimic intrinsic VSH activity in bee colonies. We also show that individuals engaged in VSH exhibit a unique ability to discriminate VPS compounds from healthy brood signals. These findings enhance our understanding of a critical mechanism of host defense against parasites, and have the potential to apply the integration of pest management in the beekeeping sector.

Invasiveness is linked to greater commercial success in the global pet trade

The pet trade has become a multibillion-dollar global business, with tens of millions of animals traded annually. Pets are sometimes released by their owners or escape, and can become introduced outside of their native range, threatening biodiversity, agriculture, and health. So far, a comprehensive analysis of invasive species traded as pets is lacking. Here, using a unique dataset of 7,522 traded vertebrate species, we show that invasive species are strongly overrepresented in trade across mammals, birds, reptiles, amphibians, and fish. However, it is unclear whether this occurs because, over time, pet species had more opportunities to become invasive, or because invasive species have a greater commercial success. To test this, we focused on the emergent pet trade in ants, which is too recent to be responsible for any invasions so far. Nevertheless, invasive ants were similarly overrepresented, demonstrating that the pet trade specifically favors invasive species. We show that ant species with the greatest commercial success tend to have larger spatial distributions and more generalist habitat requirements, both of which are also associated with invasiveness. Our findings call for an increased risk awareness regarding the international trade of wildlife species as pets.

Genomic Signature of Shifts in Selection in a Subalpine Ant and Its Physiological Adaptations

Understanding how organisms adapt to extreme environments is fundamental and can provide insightful case studies for both evolutionary biology and climate-change biology. Here, we take advantage of the vast diversity of lifestyles in ants to identify genomic signatures of adaptation to extreme habitats such as high altitude. We hypothesized two parallel patterns would occur in a genome adapting to an extreme habitat: 1) strong positive selection on genes related to adaptation and 2) a relaxation of previous purifying selection. We tested this hypothesis by sequencing the high-elevation specialist Tetramorium alpestre and four other phylogenetically related species. In support of our hypothesis, we recorded a strong shift of selective forces in T. alpestre, in particular a stronger magnitude of diversifying and relaxed selection when compared with all other ants. We further disentangled candidate molecular adaptations in both gene expression and protein-coding sequence that were identified by our genome-wide analyses. In particular, we demonstrate that T. alpestre has 1) a higher level of expression for stv and other heat-shock proteins in chill-shock tests and 2) enzymatic enhancement of Hex-T1, a rate-limiting regulatory enzyme that controls the entry of glucose into the glycolytic pathway. Together, our analyses highlight the adaptive molecular changes that support colonization of high-altitude environments.

Temperature-dependent development and survival of an invasive genotype of wheat curl mite, Aceria tosichella

Quantifying basic biological data, such as the effects of variable temperatures on development and survival, is crucial to predicting and monitoring population growth rates of pest species, many of which are highly invasive. One of the most globally important pests of cereals is the eriophyoid wheat curl mite (WCM), Aceria tosichella, which is the primary vector of several plant viruses. The aim of this study was to evaluate temperature-dependent development and survival of WCM at a wide range of constant temperatures in the laboratory (17-33 °C). The development time of each stage depended significantly on temperature and it was negatively correlated with temperature increase. At high temperatures (27-33 °C), individuals had shorter developmental times, with the shortest (6 days) at 33 °C, whereas at the lowest tested temperatures (17-19 °C), developmental time was almost 3× longer. Moreover, temperature had a clear effect on survival: the higher the temperature, the lower the survival rate. These data provide information promoting more efficient and effective manipulation of WCM laboratory colonies, and further our understanding of the ramifications of temperature change on WCM physiology and implications for the growth and spread of this globally invasive pest.

Mutualism disruption by an invasive ant reduces carbon fixation for a foundational East African ant-plant

Invasive ants shape assemblages and interactions of native species, but their effect on fundamental ecological processes is poorly understood. In East Africa, Pheidole megacephala ants have invaded monodominant stands of the ant-tree Acacia drepanolobium, extirpating native ant defenders and rendering trees vulnerable to canopy damage by vertebrate herbivores. We used experiments and observations to quantify direct and interactive effects of invasive ants and large herbivores on A. drepanolobium photosynthesis over a 2-year period. Trees that had been invaded for ≥ 5 years exhibited 69% lower whole-tree photosynthesis during key growing seasons, resulting from interaction between invasive ants and vertebrate herbivores that caused leaf- and canopy-level photosynthesis declines. We also surveyed trees shortly before and after invasion, finding that recent invasion induced only minor changes in leaf physiology. Our results from individual trees likely scale up, highlighting the potential of invasive species to alter ecosystem-level carbon fixation and other biogeochemical cycles.

Influence of the Number of Queens on Nest Establishment: Native and Invasive Ant Species

As a critical stage in the life cycle of ant colonies, nest establishment depends on external and internal factors. This study investigates the effect of the number of queens on queen and worker behavior during nest establishment in invasive Argentine ants (Linepitema humile) and native Mediterranean Tapinoma nigerrimum. We set up experimental colonies with the same number of workers but with one or six queens. At different time points, we recorded the positions of queens and workers inside and outside the nest. Our results highlight the influence of the number of queens on the position of queens and workers with between-species differences. Queens of both species entered the nests more quickly when there were six queens. During nest establishment, more workers were inside nests with six queens for both species, with this effect being greater for T. nigerrimum. Once nests were established, fewer workers of both species were engaged in nest maintenance and feeding in nests with six queens; T. nigerrimum had fewer workers engaged in patrolling. These results suggest that the number of queens is a key factor driving queen and worker behavior during and after nest establishment with different species responses.

Introduced ant species occupy empty climatic niches in Europe

Exploring shifts in the climatic niches of introduced species can provide significant insight into the mechanisms underlying the invasion process and the associated impacts on biodiversity. We aim to test the phylogenetic signal hypothesis in native and introduced species in Europe by examining climatic niche similarity. We examined data from 134 ant species commonly found in western Europe; 130 were native species, and 4 were introduced species. We characterized their distribution patterns using species records from different databases, determined their phylogenetic relatedness, and tested for a phylogenetic signal in their optimal climatic niches. We then compared the introduced species' climatic niches in Europe with their climatic niches in their native ranges and with the climatic niches of their closest relative species in Europe. We found a strong phylogenetic signal in the optimal climatic niches of the most common ant species in Europe; however, this signal was weak for the main climatic variables that affect the distributions of introduced versus native species. Also, introduced species occupied different climatic niches in Europe than in their native ranges; furthermore, their European climatic niches did not resemble those of their closest relative species in Europe. We further discovered that there was not much concordance between the climatic niches of introduced species in their native ranges and climatic conditions in Europe. Our findings suggest that phylogenetics do indeed constrain shifts in the climatic niches of native European ant species. However, introduced species would not face such constraints and seemed to occupy relatively empty climatic niches.