Aggression in imported fire ants: an explanation for shifts in their spatial distributions in Southern United States?

Abstract 1. The imported fire ants, Solenopsis invicta Buren (red), S. richteri Forel (black), and their hybrids (S. invicta × S. richteri) are sympatric congeners with overlapping but shifting spatial distributions in northern Alabama and Mississippi, United States. 2. The abilities of workers of the three ant forms (or species) to recognise non‐nestmate conspecifics and heterospecifics were compared in separate aggression bioassays using three group sizes of competitor numbers (battles): 1‐1, 5‐1, and 5‐5 resident–intruder battles. 3. Workers of all three forms showed significant aggression toward non‐nestmate conspecifics and heterospecifics. The results of the intra‐specific aggression bioassays showed that S. invicta had the lowest aggression threshold, whereas S. richteri was the least aggressive. Survival rates 1 day after intra‐specific encounters were higher for S. richteri than for S. invicta or hybrids, consistent with its lower aggressiveness. 4. In inter‐specific interactions, S. invicta workers showed the greatest aggression and were more aggressive towards S. richteri than to hybrids. Furthermore, survival 1 day after inter‐specific encounters was highest for S. invicta workers, whether they were the intruders or residents. The hybrid form was intermediate between both parental forms in aggression and post‐aggression survival. 5. The live 1‐1 and 5‐5 battles produced similar and consistent results, but differences were amplified in the 5‐5 battles, suggesting an effect of group size on aggression. These results may explain the observed shifts in the spatial distributions of the three forms and range restriction of S. richteri in southern United States.     

Host preference in Pseudacteon phorid flies: response of P. tricuspis and P. curvatus to black, red and hybrid imported Solenopsis fire ants in multiple choice bioassays

Host preferences in both sexes of Pseudacteon tricuspis Borgmeier (Jaguariuna biotype) and Pseudacteon curvatus Borgmeier (Formosa biotype) and their relative attraction to the imported fire ants (IFA), Solenopsis invicta Buren (red IFA), Solenopsis richteri Forel (black IFA) and S. invicta × S. richteri hybrids (hybrid IFA) were investigated in two separate experiments utilizing multiple choice flight bioassays. The results of both experiments clearly showed that both sexes of the Jaguariuna biotype of P. tricuspis could distinguish among the three IFA species and demonstrated greater preference for hybrid IFA and red IFA. This conclusion is supported by a variety of data collected on the number of fly visits, attack rate, and hovering duration (Experiment 1), and on the number of trapped flies (Experiment 2), which showed that black IFA is the least preferred of the three species. Similar results were recorded for the Formosan biotype of P. curvatus, although the data were not as strongly conclusive. Females of this biotype spent a significantly greater amount of time in hovering mode over red IFA and hybrid IFA compared to black IFA, but the other data were not significant. The red IFA is the natural host of both phorid fly biotypes and our results suggest that both biotypes may have evolved a specialized relationship with red IFA including an ability to discriminate it from related fire ants. These results are discussed in relation to the possible role of fire ant chemicals in mediating host preferences in phorid flies, contributions of male phorid flies to fire ant biocontrol, and the practical implications of the key findings.     

Reproduction by virgin queen fire ants in queenless colonies: Comparative study of three taxa (Solenopsis richteri,hybridS. invicta/richteri,S. geminata) (Hymenoptera: Formicidae)

Summary In the fire ant,Solenopsis invicta, some winged virgin queens are known to shed their wings (dealate) upon removal of the mated mother queen. These virgin queens then develop their ovaries and begin to lay eggs, thereby foregoing the option of leaving on mating flights and attempting to found their own colonies. Such a response of virgin queens to queenlessness has not been reported for other ants. In order to determine if virgin queens of some other fire ants (subgenusSolenopsis) would respond in the same way, experiments were conducted onS. richteri, hybridS. invicta/richteri andS. geminata, a member of a species complex different from that of the other taxa. Just as inS. invicta, virgin queens ofS. richteri and the hybrid dealated and began to lay eggs within days of the removal of the queen. In addition, workers executed many of the reproductively active virgin queens, a phenomenon also found inS. invicta. In contrast, virgin queens ofS. geminata did not dealate or quickly begin to lay eggs upon separation from the queen. Reasons for the variability in the response of virgin queens of the different species may be 1) higher probability of reproductive success for unmated dealated queens compared to normal claustral founding inS. invicta andS. richteri linked to relatively frequent loss of the mother queen; or 2) phylogenetic constraint.     

COMPARATIVE BIOCHEMICAL GENETICS OF THREE FIRE ANT SPECIES IN NORTH AMERICA,WITH SPECIAL REFERENCE TO THE TWO SOCIAL FORMS OF SOLENOPSIS INVICTA (HYMENOPTERA: FORMICIDAE)

An electrophoretic study of the genetics of three fire ant species in North America was undertaken with the primary objective of further clarifying the genetic relationship between two social forms of Solenopsis invicta. Such social forms are common in many groups of ants and may, in some cases, represent significant intermediate stages in the speciation process. The monogyne and polygyne forms of S. invicta, while differing in a number of important biological traits, are genetically indistinguishable, in contrast to the substantial genetic differentiation observed between S. invicta and a second, closely related, introduced species, S. richteri. The native fire ant, S. geminata, is genetically the most distinct of the three species studied, in accord with its taxonomic placement in a different species complex. Hypotheses concerning the derivation of the polygyne form of S. invicta from the monogyne form which invoke their long-term reproductive isolation in South America and separate introductions to North America appear unfounded. Although S. invicta and S. richteri are known to hybridize in North America, our study provided no evidence of gene introgression between S. invicta and the native species, S. geminata, in areas where our samples were collected. Analyses of population structure in S. invicta failed to reveal significant differentiation of populations or local inbreeding. Levels of genetic diversity in the three species studied, although not significantly different, were in the order predicted from knowledge of the population biology and recent history of the taxa, with S. richteri exhibiting the least diversity, S. geminata the greatest, and S. invicta having an intermediate level.     

Chemical tools to distinguish the fire ant species Solenopsis invicta and S. saevissima (Formicidae: Myrmicinae) in Southeast Brazil

Morphologically similar fire ants Solenopsis invicta and Solenopsis saevissima are broadly sympatric in southeastern Brazil. Chemistry from venom (2,6-dialkyl piperidine alkaloids) and cuticular hydrocarbons have been reported as potentially important tools for differentiating Solenopsis species. We have analysed two chemical classes in widely separated populations of S. invicta and S. saevissima and find that both piperidine alkaloids and cuticular hydrocarbons separate the two species. Piperidine alkaloids clustered S. invicta but not S. saevissima. Cuticular hydrocarbons strongly clustered both S. invicta and S. saevissima. One population morphologically identified as S. invicta presented piperidine alkaloids and cuticular hydrocarbons markedly different from either species. The distinctive piperidine alkaloid differences among populations of S. saevissima and the marked difference in piperidine alkaloid and hydrocarbon profiles of the anomalous population of S. invicta suggest undescribed species fire ant in southeastern Brazil.     

New Family,Genus, and Species of Microsporida (Protozoa: Microsporida) from the Tropical Fire Ant,Solenopsis geminata (Fabricius) (Insecta: Formicidae)*

SYNOPSIS. A new species of Microsporida, Burenella dimorpha sp. n., representing a new family, Burenellidae fam. n. and genus, is described on the basis of light- and electron-microscope observations. The family is characterized by 2 sequences of sporogony, each sequence having morphologically different sporonts and spores. The parasite infects the tropical fire ant, Solenopsis geminata (Fabricius), producing distinct pathologic manifestations (clearing of the cuticle and eye malformation) and death in the pupal stage of development. Transmission of the infection per os to healthy S. geminata, to the Southern fire ant, Solenopsis xyloni McCook, and to the red and black imported fire ants, Solenopsis invicta Buren and Solenopsis richteri Forel, is reported.     

Molecular diversity of PBAN family peptides from fire ants

The PBAN/Pyrokinin peptide family is a major neuropeptide family characterized with a common FXPRLamide in the C‐termini. These peptides are ubiquitously distributed in the Insecta and are involved in many essential endocrinal functions, e.g., pheromone production. Previous work demonstrated the localization of PBAN in the fire ant central nervous system, and identified a new family of PBAN from the red imported fire ant, Solenopsis invicta. In this study, we identified five more PBAN/Pyrokinin genes from S. geminata, S. richteri, S. pergandii, S. carolinensis, and a hybrid of S. invicta and S. richteri. The gene sequences were used to determine the phylogenetic relationships of these species and hybrid, which compared well to the morphologically defined fire ant subgroup complexes. The putative PBAN and other peptides were determined from the amino acid sequences of the PBAN/pyrokinin genes. We summarized all known insect PBAN family neuropeptides, and for the first time constructed a phylogenetic tree based on the full amino acid sequences translated from representative PBAN cDNAs. The PBAN/pyrokinin gene is well conserved in Insecta and probably extends into the Arthropod phylum; however, translated pre‐propeptides may vary and functional diversity may be retained, lost, or modified during the evolutionary process. Published 2010 Wiley Periodicals, Inc.     

CYTONUCLEAR THEORY FOR HAPLODIPLOID SPECIES AND X-LINKED GENES. II. STEPPING-STONE MODELS OF GENE FLOW AND APPLICATION TO A FIRE ANT HYBRID ZONE

We develop cytonuclear, hybrid zone models for haplodiploid species or X-linked genes in diploid species using a stepping-stone framework of migration, in which migration rates vary with both direction and sex. The equilibrium clines for the allele frequencies, cytonuclear disequilibria, and frequencies of pure parental types are examined for species with diagnostic markers, under four important migration schemes: uniform migration of both sexes in both directions, greater migration of both sexes from one direction, greater migration of females, and greater migration of males. Of the three cytonuclear variables examined, the allele frequency clines are the most informative in differentiating among the various migration patterns. The cytonuclear disequilibria and the frequency of the pure parental types tend to be useful only in revealing directional asymmetries in migration. The extent of hybrid zone subdivision has quantitative but not qualitative effects on the distribution of cytonuclear variables, in that the allele frequency clines become more gradual, the cytonuclear disequilibria decrease in magnitude, and the frequencies of pure parentals decline with increasing subpopulation number. Also, the only major difference between the X-linked and haplodiploid frameworks is that a higher frequency of pure parentals is found when considering haplodiploids, in which male production does not require mating. The final important theoretical result is that censusing after migration yields greater disequilibria and parental frequencies than censusing after mating. We analyzed cytonuclear data from two transects from a naturally occurring hybrid zone between two haplodiploid fire ant species, Solenopsis invicta and S. richteri, using our stepping-stone framework. The frequency of S. invicta mtDNA exceeds the frequency of the S. invicta nuclear markers through much of this hybrid zone, indicating that sex differences in migration or selection may be occurring. Maximum-likelihood estimates for the migration rates are very high, due to an unexpectedly large number of pure parental types in the hybrid zone, and differ substantially between the two transects. Overall, our model does not provide a good fit, in part because the S. invicta–S. richteri hybrid zone has not yet reached equilibrium.     

SYSTEMATICS AND POPULATION GENETICS OF FIRE ANTS (SOLENOPSIS SAEVISSIMA COMPLEX) FROM ARGENTINA

Specimens of seven fire ant species collected from their native ranges in Argentina were studied by protein electrophoresis and morphological analysis. Concordance between the genetic and morphological character sets is strong (96% agreement on identifications), suggesting that recognition of reproductively isolated populations and partitioning of intra- and interspecific variation can in most cases be achieved using appropriate characters of either type in this taxonomically difficult group. Genetic differentiation between native (Argentina) and introduced (USA) conspecific populations of two species, Solenopsis invicta and S. richteri, is rather typical of the differentiation existing between conspecific populations found within either country. Furthermore, there appears to have been little reduction of variability (heterozygosity) at enzyme loci following colonization by either species of the United States, although some rare alleles have been lost in the introduced populations. Hybridization is rare between S. invicta and S. richteri where their native ranges overlap in central Argentina, in contrast to the extensive hybridization of these species in the United States, suggesting that prezygotic barriers to gene flow have been compromised in introduced populations. Phylogenetic analysis of the seven species indicates that S. invicta and S. richteri are relatively distantly related within the S. saevissima complex. Given that hybrids between these species in the United States suffer little apparent loss of fitness, genomic incompatibilities generally may be insufficient to create effective postzygotic barriers to interspecific gene flow in this group of ants.     

Predicted range expansion of the invasive fire ant, Solenopsis invicta, in the eastern United States based on the VEMAP global warming scenario

The red imported fire ant, Solenopsis invicta Buren, is an invasive pest from South America that currently occupies much of the south‐eastern USA. Global warming is likely to allow range expansion of many invasive species, including S. invicta. We used a dynamic, ecophysiological model of fire ant colony growth coupled with models simulating climate change to predict the potential range expansion of S. invicta in the eastern USA over the next century. The climate change scenario predicted by the Vegetation–Ecosystem Modelling and Analysis Project (VEMAP) was used in our analyses. Our predictions indicate that the habitable area for S. invicta may increase by c. 5% over the next 40–50 years (a northward expansion of 33 ± 35 km). As the pace of global warming is expected to quicken in the latter half of the century, however, the habitable area for S. invicta in 2100 is predicted to be > 21% greater than it currently is (a northward expansion of 133 ± 68 km). Because the black imported fire ant, S. richteri Forel, occupies higher latitudes than S. invicta, the overall area of the eastern USA infested with invasive Solenopsis species could be greater than that estimated here.     

Potential cause of lethality of an allele implicated in social evolution in fire ants

The gene Gp-9 is believed to have a major effect on colony social organization in fire ants, with the presence of b-like alleles in a colony associated with multiple-queen (polygyne) organization. Queens and workers of polygyne Solenopsis invicta homozygous for the b-like allele designated b suffer reduced viability compared to other genotypes, and bb queens do not survive to become egg-layers. Thus, the b allele effectively acts as a recessive lethal. This allele differs from the remaining b-like alleles (designated b′), as well as all other Gp-9 alleles, by encoding a lysine at position 151 in the protein product, suggesting that this substitution is responsible for its deleterious effects. We tested this hypothesis by comparing frequencies of b′b′ and bb homozygotes, first in queens of Solenopsis richteri and S. invicta, then in S. invicta workers from populations polymorphic for the two b-like alleles. We found that almost 20% of S. richteri queens were b′b′ homozygotes, compared to the virtual absence of bb homozygotes among S. invicta queens, and that 5–18% of S. invicta workers bore genotype b′b′, compared to the apparent lack of bb workers in the same populations. While we cannot entirely rule out involvement of other genes in complete gametic disequilibrium with Gp-9, our data are consistent with the hypothesis that the Lys¹⁵¹ residue in GP-9 protein confers the deleterious effects of the b allele in homozygous condition, possibly by impairing the protein’s function through interference with ligand binding/release or hindrance of dimer formation.     

Ontogeny of the Defensive Stinging Behavior of the Fire Ant, Solenopsis invicta

The fire ant, Solenopsis invicta, appears to deviate from the usual age-related pattern of defensive behavior seen in other social insects; instead of older workers being more defensive than younger ones, they are less so. Here I test this pattern by quantifying changes in the defensive stinging behavior of S. invicta workers of known age. I found defensiveness, measured as both the number of stings delivered and the amount of venom delivered per sting (venom dose), to increase with age initially but then decline after a mid-age peak. This hump-shaped ontogeny may be the result of S. invicta's foraging strategy, which effectively shifts the responsibility of nest defense to workers younger than foraging age. It is S. invicta's mid-aged workers that are the most defensive, probably because they are both physiologically and spatially the most suitable nest defenders.     

Potential Global Range Expansion of the Invasive Fire Ant, Solenopsis invicta

The red imported fire ant, Solenopsis invicta Buren, is an invasive pest that has become widespread in the southern United States and Caribbean after introduction from South America in the 1930s. This species, which has diverse detrimental impacts on recipient communities, was recently discovered in Australia and New Zealand and has the potential to colonize numerous other regions. We used a dynamic, ecophysiological model of colony growth to predict the potential global range expansion of this invasive species. Based on minimum and maximum daily temperatures, the model estimates colony alate production and predicts future geographic range limits. Because S. invicta populations are limited by arid conditions as well as cold temperatures, we superimposed precipitation data upon temperature-based predictions, to identify regions that do not receive enough rainfall to support this species across the landscape. Many areas around the globe, including large portions of Europe, Asia, Africa, Australia, and numerous island nations, are at risk for S. invicta infestation. Quarantine officials should be vigilant for any accidental introductions of this pest in susceptible regions. Costs of eradication increase dramatically as the area of infestation grows, and large infestations may be impossible to eradicate. Other South American Solenopsis fire ants (e.g., S. richteri Forel) may become invasive if the opportunity arises, and our predictions for S. invicta may approximate the potential range limits for these species as well.     

Phorid parasitoids affect foraging activity of Solenopsis richteri under different availability of food in Argentina

1. In Argentina, six species of Pseudacteon parasitoids (Phoridae) attack Solenopsis richteri, one of the two species of South American fire ant that are exotic pests in North America. 2. The presence of these Pseudacteon species significantly reduces the number of ants at food resources in the field, as well as foraging activity generally. 3. Some Pseudacteon not only attack ants walking on trails or at feeding sites, but also at mound entrances, inhibiting workers from leaving to forage. 4. The average size of foraging ants (which prescribes their suitability as hosts) decreased in the presence of phorids. 5. The number of attacking phorids was correlated positively with the number of ants walking towards the food on the trail before the attack. 6. Solenopsis richteri workers responded to manipulations of food size and presence or absence of parasitoids in a risk-adjusting way, i.e. although more foragers were recruited to larger food items, attacking phorids reduced ant foraging activity by the same factor regardless of the size of the food offered. 7. The data suggest that S. richteri colonies juggle the needs to harvest food efficiently, reduce competition, and avoid excess risks from parasitoids in complex ways.     

昆明红火蚁种群发生特征

【目的】2013年10月云南省元谋县首次发现红火蚁。掌握红火蚁蚁巢各品级发生动态,能为当地红火蚁的防控提供技术支撑。【方法】2015年1—12月,在昆明宜良县对红火蚁蚁巢取样、分离,红火蚁取样、称重,统计红火蚁各品级的头数。【结果】地上蚁巢红火蚁蚁群数量发生高峰期在8—9月,其次是3—4月。蚁后数量比例高峰在3—4月;有翅雌蚁比例高峰在4月,其次是7月;有翅雄蚁比例高峰的在5月,其次是9月;生殖蚁幼虫和蛹比例高峰的3、4和12月。地上蚁巢工蚁、兵蚁、职能蚁幼虫和蛹数量发生的高峰期在8—9月,发生小高峰期在4月。【结论】昆明红火蚁蚁群数量动态有2个峰值,第一个峰值为8—9月,以职能蚁防治为主;第二个蜂值3—4月,以生殖蚁和职能蚁防治为主。该结果为昆明红火蚁防控技术提供了数据支撑。     

Interspecific competition between the red imported fire ant,Solenopsis invicta Buren and ghost ant,Tapinoma melanocephalum Fabricius for honeydew resources produced by an invasive mealybug,Phenacoccus solenopsis Tinsiley

In natural as in agricultural ecosystems, interactions between ants and honeydew-producing hemipterans are commonly observed. Mutualisms between invasive ants and hemipterans have been extensively studied in recent years. However, native ant species can equally exploit the honeydew excreted by hemipterans, and establish close relationships with them. Up till present, little is known about the competition between exotic ants (such as Solenopsis invicta) and its co-occurring species (e.g., Tapinoma melanocephalum) for this food resource. In this study, we compared the competitive ability of the invasive ant S. invicta and its co-occurring species T. melanocephalum in the laboratory. We also determined whether the two ant species could coexist and share honeydew resource. Our results indicate that the foraging activity of T. melanocephalum was restrained by S. invicta. Mortality of S. invicta and T. melanocephalum was significantly higher in T. melanocephalum colony case than that in other cases. The invasive ability between the two ant species was significantly different. These results suggest that S. invicta suppresses exploitation of honeydew-producing hemipterans by native ants and occupies most of honeydew resource. S. invicta could not completely drive T. melanocephalum out of honeydew competition, with small numbers of T. melanocephalum workers coexisting and sharing the honeydew with S. invicta. This finding permits a better understanding of the invasion success of S. invicta, and its ability to occupy new habitats.     

Exploitation of a high genomic mutation rate in Solenopsis invicta virus 1 to infer demographic information about its host, Solenopsis invicta

The RNA-dependent RNA polymerase (RdRp) region of Solenopsis invicta virus 1 (SINV-1) was sequenced from 47 infected colonies of S. invicta, S. richteri, S. geminata, and S. invicta/richteri hybrids collected from across the USA, northern Argentina, and northern Taiwan in an attempt to infer demographic information about the recent S. invicta introduction into Taiwan by phylogenetic analysis. Nucleotide sequences were calculated to exhibit an overall identity of >90% between geographically-separated samples. A total of 171 nucleotide variable sites (representing 22.4% of the region amplified) were mapped across the SINV-1 RdRp alignment and no insertions or deletions were detected. Phylogenetic analysis at the nucleotide level revealed clustering of Argentinean sequences, distinct from the USA sequences. Moreover, the SINV-1 RdRp sequences derived from recently introduced populations of S. invicta from northern Taiwan resided within the multiple USA groupings implicating the USA as the source for the recent introduction of S. invicta into Taiwan. Examination of the amino acid alignment for the RdRp revealed sequence identity >98% with only nine amino acid changes observed. Seven of these changes occurred in less than 4.3% of samples, while 2 (at positions 1266 and 1285) were featured prominently. Changes at positions 1266 and 1285 accounted for 36.2% and 34.0% of the samples, respectively. Two distinct groups were observed based on the amino acid residue at position 1266, Threonine or Serine. In cases where this amino acid was a Threonine, 90% of these sequences possessed a corresponding Valine at position 1285; only 10% of the Threonine¹²⁶⁶-containing sequences possessed an Isoleucine at the 1285 position. Among the Serine¹²⁶⁶ group, 76% possessed an Isoleucine at position 1285, while only 24% possessed a Valine. Thus, it appears that the Threonine¹²⁶⁶/Valine¹²⁸⁵ and Serine¹²⁶⁶/Isoleucine¹²⁸⁵ combinations are predominant phenotypes.     

Bacterial Diversity in <Emphasis Type="Italic">Solenopsis invicta</Emphasis> and <Emphasis Type="Italic">Solenopsis geminata</Emphasis> Ant Colonies Characterized by 16S amplicon 454 Pyrosequencing

Social insects harbor diverse assemblages of bacterial microbes, which may play a crucial role in the success or failure of biological invasions. The invasive fire ant Solenopsis invicta (Formicidae, Hymenoptera) is a model system for understanding the dynamics of invasive social insects and their biological control. However, little is known about microbes as biotic factors influencing the success or failure of ant invasions. This pilot study is the first attempt to characterize and compare microbial communities associated with the introduced S. invicta and the native Solenopsis geminata in the USA. Using 16S amplicon 454 pyrosequencing, bacterial communities of workers, brood, and soil from nest walls were compared between neighboring S. invicta and S. geminata colonies at Brackenridge Field Laboratory, Austin, Texas, with the aim of identifying potential pathogenic, commensal, or mutualistic microbial associates. Two samples of S. geminata workers showed high counts of Spiroplasma bacteria, a known pathogen or mutualist of other insects. A subsequent analysis using PCR and sequencing confirmed the presence of Spiroplasma in additional colonies of both Solenopsis species. Wolbachia was found in one alate sample of S. geminata, while one brood sample of S. invicta had a high count of Lactococcus. As expected, ant samples from both species showed much lower microbial diversity than the surrounding soil. Both ant species had similar overall bacterial diversities, although little overlap in specific microbes. To properly characterize a single bacterial community associated with a Solenopsis ant sample, rarefaction analyses indicate that it is necessary to obtain 5,000–10,000 sequences. Overall, 16S amplicon 454 pyrosequencing appears to be a cost-effective approach to screen whole microbial diversity associated with invasive ant species.     

Apparent facilitation of an invasive mealybug by an invasive ant

Summary In the southeast United States, the invasive ant Solenopsis invicta is known to derive important carbohydrate (honeydew) resources from mealybugs utilizing grasses. Most important appears to be an invasive mealybug, Antonina graminis. We studied whether this mealybug and a similar native species also benefit from association with S. invicta. We found that mealybug occurrence increases significantly with increasing proximity to S. invicta mounds, suggesting that mealybugs benefit as well. Mutual benefits derived by S. invicta and A. graminis are consistent with a hypothesis proposing that associations among invasive species can be important in their success at introduced locations.     

我国大陆红火蚁不同等级和虫态过冷却点的测定

了解我国红火蚁Solenopsis invicta Buren的耐低温能力并为其风险分析提供科学依据,本文对采自我国4个地点红火蚁蚁群中不同等级和虫态的过冷却点,以及不同季节和室内不同饥饿程度的工蚁过冷却点进行了测定。结果表明：蚁群中不同等级和虫态的过冷却点差异显著。工蚁成虫的过冷却点（－11.8±0.4℃）显著低于有翅雌蚁（－8.1±0.6℃）及蚁后（－7.9±0.5℃）,工蚁蛹和幼虫的过冷却点分别为－13.6±0.3℃和－12.1±0.4℃,蚁后蛹和幼虫的分别为－13.3±0.3℃和－12.2±0.3℃。工蚁蛹的过冷却点均显著低于其成虫和幼虫。蚁后蛹与其幼虫的过冷却点没有显著差异,但与其成虫的差异显著。同一未成熟期不同等级之间的也没有显著差异;不同季节的工蚁过冷却点有显著差异,其中以春季的最高（－4.3±0.2℃）,夏季（－6.6±0.2℃）、秋季（－9.4±0.1℃）的次之,冬季的（－12.0±0.3℃）最低;深圳、珠海、广州和陆川4个地理种群的工蚁过冷却点在春、秋和冬季无显著差异,但夏季陆川种群的过冷却点显著低于其他3个种群的（P<0.05）。饥饿可使工蚁的过冷却点明显升高,但大工蚁的过冷却点较小工蚁升高的幅度更大,饥饿15 d后的大工蚁比饥饿前的过冷却点升高了7.0℃,而小工蚁仅升高了4.9℃。这些结果为评价红火蚁在我国潜在的传播风险提供了理论依据。