Location: Imported Fire Ant and Household Insects Research
2025 Annual Report
Objectives
1. Characterize and develop an understanding of pathogenesis of Solenopsis invicta-specific viruses (e.g., Cripavirus porteri and Invictavirus solenopsae), microsporidia and other pathogenic microbes, and evaluate their impact as natural control agents against fire ants, the electric ant and tawny crazy ants.
Sub-objective 1.A: Develop natural enemies of fire ants as classical biological control agents or biopesticides by effecting their release, evaluating effectiveness, determining host specificity, and investigating pathogenesis.
Sub-objective 1.B: Characterize the prevalence and genetic diversity of the microsporidium Kneallhazia solenopsae among fire ant populations in both their native and invasive range. (MSA)
Sub-objective 1.C.: Describe microbial diversity in nests (both ants and soil) of the red imported fire ant, Solenopsis invicta, and soil not associated with their nests.
2. Develop new or improved low-cost control strategies (biodegradable and/or target specific) for sustained suppression of fire ants and other targeted invasive ant species, e.g., electric ant and tawny crazy ant, using a) biogenic amines/derivatives, and b) Receptor-i technology to discover strong binding peptide ligands to functionally interfere with critical G-Protein-Coupled-Receptors (GPCRs).
3. Conduct studies on the ecology and biology of tawny crazy ants to determine seasonal queen development and vulnerability in the field to optimize implementation of control technologies and strategies.
4. Develop new and improved surveillance/identification strategies for fire ants and other invasive ants using DNA metabarcoding, novel biochemical, and remote detection/identification methodologies to aid APHIS in fire ant quarantine efforts and facilitate ports-of-entry interceptions.
Sub-objective 4.A: Develop a universal DNA metabarcoding protocol that can be used to identify any non-native ant.
Sub-objective 4.B: Improve Remote Autonomous Detection System (RADS) identification of fire ants.
Sub-Objective 4.C: Develop with collaborator a RADS mobile application and device for real-time point-and-identify fire ant and other pest ants at plant nurseries and elsewhere.
5. Develop models to understand the role of genetics in fire ant adaptation to climate change to better predict future geographic distributions of fire ants and facilitate quarantine and early mitigation responses.
Sub-objective 5.A: Assess geographic genetic differentiation and selection processes among populations of Solenopsis invicta in both the native and invasive ranges.
Sub-objective 5.B: Develop predictive models of fire ant distribution in both the native and invasive range using climatic and genetic data.
Approach
Imported Fire Ants (IFA) and other invasive ants create significant problems worldwide. IFA thrive in disturbed habitats and humans are specialists at habitat disruption. About 90 years after IFA infested Mobile, Alabama they now occupy over 148 million hectares costing Americans more than eight billion dollars annually for control and damage repair. IFA impact many economic sectors, including households, electric and communications, and agriculture. About 10% of the human population is susceptible to developing allergic reactions to fire ant venom. Fire ants were introduced into the U.S. with few natural enemies. Thus, a major goal of the IFAHI unit is to increase the number of self-sustaining parasites and pathogens to improve IPM approaches against IFA and other invasive ants. The effectiveness of viruses and other pathogens will be investigated as control agents against fire ants in the laboratory and field. A readily adaptable Receptor-interference technology yields species-specific peptides that interfere with essential IFA functions resulting in worker and queen mortality. The method is readily adaptable to other invasive ants and pests. The unit will develop cutting-edge novel DNA based identification methods that will, with high accuracy, distinguish any invasive ant, facilitating early response and mitigation of incursions. Another system will remotely lure a target ant species into a tiny photo studio where the artificial intelligence-trained system will identify the ant and send data to APHIS or others. In addition, other invasive ant species, e.g., the tawny crazy ant will benefit from the innovations highlighted for IFAs but will need specific approaches for improved baits and baiting strategies, discovery of biological control agents, and improvement of IPM methods. The unit’s efforts will improve the near- and long-term suppression of invasive ant populations and benefit the broad range of stakeholders (e.g., livestock, nursery, households) impacted by IFA and other pest ants.
Progress Report
Under Objective 1, progress was made toward characterizing and developing an understanding of pathogenesis of Solenopsis invicta-specific viruses as natural control agents against fire ants. Suitable field sites were selected and permits obtained to conduct field releases of Solenopsis invicta virus 3 (Invictavirus solenopsae). Also, investigations have been begun to identify the protein receptor that mediates Solenopsis invicta virus 1 pathogenesis and entry into Solenopsis invicta cells. A newly discovered virus, Cripavirus porteri, is being characterized to determine its suitability as a natural control agent against the fire ant.
Primers were developed that target six loci of the pathogen of fire ants, Kneallhazia. solenopsae, including a ribonucleoprotein, an integral membrane protein, Periodic tryptophan protein, ABC transporter-like protein, ARF-guanine nucleotide exchange factor and Heat-shock-protein70. All six primers worked on K. solenopsae detected in black imported fire ants, S. richteri. No infection of K. solenopsae was detected in hybrid populations.
ARS scientists in Gainesville, Florida, in collaboration with researchers from the University of Florida, isolated 400 bacteria strains including 270 strains from ants, and 114 strains from the soil of six nests at two sites in Florida using four different selective media, including: nutrient agar, Luria-Bertani (LB) agar, tryptic soy agar, and chitin agar.
Under Objective 2, research on how newly mated fire ant queens quickly overcome the dealation inhibitory effects imposed on them by queen pheromones led to the discovery that tyramides were converted to the biogenic amine tyramine. Unexpectedly, tyramine fed to fire ant colonies resulted in worker and queen mortality. As promising as this appeared, field fire ants would not ingest tyramine dissolved in sucrose solution. An NSF SBIR phase 1 grant allowed us to investigate methods to overcome the distastefulness. Success was achieved using taste masking technology. Laboratory studies with field collected fire ant colonies showed the effectiveness of the formulation. A field trial is on-going. Both the active ingredient and the masking agent are cost effective and could lead to the first new fire ant control product in over 25 years.
ARS scientists in Gainesville, Florida and Corvalis, Oregon used their patented Receptor-interference technology to specifically isolate peptides that strongly bind to and inactivate fire ant PBAN G-Protein-Coupled-Receptors (GPCRs). Selected strong binding peptides fed to fire ant field colonies under laboratory conditions resulted in high worker mortality and death or sterilization of the queen. This was followed with very important colony mortality experiments in the field, where there are many more variables acting on the baits and resident ant colonies. Initial results show a reduction in treated fire ant colonies. Receptor-i technology has broad scope regarding peptides and the target pest insect. The peptides readily decompose in the environment and are specific to the target insect, thus little to no collateral damage is expected with these novel active ingredients. This research can be especially beneficial to organic nurseries, organic livestock producers (e.g., calving operations), and eco-conscious homeowners.
Significant progress was made on a subordinate project of ARS scientists in Gainesville, Florida through an interagency agreement with APHIS, and with scientists at Tennessee State University in McMinnville, Tennessee to develop method(s) to improve fire ant suppression in the nursery industry. The application of a surface spray of insecticide that is not repellent to fire ants, was compared with more traditional treatments of drenching root balls with repellent insecticides to disinfest fire ant colonies from trees harvested and shipped with large root balls (24-inch diameter, 340+ lbs.). Live fire ants were not detected in any of the ten root balls treated with the surface spray of the non-repellent insecticide (dinotefuran). In contrast, drench applications with the repellent insecticides bifenthrin, lambda cyhalothrin, and chlorpyrifos, and the water control remained infested in 30, 50, 80, and 50% of ten root balls each, respectively. In addition, 74% less insecticide solution was applied with the surface spray than with the drench application. This research addresses a concern for the Federal Imported Fire Ant Quarantine where approved treatments of nursery stock with large root balls for shipment outside of the quarantine can have inconsistent efficacy and are difficult for growers to apply.
Under Objective 3, to improve control strategies to stem the development of overwhelming populations of tawny crazy ants (TCA) in landscapes and structures, we hypothesized that a seasonal vulnerability of TCA occurs when queen larvae are developing. Providing ant baits that target queen larvae before they develop into numerous egg-producing queens could be an efficient way to prevent the development of large TCA populations. Two TCA infested field plots were established by installing nest boxes that facilitate TCA colony collection. Sampling through the winter and early summer (Nov. 2024 – June 2025) has thus far resulted in the collections of high numbers of adult queens but not any queen pupae which would indicate when larvae were present. Monthly sampling is continuing.
Under Objective 4, ARS scientists in Gainesville, Florida, in collaboration with researchers from the ARS-OBCL-Foundation for the Study of Invasive Species (FuEDEI) from Argentina, conducted a sampling of ants in Florida with the goal of describing the genetic diversity of nonnative ants. To do that they collected and morphologically identified 81 ants, 10 ants belong to 3 native species in Florida, while 71 ants were identified as 14 other ant species not native to Florida. These numbers exclude any Solenopsis invicta or S. geminata, as they are common non-native ants in Florida. DNA was extracted from each specimen and two sets of primers that target regions of the most common barcode for insects, the mitochondrial cytochrome c oxidase subunit I gene (mtDNA COX1) were successfully amplified.
To improve Remote Autonomous Detection System (RADS) identification of fire ants, an effective commercially available sticky trap was empirically found and incorporated into the trap module. The fire ant alarm pheromone activates fire ant workers and attracts them to the source. It was identified as a specific tri-substituted pyrazine. The compound is commercially available with a non-interfering isomer. The pyrazine is very volatile and was dissolved in mineral oil to retard its loss. RADs has a high-resolution camera and local Wi-Fi allows images to be sent to user database(s). Tens of thousands of images of fire ants and other co-habiting ant species were uploaded and used to train RADs to accurately identify red imported fire ants (accuracy is >94%).
The above research reflects progress toward meeting the goal to improve the near and long-term suppression of fire ants and other invasive pest ants. This will benefit a broad range of stakeholders and customers that include livestock and crop producers, commercial nurseries, the structural pest control industry, land managers of urban and natural landscapes, regulatory agencies, and homeowners.
Accomplishments
1. New fire ant venoms identified. ARS researchers at Gainesville, Florida believe the red imported fire ant (RIFA) and the black imported fire ant (BIFA) were inadvertently introduced into the United States over 90 years ago and currently infests about 300 million acres. It causes economic losses that exceed 8 billion dollars annually in the United States. While developing the InvictDetect Plus ImmunoStrip, a rapid field method to identify these ants for the Federal Imported Fire Ant Quarantine, unique venom proteins were discovered from RIFA, Solenopsis invicta. Data suggest that gene mixing between two introduced fire ant species has occurred earlier in the invasion than previously thought. Genotypic variation was discovered in the Solenopsis invicta venom 2 gene in a small number of RIFA, field colonies. Most of these unique genotypes exhibited strong identity to the Solenopsis richteri venom 2 gene (ortholog) from BIFA, Solenopsis richteri. Phylogenetic analysis of these sequences revealed a significant evolutionary relationship with the BIFA despite being identified as RIFA. A unique venom protein was also discovered in these colonies. Originating from a unique location on chromosome 10 where multiple duplication events have occurred, this resulted in the copying of this gene. Protein analyses have confirmed the presence of this venom protein. The results will impact the ability to accurately identify RIFA and BIFA which may influence the effectiveness of surveillance of these invasive species by regulatory agencies charged with containing the spread of fire ants, an invasive agricultural and public health pest.
2. Non-target ants feed on fire ant baits. ARS researchers at Gainesville, Florida believe fire ants are an invasive species which can be efficiently controlled with fire ant bait. However, after fire ants are controlled, new fire ants will reinfest-bait treated areas. One strategy to delay or prevent reinfestations is to conserve other ant species that can outcompete reinfesting fire ants. To facilitate the use of this strategy, eight commercial fire ant baits were presented to ten nontarget ant species in Florida and California to determine if any of the baits will not be fed upon by the nontarget ants. In both states, none of the baits tested were not fed upon by all non-target ant species. However, some baits were minimally fed upon by certain species. To help conserve nontarget ants, one should determine which nontarget ants are present at individual sites and whether these species forage upon and are adversely affected by the specific bait(s) being utilized. Incorporating the conservation of nontarget ants to slow the reinfestation by fire ants can benefit managers of natural and recreation lands such as parks and golf courses.
3. Finding better microsporidian strains to control invasive fire ants. ARS researchers at Gainesville, Florida suggest the red imported fire ant was accidentally introduced to the southern United States in the late 1930s from South America. A natural enemy of this invasive ant is the fungal-like microsporidian pathogen, Kneallhazia solenopsae, that is found in native populations of this ant. ARS scientists in Gainesville, Florida, in collaboration with researchers from the ARS-Overseas Biological Control Laboratories-Foundation for the Study of Invasive Species (FuEDEI) in Argentina described the presence of three different genotypes of this pathogen among three localities in Argentina. However, among four states in the US, only one genotype was found, and it was different from the genotypes in Argentina. This finding opens the possibility of evaluating the pathogenicity of these native microsporidian variants against fire ants in the US. This research may reveal variants with traits that improve fire ant control especially in areas where hybrid fire ants are extending their northern range. Establishing better variants would benefit nursery growers and other producers that must ship fire ant-free commodities beyond the fire ant quarantine.
Review Publications
Ascunce, M.S., Calcaterra, L.A., Shoemaker, D. 2025. Prevalence of a microsporidian parasite in different social forms of the Red Imported Fire Ant, Solenopsis invicta, in its native range in Argentina. Journal of Invertebrate Pathology. 210(108288). https://doi.org/10.1016/j.jip.2025.108288.
Ketehouli, T., Goss, E., Ascunce, M.S., Martins, S.J. 2024. Metabolic and physiological effects of antibiotic-induced dysbiosis in citrus. Ecotoxicology and Environmental Safety. 287:117325. https://doi.org/10.1016/j.ecoenv.2024.117325.
Oi, D.H., Atchison, R.A., Read, Q.D. 2024. Effect of fast and slow-acting bait toxicants on tawny crazy ant (Hymenoptera: Formicidae) foraging and nesting in the field. Journal of Economic Entomology. 118(1):329-338. https://doi.org/10.1093/jee/toae284.
Oi, D.H., Atchison, R.A., Henke, J.A. 2025. Acceptance of fire ant baits by nontarget ants in Florida and California. Florida Entomologist. 108(1):20240076. https://doi.org/10.1515/flaent-2024-0076.
Valles, S.M., Vander Meer, R.K., Estep Iii, A.S. 2025. Lateral flow immunoassay-based survey reveals a low frequency truncated Solenopsis invicta venom 2-like protein and unique Solenopsis invicta venom 2 protein genotypes in Solenopsis invicta. Frontiers in Insect Science. 5(1527130). https://doi.org/10.3389/finsc.2025.1527130.
Oliver, J.B., Addesso, K.M., Valles, S.M., Archer, R.S., Youssef, N.N., Pandey, M., Alexander, L.W., Weeks, R. 2025. Solenopsis invicta viruses and Kneallhazia solenopsae in Tennessee imported fire ant (Hymenoptera: Formicidae) Populations. Environmental Entomology. 54(3):553-564. https://doi.org/10.1093/ee/nvaf027.
Weldon, P.J., Vander Meer, R.K. 2025. Snake scent gland secretions repel and induce contact toxicosis in ants. Naturwissenschaften. 112(41). https://doi.org/10.1007/s00114-025-01990-4.
Morris, A., Vander Meer, R.K., Pereira, R., Chinta, S.P., Baldwin, R. 2025. The effect of fire ant (Hymenoptera: Formicidae) venom on ecologically relevant bacteria. Journal of Economic Entomology. toaf127. https://doi.org/10.1093/jee/toaf127.