Invicta Colonies Research Articles

Enhancement of tolerance against flonicamid in Solenopsis invicta (Hymenoptera: Formicidae) through overexpression of CYP6A14

Solenopsis invicta is a main issue in southern China and is causing significant damage to the local ecological environment. The extensive use of insecticides has resulted in the development of tolerance in S. invicta. In our study, ten S. invicta colonies from Sichuan Province exhibited varying degrees of tolerance against flonicamid, with LC50 values from 0.49 mg/L to 8.54 mg/L. The sensitivity of S. invicta to flonicamid significantly increased after treatment with the P450 enzyme inhibitor piperonyl butoxide (PBO). Additionally, the activity of P450 in S. invicta was significantly enhanced after being treated with flonicamid. Flonicamid induced the expression levels of CYP4aa1, CYP9e2, CYP4C1, and CYP6A14. The expression levels of these P450 genes were significantly higher in the tolerant colonies compared to the sensitive colonies, and the relative copy numbers of CYP6A14 in the tolerant colonies were 2.01–2.15 fold. RNAi feeding treatment effectively inhibited the expression of P450 genes, thereby reducing the tolerance of S. invicta against flonicamid. In addition, the overexpression of CYP6A14 in D. melanogaster resulted in reduced sensitivity to flonicamid. Our investigations revealed hydrophobic interactions between flonicamid and seven amino acid residues of CYP6A14, along with the formation of a hydrogen bond between Glu306 and flonicamid. Our findings suggest that flonicamid can effectively control S. invicta and P450 plays a pivotal role in the tolerance of S. invicta against flonicamid. The overexpression of CYP6A14 also increased tolerance to flonicamid.

Evaluating control methods for red imported fire ant and their effects on hibiscus mealybug in citrus

AbstractThe red imported fire ant (Solenopsis invicta) may disrupt biological control of hibiscus mealybug (Nipaecoccus viridis) in Florida citrus. Controlling S. invicta may therefore be necessary for effective management of hibiscus mealybug. We evaluated four different methods to control S. invicta (ground applications of insecticide, two different insecticidal ant baits and spot‐treating ant colonies with hot water) to determine how these different treatments affected ants tending to hibiscus mealybug colonies, natural enemy abundance within hibiscus mealybug colonies and hibiscus mealybug colony abundance. While all treatments reduced the number of S. invicta colonies in treated areas compared to an untreated control, only ground applications of insecticide and the two ant baits significantly reduced the abundance of S. invicta found tending hibiscus mealybug colonies. Additionally, significantly more Brachymyrmex obscurior ants were found tending mealybug colonies in plots treated with either of the two ant baits. There was no significant effect of treatment on the abundance of natural enemies in hibiscus mealybug colonies, but significantly fewer natural enemies were found in mealybug colonies tended by S. invicta, and significantly more natural enemies were found in mealybug colonies tended by B. obscurior. Ground applications of insecticide, the abamectin ant bait Clinch and hot water treatments all reduced the overall number of hibiscus mealybug colonies compared with control areas, while the S‐methoprene ant bait Extinguish did not. Our results suggest that reducing the number of S. invicta tending hibiscus mealybug colonies can lead to higher natural enemy abundance and lower hibiscus mealybug abundance. However, methods used to control S. invicta may have different impacts on ant species like B. obscurior, leading to different outcomes with natural enemies.

Characterization of Solenopsis invicta virus 4, a polycipivirus infecting the red imported fire ant Solenopsis invicta.

Solenopsis invicta virus 4 (SINV-4), a new polycipivirus, was characterized in the host in which it was discovered, Solenopsis invicta. SINV-4 was detected in the worker and larval stages of S. invicta, but not in pupae, male or female alates, or queens. The SINV-4 titer was highest in worker ants, with a mean of 1.14 × 107 ± 5.84 ×107 SINV-4 genome equivalents/ng RNA. Electron microscopic examination of negatively stained samples from particles purified from SINV-4-infected fire ant workers revealed isometric particles with a mean diameter of 47.3 ± 1.4 nm. The mean inter-colony SINV-4 infection rate among S. invicta worker ants was 45.8 ± 38.6 in Alachua County, Florida. In S. invicta collected in Argentina, SINV-4 was detected in 22% of 54 colonies surveyed from across the Formosa region. There did not appear to be any seasonality associated with the SINV-4 infection rate among S. invicta nests. SINV-4 was successfully transmitted to uninfected S. invicta colonies by feeding. Among three colonies of S. invicta inoculated with SINV-4, two retained the infection for up to 72 days. The replicative genome strand of SINV-4 was detected in 18% (n = 11) of SINV-4-infected S. invicta colonies. Among 33 ant species examined, the plus genome strand of SINV-4 was detected in undetermined species of Dorymyrmex and Pheidole, Cyphomyrmex rimosus, Monomorium pharaonis, Pheidole obscurithorax, Solenopsis geminata, Solenopsis richteri, Solenopsis xyloni, and Solenopsis invicta. However, the replicative (minus) genome strand was only detected in S. invicta. SINV-4 infection did not impact brood production or queen fecundity in S. invicta. The mean brood rating (63.3% ± 8.8) after 31 days for SINV-4-infected colonies was not statistically different from that of uninfected colonies (48.3 ± 25.5). At the end of the 31-day test period, mean egg production was not significantly different between SINV-4-infected S. invicta colonies (287.7 ± 45.2 eggs laid/24 hours) and uninfected control colonies (193.0 ± 43.6 eggs laid/24 hours).

Invasion and high-elevation acclimation of the red imported fire ant, Solenopsis invicta, in the southern Blue Ridge Escarpment region of North America.

The red imported fire ant (Solenopsis invicta) is a non-native invasive species that rapidly spread northward in the United States after its introduction from South America in the 1930s. Researchers predicted that the northward spread of this invasive ant would be limited by cold temperatures with increased latitude and greater elevation in the Blue Ridge Escarpment region of the United States. The presence of S. invicta at relatively high elevations north of their projected limits suggests greater cold tolerance than previously predicted; however, these populations might be ephemeral indications of strong dispersal abilities. In this study, we investigated potential physiological adaptations of S. invicta that would indicate acclimation to high elevation environments. We hypothesized that if S. invicta colonies can persist in colder climates than where they originated, we would find gradients in S. invicta worker cold tolerance along a montane elevational gradient. We also predicted that higher elevation S. invicta ants might incur greater physiological costs to persist in the colder climate, so we measured colony lipid content to assess health status. For comparison, we also collected physiological temperature tolerance data for the co-occurring dominant native woodland ant Aphaenogaster picea. We found that S. invicta occurring at higher elevations exhibited greater physiological tolerance for cold temperatures as compared to lower-elevation conspecifics-a cold tolerance pattern that paralleled of the native A. picea ants along the same gradient. Both S. invicta and A. picea similarly exhibited lower thermal tolerances for colder temperatures when moving up the elevational gradient, with A. picea consistently exhibiting a lower thermal tolerance overall. There was no change in S. invicta colony lipid content with elevation, suggesting that greater metabolic rates were not needed to sustain these ants at high elevations.

Effects of maximum residue limit of triflumezopyrim exposure on fitness of the red imported fire ant Solenopsis invicta.

The impact of exposure to free feeding concentrations of triflumezopyrim to the red imported fire ant, Solenopsis invicta, in maximum residue tolerances for 56 days was investigated to understand whether triflumezopyrim, a novel neonicotinoid, poses unacceptable risks to the environment. Our results demonstrated that neither 0.5 μg/ml nor 0.2 μg/ml triflumezopyrim have a significant impact on the growth of the S. invicta colony and their food consumption (sugar water and locusts) during the length of treatment. While both 0.5 μg/ml and 0.2 μg/ml triflumezopyrim improved the grasping ability of S. invicta, and 0.5 μg/ml not 0.2 μg/ml triflumezopyrim increased their rate of locomotion. In addition, although 0.5 μg/ml and 0.2 μg/ml triflumezopyrim increased their individual aggressiveness index, the probability of the survival of S. invicta was not impacted by triflumezopyrim treatments in aggressive group encounters. This study suggests that triflumezopyrim did not have a negative impact on the fitness of S. invicta at 0.5 μg/ml and 0.2 μg/ml exposures.

Increased investment in the defence of high-value offspring by a superorganism

Parental investment theory predicts that parents should adjust their investment in offspring defence according to offspring value (i.e. the probability they will contribute to the next generation). Although previous research has shown this offspring value prediction is generally supported in unitary organisms, the ‘superorganisms’ formed by advanced colonial organisms have rarely been tested, and never by direct manipulation of offspring value. As an important complement to correlational studies, such a test would help better illuminate the applicability of the parental investment theory to that higher level of biological organization, as well as provide insight into the depth of the superorganism analogy. Here I use colonies of the fire ant, Solenopsis invicta, in a manipulative experiment to test whether superorganisms behave as predicted by the parental investment theory and invest more in defence (deliver larger venom doses) when protecting higher-value offspring. In addition, to test a proposed mechanism for observed increases, I conducted an experiment to investigate whether S. invicta alarm pheromone modulates venom dose. I found that colonies delivered larger venom doses when defending nests containing higher-value (sexual) offspring than when defending worker-destined brood, but I found no venom dose increase as a result of additional alarm pheromone. The conformity of S. invicta colonies to the offspring value prediction of the parental investment theory supports the theory's applicability to their higher (superorganismal) level of animal organization. It furthermore underscores that the superorganism concept is deeper than simple anatomical/organizational analogy, but extends also to colony-level behaviour.

Prospecting for viral natural enemies of the fire ant Solenopsis invicta in Argentina.

Metagenomics and next generation sequencing were employed to discover new virus natural enemies of the fire ant, Solenopsis invicta Buren in its native range (i.e., Formosa, Argentina) with the ultimate goal of testing and releasing new viral pathogens into U.S. S. invicta populations to provide natural, sustainable control of this ant. RNA was purified from worker ants from 182 S. invicta colonies, which was pooled into 4 groups according to location. A library was created from each group and sequenced using Illumina Miseq technology. After a series of winnowing methods to remove S. invicta genes, known S. invicta virus genes, and all other non-virus gene sequences, 61,944 unique singletons were identified with virus identity. These were assembled de novo yielding 171 contiguous sequences with significant identity to non-plant virus genes. Fifteen contiguous sequences exhibited very high expression rates and were detected in all four gene libraries. One contig (Contig_29) exhibited the highest expression level overall and across all four gene libraries. Random amplification of cDNA ends analyses expanded this contiguous sequence yielding a complete virus genome, which we have provisionally named Solenopsis invicta virus 5 (SINV-5). SINV-5 is a positive-sense, single-stranded RNA virus with genome characteristics consistent with insect-infecting viruses from the family Dicistroviridae. Moreover, the replicative genome strand of SINV-5 was detected in worker ants indicating that S. invicta serves as host for the virus. Many additional sequences were identified that are likely of viral origin. These sequences await further investigation to determine their origins and relationship with S. invicta. This study expands knowledge of the RNA virome diversity found within S. invicta populations.

Toxicity and sublethal effects of sulfoxaflor on the red imported fire ant, Solenopsis invicta

To understand whether sulfoxaflor, a novel neonicotinoid, poses unacceptable risks to the environment, it is important to assess its effects on nontarget insects. Therefore, the effects of short-term exposure (28 days) of free-feeding sublethal concentrations (1–2μg/ml) of sulfoxaflor to the red imported fire ant, Solenopsis invicta, were investigated. The following parameters were evaluated to determine the impact of exposure: colony growth, food consumption (sugar water and locusts), and interspecific interactions. Sulfoxaflor exposure produced significant negative effects on S. invicta colony growth, with cumulative colony weight losses of 83.36% and 100.00% after treatment with 1μg/ml and 2μg/ml, respectively. The consumption of sugar water (containing sulfoxaflor) of surviving colonies decreased with increasing sulfoxaflor concentration. Moreover, the consumption of locusts decreased after treatment with 2μg/ml, but not 1μg/ml, sulfoxaflor. Sulfoxaflor treatment for 14 days led to reduced aggressiveness of S. invicta workers in interspecific confrontations (S. invicta vs. unexposed Pheidole fervida), and their probability of survival of aggressive encounters was reduced significantly to 48% of that of control ants. Our results indicate that sublethal concentrations of sulfoxaflor are likely to have a negative impact on ants.

From cryptic herbivore to predator: stable isotopes reveal consistent variability in trophic levels in an ant population.

Populations may collectively exhibit a broad diet because individuals have large diet breadths and/or because subpopulations of specialists co-occur. In social insect populations, the diet of the genetic individual, the colony, may similarly arise because workers are diet generalists or castes of specialists. We used elemental and isotopic methods to explore how the invasive red imported fire ant, Solenopsis invicta, achieves its status as a trophic generalist. In one 0.5-ha old field, 31 S.invicta colonies ranged from 1°-consumer to 2°-predator (δ15 N's 0.35-7.38‰), a range comparable to that shown in sampled ant communities. Moreover, a colony's trophic rank was stable despite δ15 N fluctuating 2.98‰ over the year. Colonies that fed at higher trophic levels were not larger, but consumed more C3 -based resources. Individual worker mass, however, did increase with δ15 N (r2 =0.29, P<0.001). The ninefold variation in worker mass within a colony generated trophic variance approximately 15% of the population of colonies. Combined, we show how intraspecific trait variation contributes to the trophic breadth of S.invicta, and suggest mechanisms that further explain how their trophic signature varies across space, but remains stable over time.

Manipulation of Viral Titers ofSolenopsis invictaVirus-1 by RNA Interference in Laboratory Colonies of Red Imported Fire Ant1

Abstract. The red imported fire ant, Solenopsis invicta Buren, native to South America, is an economically important urban pest that has few natural enemies in the southern United States. Solenopsis invicta virus-1 (SINV-1) is a picorna-like single-stranded positive-sense virus known to affect only S. invicta. RNA interference (RNAi) is a known regulator of RNA viruses in biological systems and is an emerging biologically based insect control method. The purpose of this study was to increase, then decrease viral titers of SINV-1 in S. invicta colonies during a period of 1 month to demonstrate a possible use of SINV-1 as a targeted, controllable management strategy against S. invicta. Manipulation of SINV-1 viral titers was attempted by first exposing S. invicta colonies to SINV-1 and after 15 days exposing the same colonies to novel double-stranded RNA (dsRNA) coded for SINV-1 viral capsid genes. S. invicta colonies were monitored during the 1-month period, and significant increases and decreases in viral...

Food competition mechanism between Solenopsis invicta Buren and Tapinoma melanocephalum Fabricius

This study compared the amount of food resource depletion and interference competition at the individual and colony levels between Solenopsis invicta and Tapinoma melanocephalum laboratory colonies. The consumption of sausage, honey water, and mealworm by S. invicta colonies of equal worker number was higher than that by T. melanocephalum colonies. The consumption of sausage and honey water by S. invicta colonies of equal worker number was significantly higher than that by T. melanocephalum colonies. However, the amounts of sausage, honey water, and mealworm depleted by S. invicta colonies of equal worker biomass were lower than those depleted by T. melanocephalum colonies. The consumption of sausage and mealworm by S. invicta colonies of equal worker biomass were also significantly lower than that by T. melanocephalum colonies. Individual-level interference competition between S. invicta and T. melanocephalum colonies in limited space was intense. Competition intensity and the death rate reached their maximum when the worker numbers of both colonies were equal. In any proportion, the death rate of T. melanocephalum reached over 80%, higher than that of S. invicta . S. invicta colonies of equal worker biomass and equal worker number recruited more workers for colony-level interference competition and used more resources. However, the death rates among S. invicta colonies were higher than those among T. melanocephalum colonies. The active resource plundering of S. invicta reflected their intense competitiveness and limited the range of activity of T. melanocephalum .

Solenopsis invicta virus 3: Pathogenesis and stage specificity in red imported fire ants

Solenopsis invicta colonies were exposed to purified preparations of Solenopsis invicta virus 3 (SINV-3) to investigate virus pathogenesis at the colony level. Time course experiments revealed an infection exhibiting specificity for the adult stage (workers). SINV-3 genome and a capsid protein were increasingly present in worker ants with time. Northern blot analysis revealed two bands in RNA preparations from worker ants infected with SINV-3 corresponding to the genomic and sub-genomic species. Conversely, larval RNA preparations from SINV-3-infected colonies showed a near-complete absence of SINV-3 genome or sub-genome. The data confirm that SINV-3 is the etiological agent causing mortality among S. invicta colonies in the laboratory. We propose that SINV-3 infection somehow alters worker ant behavior, which may prevent them from acquiring and/or distributing solid food to the larvae. Consequently, larval mortality and impaired queen health occur as a result of starvation or neglect by the worker caste.

The Role of Habitat in the Persistence of Fire Ant Populations

The association of the exotic fire ant, Solenopsis invicta with man-modified habitats has been amply demonstrated, but the fate of such populations if ecological succession proceeds has rarely been investigated. Resurvey of a fire ant population in a longleaf pine plantation after 25 years showed that the recovery of the site from habitat disturbance was associated with a large fire ant population decline. Most of the persisting colonies were associated with the disturbance caused by vehicle tracks. In a second study, mature monogyne fire ant colonies that had been planted in experimental plots in native groundcover of the north Florida longleaf pine forest had mostly vanished six years later. These observations and experiments show that S. invicta colonies rarely persist in the native habitat of these pine forests, probably because they are not replaced when they die. A single site harbored a modest population of polygyne fire ants whose persistence was probably facilitated by reproduction through colony fission.

Sampling Efficacy for the Red Imported Fire AntSolenopsis invicta(Hymenoptera: Formicidae)

Cost-effective detection of invasive ant colonies before establishment in new ranges is imperative for the protection of national borders and reducing their global impact. We examined the sampling efficiency of food-baits and pitfall traps (baited and nonbaited) in detecting isolated red imported fire ant (Solenopsis invicta Buren) nests in multiple environments in Gainesville, FL. Fire ants demonstrated a significantly higher preference for a mixed protein food type (hotdog or ground meat combined with sweet peanut butter) than for the sugar or water baits offered. Foraging distance success was a function of colony size, detection trap used, and surveillance duration. Colony gyne number did not influence detection success. Workers from small nests (0- to 15-cm mound diameter) traveled no >3 m to a food source, whereas large colonies (>30-cm mound diameter) traveled up to 17 m. Baited pitfall traps performed best at detecting incipient ant colonies followed by nonbaited pitfall traps then food baits, whereas food baits performed well when trying to detect large colonies. These results were used to create an interactive model in Microsoft Excel, whereby surveillance managers can alter trap type, density, and duration parameters to estimate the probability of detecting specified or unknown S. invicta colony sizes. This model will support decision makers who need to balance the sampling cost and risk of failure to detect fire ant colonies.

Delivery System using Sodium Alginate Virus Loaded Pellets to Red Imported Fire Ants (Solenopsis invicta, Hymenoptera: Formicidae)

ABSTRACT Microencapsulation as a delivery mechanism of SINV-1 and other molecules such as dsRNA, offers an approach to Solenopsis invicta Buren management that is target specific and fits current approaches to baiting ants with toxins and/or RNA-interference. The delivery method presented here targets ground dwelling, foraging ants with an ant-infecting virus which is specific to the genus, Solenopsis. Endemic ant-infecting viruses, like S. invicta viruses (SINV-1, SINV-2, and SINV-3) are being evaluated for efficacy in S. invicta population suppression. In this study, SINV-1 (TX5 strain) was extracted from S. invicta colonies and microencapsulated in sodium alginate pellets. Pellets containing extracted whole virions were offered to confirmed non-infected S. invicta colonies. Colonies were sampled every 5 d and tested by reverse transcription polymerase chain reaction (RT-PCR) for presence of viral RNA. The longevity of control and viral pellets were also evaluated. Within 30 d, post-feeding of virus, 35...

Bacterial Diversity in Solenopsis invicta and Solenopsis geminata 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.

Phorid Flies,Pseudacteonspp. (Diptera: Phoridae), Affect Forager Size Ratios of Red Imported Fire AntsSolenopsis invicta(Hymenoptera: Formicidae) in Texas

Multiple species of Pseudacteon phorid flies (Diptera: Phoridae) are currently being released throughout the southern United States to aid biological control of red imported fire ants, Solenopsis invicta Buren (Hymenoptera: Formicidae). It is anticipated that these flies will interfere with S. invicta foraging, allowing native ant assemblages to outcompete S. invicta for available resources. Numerous studies have shown a decrease in S. invicta foraging intensity when exposed to phorids. This study documents a behavioral change in phorid-exposed S. invicta colonies at a phorid release site in central Texas. Significant differences in forager size ratios were detected between phorid-exposed and phorid-absent colonies. A similar phenomenon was recently documented in the native range of these insects in South America as well. Experimental manipulation of ratios of S. invicta worker sizes has been shown to have important effects on colony success. This newly documented phorid-mediated S. invicta colony-level effect represents a significant shift in S. invicta foraging dynamics and may provide an additional mechanism by which phorids can influence S. invicta populations in their United States range.

A new fire ant (Hymenoptera: Formicidae) bait base carrier for moist conditions

A new water-resistant fire ant bait (T-bait; cypermethrin 0.128%) consisting of dried distillers grains with solubles (DDGS) as a carrier was developed and evaluated against a standard commercial bait (Advion; indoxacarb 0.045%) under both laboratory and field conditions. When applying the normal T-bait or Advion in the laboratory, 100% of Solenopsis invicta Buren worker ants were killed within 4 days. However, when the T-bait and Advion were wetted, 70.6 and 39.7% of the ants were killed respectively. Under field conditions, dry T-bait and dry Advion had almost the same efficacy against ant colonies. However, when T-bait and Advion came in contact with water, the former's ability to kill S. invicta colonies in the field was only marginally reduced, while Advion lost virtually all of its activity. In addition, DDGS was also shown to be compatible with a number of other insecticides, such as d-allethrin, permethrin and pyrethrin. Based on its properties of remaining attractive to the fire ants when wetted, combined with its ant-killing abilities both in the laboratory and in the field, T-bait is an efficient fire ant bait, especially under moist conditions.

Discovery and effects of Texas Solenopsis invicta virus [SINV-1 (TX5)] on red imported fire ant populations

Solenopsis invicta Buren (Hymenoptera: Formicidae), the red imported fire ant is native to South America but has invaded areas of the southeastern US, and parts of Southern California. The S. invicta virus-1 (SINV-1) is a positive sense, single-stranded RNA picorna-like virus that only affects Solenopsis species. The virus can infect all caste members and developmental stages. Infection of SINV-1 can result in colony collapse in less than 3 months under laboratory conditions. This study screened S. invicta colonies from Texas for the presence of SINV through Reverse Transcriptase PCR (RT-PCR). Positive samples were genetically characterized by direct sequencing and compared with known picorna-like viruses. SINV-1 was detected in ant colonies from Smith and Henderson TX counties. Amino acid sequence comparison of SINV-1 (TX5) ORF2 region showed homologies of 96% with SINV-1, 97% with SINV-1A, 17.6% with SINV-2, and 20.7% with SINV-3. In addition, SINV-1 (TX5) was compared to 18 other Dicistroviridae viruses. Ant-infecting viruses may provide new approaches to suppressing these important economic pests.

Laboratory host specificity testing of the fire ant microsporidian pathogen Vairimorpha invictae (Microsporidia: Burenellidae)

The host specificity of Vairimorpha invictae, a microsporidian pathogen of fire ants in South America, was assessed in the laboratory. Species evaluated included the tropical fire ant, Solenopsis geminata, the southern fire ant, Solenopsis xyloni, and the Argentine ant, Linepithema humile. The two fire ant species are native to North America. The Argentine ant is a widespread, exotic species that co-occurs with the native North American fire ants as well as with the red imported fire ant, Solenopsis invicta, and the black imported fire ant, Solenopsis richteri, in the US. Inoculations of V. invictae-infected S. invicta brood to laboratory colonies did not result in any infections of S. geminata, S. xyloni, or L. humile, while 60% of the S. invicta colonies developed infections. V. invictae was not detected in smaller groups of S. geminata and S. xyloni larvae that were tended by V. invictae-infected adult, S. invicta workers, but was detected in 40% of the S. invicta larval groups tended by infected workers. This was the first report of V. invictae transmission to larvae by infected adult worker ants. Exposure to V. invictae by contact with infected brood and workers partially emulated possible field interactions between infected and uninfected ant species. These results are congruent with previous field surveys which indicate that the host range of V. invictae is limited to fire ants of the Solenopsis saevissima species group.