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In the United States, imported fire ants are commonly referred to as red imported fire ants (Solenopsis invicta Buren), black imported fire ants (S. richteri Forel), and hybrid imported fire ants (S. invicta × S. richteri). They are significant pests, and their control heavily relies on synthetic insecticides. The extensive use of insecticides has led to public concern about their potential negative effects on human health and the well-being of wildlife and the environment. As an alternative, plant-derived natural compounds, particularly essential oils (EOs) and their main constituents, show promise as safe and environmentally friendly products for controlling fire ants. Repellants are useful in managing fire ants, and plant-derived natural repellants may serve as a safer and more environmentally friendly option. This study investigates the repellency of EO-derived compounds carvacrol, thymol, and their acetates against imported fire ant workers. The results revealed that carvacrol, a GRAS compound (Generally Recognized As Safe), was the most potent repellent against S. invicta, S. richteri, and their hybrid, with minimum repellent effective doses (MREDs) of 0.98 µg/g, 7.80 µg/g, and 0.98 µg/g, respectively. Thymol also exhibited strong repellency, with MREDs of 31.25 µg/g, 31.25 µg/g, and 7.8 µg/g, respectively. Furthermore, thyme-red essential oil, characterized by a thymol chemotype containing 48.8% thymol and 5.1% carvacrol, was found to effectively repel the hybrid ants with an MRED of 15.6 µg/g. In contrast, thyme essential oil, characterized by a linalool chemotype lacking thymol and carvacrol, did not exhibit any repellent effect, even at the highest tested dose of 125 µg/g. This study provides the first evidence of the potent repellency of carvacrol and thymol against imported fire ant workers, indicating their potential as promising repellents for fire ant control.

The red imported fire ant, Solenopsis invicta Buren (Hymenoptera: Formicidae), originally is from South America and currently infests over 128 million ha in the US. Its presence has caused significant social, environmental, and economic impacts. Over the decades, chemical insecticides have controlled these pest ants successfully. However, this method is costly and unsustainable because red imported fire ant re-establishes colonies quickly after chemical application. Thus, it is important to develop additional strategies for managing the red imported fire ant in the US. Solenopsis invicta virus 3 is a positive-sense, single-stranded RNA virus specific for S. invicta that offers promise as a classical biological control agent or biopesticide for control of S. invicta. Surveys were conducted to determine the prevalence of Solenopsis invicta virus 3 in alates of S. invicta collected from 5 urban areas (Tallahassee, Pensacola, Jacksonville, Gainesville, and Panama City) and 5 adjacent rural areas (Quincy, Jay, Macclenny, Lake City, and Blountstown) of North Florida, USA, using the reverse transcription polymerase chain reaction technique. The prevalence of Solenopsis invicta virus 3 varied widely from city to city. No statistically significant differences in alate infection rate was found between urban and rural cities sampled. Areas in which no infections of Solenopsis invicta virus 3 were detected may be good candidates for the introduction of this virus as a biological control agent to help manage this pest locally.

The red imported fire ant (Solenopsis invicta) escaped its natural enemies when it was introduced into North America in the 1930s from South America. US efforts have focused on discovery of natural enemies, like viruses, to provide sustainable control of the ant. Nine new virus genomes were sequenced from the invasive fire ant Solenopsis invicta using metagenomic RNA sequencing. The virus genomes were verified by Sanger sequencing and random amplification of cDNA ends reactions. In addition to the nine new virus genomes, the previously described Solenopsis viruses were also detected, including Solenopsis invicta virus 1 (SINV-1), SINV-2, SINV-3, SINV-4, SINV-5, and Solenopsis invicta densovirus. The virus sequences came from S. invicta workers, larvae, pupae, and dead workers taken from midden piles collected from across the ant’s native range in Formosa, Argentina. One of the new virus genomes (Solenopsis invicta virus 6) was also detected in populations of North American S. invicta. Phylogenetic analysis of the RNA dependent RNA polymerase, the entire nonstructural polyprotein, and genome characteristics were used to tentatively taxonomically place these new virus genome sequences; these include four new species of Dicistroviridae, one Polycipiviridae, one Iflaviridae, one Totiviridae, and two genome sequences that were too taxonomically divergent to be placed with certainty. The S. invicta virome is the best characterized from any ant species and includes 13 positive-sense, single-stranded RNA viruses (Solenopsis invicta virus 1 to Solenopsis invicta virus 13), one double-stranded RNA virus (Solenopsis midden virus), and one double-stranded DNA virus (Solenopsis invicta densovirus). These new additions to the S. invicta virome offer potentially new classical biological control agents for S. invicta.

As one of the most destructive and aggressive exotic harmful species, Solenopsis invicta Buren has spread rapidly in China, posing serious threats to biodiversity as well as human production and life. To formulate effective prevention and control measures, we first compared the bioclimatic variables of S. invicta between China and the USA. Subsequently, we employed the MaxEnt model and the “ecospat” package to predict the potential distribution and niche shift of S. invicta . The similar average annual temperature and annual precipitation between China and the USA serve as crucial ecological and environmental foundations for the successful invasion of S. invicta . Under the current climate, S. invicta is primarily distributed in the eastern and southern coastal regions of China and the USA. Under future climate scenarios, the suitable habitat area for S. invicta is projected to continue increasing in China, while it is expected to decrease in the USA. Mean diurnal range (Bio2), precipitation seasonality (Bio15), and other climatic factors exhibited vital‌ niche differentiation. The niche of S. invicta has significant shifted in both climatic and geographic spaces, while maintaining niche conservatism during the invasion process. S. invicta can effectively adapt to new habitats through niche shifts during the invasion process. It is not advisable to directly apply the prediction experiences and threshold values from the United States to guide the prevention and control of S. invicta in China in the future. Overall, the analysis provided a scientific basis for the government and local organizations to prevent and control S. invicta .

The red imported fire ant, Solenopsis invicta Buren (Hymenoptera: Formicidae), is a stinging, invasive ant from South America that has plagued the southern US since the 1930s. It is currently established in parts of California, including the Coachella Valley. We introduced and established the fire ant decapitating phorid flies, Pseudacteon curvatus Borgmeier and Pseudacteon obtusus Borgmeier (Diptera: Phoridae); Solenopsis invicta virus 3 (Picornavirales: Solinviviridae) (SINV-3); and the microsporidian fire ant pathogen Kneallhazia solenopsae Knell, Allan, & Hazard (Microsporida: Thelohaniidae) for the biological control of fire ants in this region of California. This is the first establishment of fire ant decapitating phorid flies in California. In addition, we demonstrated human-mediated establishment of SINV-3 and K. solenopsae in hot, dry, but irrigated, urban desert habitat.

In ants, dispersal strategies and morphology of female sexuals are generally linked to the mode of colony founding. In species using long-range dispersal tactics, queen/worker dimorphism is generally high and young queens are able to initiate new colonies by themselves, using their metabolic reserves. By contrast, in species using short-range dispersal strategies, queen/worker dimorphism is generally low and, due to their limited metabolic reserves, queens have lost the capacity to raise their brood alone and to found their colony independently. Moreover, polygyny is also often associated with short-range dispersal strategies, although the relationship between the number of queens and the dispersal strategy in ants is not clear-cut. Here, dispersal strategies were investigated in C. pygmaea, a highly polygynous and polydomous ant species from northeastern Brazil. Field observations and laboratory experiments show that this ant exhibits a suite of traits that are more commonly associated with long-range dispersal and independent colony foundation: functional wings in both males and females, high queen/worker dimorphism, strong weight loss in mature queens, nuptial flights and, in the lab, ability of young queens to found new colonies in haplometrotic conditions. On the other hand, this species shows a high degree of polygyny with a strong seasonal component, and, at least under laboratory conditions, mature queens seem able to develop propagules if they are accompanied by at least 10 workers. These features strongly suggest that (1) some of the gynes do not engage in a long-range dispersal but become new queens in their mother colony and (2) that budding events are possible in this species. We therefore speculate that C. pygmaea has a dual dispersal strategy probably related to environmental conditions: some gynes engage in long-range dispersal followed by independent colony foundation at the beginning of rainy season, while others mate in the parental colony and are re-adopted leading to high polygyny. During the rainy season, budding events can lead to colony extension and increased polydomy. Polydomy is commonly thought to improve resource discovery and exploitation through decentralized foraging behavior, a significant advantage during the rainy season when food ressources (mainly floral/extrafloral nectaries and hemipteran honeydew) are more abundant and when colony needs for food supplies are highest.

The red imported fire ant Solenopsis invicta Buren (fire ant hereafter) is a global pest that inflicts billions of dollars in damages to the United States economy and poses a major threat on a global scale. Concerns with the broad-spectrum application of insecticides have facilitated the hunt for natural enemy-mediated controls. One of these, the virus Solenopsis invicta virus-3 (SINV-3 hereafter) is exceptionally virulent in laboratory settings. However, despite high mortality rates in the laboratory and documented widespread SINV-3 prevalence in the southern United States, the fire ant remains a major pest. To explore this paradox, we document the immune response elicited by the fire ant when infected with SINV-3. We sequence the fire ant transcriptome prior to and following infection with SINV-3, and identify and discuss in detail genes in immune response pathways differentially expressed following infection with SINV-3. This information provides insights into genes and pathways involved in the SINV-3 infection response in the fire ant and offers avenues to pursue, to suppress key immune response genes and force the fire ant to succumb to SINV-3 infection in the field.

Venom plays several important roles in the life of the fire ant, Solenopsis invicta Buren. Laboratory rearing significantly affected the toxin component of S. invicta. However, the molecular mechanism of the change of venomous components when kept in the laboratory is unclear. In this study, RNA sequencing technique (RNA-Seq) was performed to explore differentially expressed genes in the venom gland of S. invicta at 0, 10, and 60 days after laboratory rearing. The RNA-Seq results showed that the expression of a large number of genes changed. The DEGs were involved in multiple pathways, including proteolysis, serine-type endopeptidase, and allergen. Furthermore, RNA-Seq and qRT-PCR data revealed that the expression of some genes related to proteolysis and allergen significantly decreased. Thus, our data generated new data relating to toxin-component and the transcriptome dynamics in the venom gland of S. invicta during laboratory rearing.

The high surface area to volume ratio of terrestrial insects makes them highly susceptible to desiccation mainly through the cuticle. Cuticular permeability (CP) is usually the most important factor limiting water loss in terrestrial insects. Water loss rate, percentage of total body water (%TBW) content, CP, and desiccation tolerance were investigated in workers of four Solenopsis species in the southeastern USA. We hypothesized that tropical/subtropical ants (S. invicta and S. geminata) will have lower CP values and tolerate higher levels of desiccation than temperate ants (S. richteri and S. invicta × S. richteri). The %TBW content was similar among species. Solenopsis invicta had a 1.3-fold and 1.1-fold lower CP value than S. invicta × S. richteri and S. richteri, respectively. Solenopsis geminata had a 1.3-fold lower CP value than S. invicta × S. richteri, and a 1.2-fold lower CP value than S. richteri. The LT50 values (lethal time to kill 50% of the population) ranged from 1.5 h (small S. geminata) to 8.5 h (large S. invicta). Desiccation tolerance ranged between 36 and 50 %TBW lost at death and was not related to a species’ location of origin. This study is the first report of water relations of S. invicta × S. richteri. It demonstrates that desiccation stress differentially can affect the survival of different Solenopsis species and implies that environmental stress can affect the distribution of these species in the southeastern USA.

Mortality and virus titer were monitored in Solenopsis invicta colony fragments to examine the impact of diet sucrose supplementation. Mortality on d 21 reached a mean of 111.8 ± 22.0 worker ants in Solenopsis invicta virus 3-treated colonies without sugar supplementation, which was significantly greater (F = 10.0; df = 3,14; P < 0.0009) than the Solenopsis invicta virus 3-infected colonies with sugar supplementation (33.5 ± 5.8), Solenopsis invicta virus 3-uninfected colonies without sugar supplementation (17.3 ± 10.7), and Solenopsis invicta virus 3-un-infected colonies with sugar supplementation (6.7 ± 2.5).