Location: Imported Fire Ant and Household Insects Research
2015 Annual Report
Objectives
Objective 1: Develop advanced integrated pest management methods by improving the understanding of fire ant biology and by expanding biologically-based control of fire ants through detailed genetic, behavioral, physiological, chemical, and ecological studies of fire ants and their natural enemies.
a. Employ metagenomics techniques and biological control prospecting to discover additional natural enemies of introduced fire ants.
b. Characterize the genetic architecture of the Gp-9 supergene involved in regulation of fire ant colony social form.
c. Develop natural enemies of fire ants as classical biological control agents or biopesticides by evaluating their effectiveness, determining host specificity, developing methods for rearing and release, and formulating more effective biopesticides.
d. Develop novel biologically-based fire ant control by identifying the behavioral and semiochemical underpinnings of fire ant mating flights and colony establishment.
Objective 2: Develop advanced integrated pest management methods by improving the understanding of the biology of invasive pest ants other than fire ants and by expanding options for their management and surveillance.
a. Improve control of tawny crazy ants: 1) refine integrated management strategies; 2) evaluate natural enemies; and 3) determine whether crazy ant semiochemicals can be used to enhance baits and improve surveillance/detection methods.
b) Develop or improve control methods for other important invasive ants (e.g., Argentine ant, little fire ants) through evaluation and consolidation of current or new control methodologies.
c) Establish a collection database and repository for fire ants and other pest ants to facilitate discovery of natural enemies, genetic studies, and taxonomic identifications.
Objective 3: Determine impacts of climate and climate change on potential distributions of invasive ants.
Approach
1. a) Fire ants (Solenopsis invicta) from the native range will be collected and used as source material to create cDNA expression libraries. Detailed bioinformatics analysis of resulting sequence data will be screened to identify potential fungi, viruses, protists, and non-hymenopteran eukaryotic parasites. North American fire ant colonies will be exposed to fire ants collected from South America and observed for signs of pathology. These colonies will be examined using various molecular analyses and microscopic methods to determine the etiological agent. b) A linkage map will be developed to identify all of the genes in the Gp-9 non-recombining region. Linkage disequilibrium between the Gp-9 genes and social form will be estimated with several different statistical methods. Products and functions of the genes comprising the Gp-9 supergene will be inferred by bioinformatic analysis. c) Natural agents will be evaluated for their suitability as control agents against U.S. populations of the fire ant by establishing their host specificity, mode of dissemination (formulation), efficacy, virulence, mode of action, mass rearing, and field release. d) The role of semiochemicals in fire ant biology will be established and possibly exploited as a control agent by exposing colonies and/or individual ants to extracts or synthetic chemicals and recording behavioral changes.
2. a) Effective and alternative control methods will be investigated for the tawny crazy ant by treating infected areas with soil applied systemic insecticides or lures and evaluating for efficacy. The transcriptome of the tawny crazy ant will be sequenced and examined for the presence of potential natural enemies. Promising potential natural enemies, including the tawny crazy ant virus, will be tested to determine efficacy and safety. Seasonal phenology of tawny crazy ant colonies will be established to better direct control efforts by excavating nests monthly and quantifying different stages. b) For tawny crazy ants and other invasive pest ants, e.g. Argentine ant little fire ants, the contents of well-developed ant exocrine glands will be chemically identified and subjected to behavioral bioassays to determine the effect of pheromones on ingestion of baits, bait discovery, field efficacy evaluations, and the effective longevity of attractant/bait formulations. Where attractive pheromones have not been already identified, a Y-tube olfactometer bioassay will be used to isolate and identify active compounds. c) A pest ant database and repository will be assembled using existing electronic data and specimens from labs across the country. Maps for existing pest ant collections will be generated and used to guide future collection efforts as needed. Future specimens and collection data will be systematically incorporated into the repositories.
3. Climate matching protocols in Climex 3.0.2 (Hearne Software, Victoria, Australia) will be used to predict potential future ranges of 15 exotic pest ants. Distributional data will be categorized as rural and urban with extreme outliers noted and eliminated when appropriate (e.g., detection in green houses).
Progress Report
Objective 1a: 182 live fire ant colony samples were collected from across northern Argentina where S. invicta is purported to be native and returned to the United States where they were held in quarantine for further study. Eight gene libraries were created from these ant samples (grouped geographically and by stage) followed by next generation gene sequencing. The raw sequencing data were processed to subtract fire ant genes and then database searches were conducted on the remaining assembled sequences with the intention of identifying natural infections. The libraries have yielded large numbers of possible natural enemies that need to be investigated further to establish their relationship to the ant (pathogen or not) and whether they can be used as control agents for fire ants in the U.S. Initial prospecting for natural enemies was also conducted with a unique etiology-guided approach. The abundance and distribution of known pathogens were determined and transmission tests were conducted with a recently discovered fire ant densovirus. Objective 1b: Genome sequence data of numerous males was generated. Preliminary analyses suggest the Gp-9 supergene has remained intact across several ant species, with no evidence for recombination. A large-scale study has been initiated to investigate the possibility of segregation distortion. Such distortion is predicted as another selfish genetic trait of the supergene that favors its persistence in wild populations despite its detrimental effects on individual ants. Large embryo progenies of more than 120 queens have been collected and subsamples of 30-35 embryos per progeny currently are being genotyped. Behavioral studies also were initiated to determine whether the supergene also controls social organization in a distantly related fire ant. Objective 1c: Field release techniques were developed for the virus, Solenopsis invicta virus 3 (SINV-3) (including bait and drench formulations) and field releases were made in California and are planned for Puerto Rico where the virus is absent. The virus was successfully established in the locations where it was released (Florida and California). Also, the SINV-3 dose necessary to establish a lethal infection in laboratory colonies of fire ants was established. These data are necessary to successfully use the virus as a biopesticide and for releasing the virus as a classical biological control agent. Research on the potential use of Pseudacteon decapitating flies against invasive tropical fire ant populations in Hawaii, Guam, and other Pacific islands has progressed quickly over the last year. We have been able to collect and mass rear Pseudacteon bifidus flies from native tropical fire ant populations in Texas in cooperation with our colleagues in Texas. Last fall we completed host specificity studies, which showed that this species will not be a threat to any native ants found in the Pacific or Pacific Rim nations. This spring, we, and our cooperators were able to complete host suitability tests with tropical fire ants from Hawaii, Guam, and the Galapagos. Data from these tests will shortly be submitted to regulatory officials to determine if we can proceed with field releases of natural control agent. Objective 1d: The major chemical constituents of the male reproductive system were defined qualitatively and quantitated. Large amounts of free fatty acids (FFA) were found throughout the male reproductive system, as well as in the uninseminated female sexual reproductive system. These FFAs are known to have both insecticidal and strong antibiotic activity. The role these compounds play in reproduction and colony foundation/establishment is under further investigation. The role of other compounds specific to males has been investigated through a CRADA. Interference of the mating process or premature queen development by unmated females within colonies would minimally decrease the reproductive potential of fire ant populations and add to our integrated fire ant management tools. Under Objectives 2a and b, significant progress was made in identifying a bait that is effective against colonies of the tawny crazy ant. A liquid bait formulation was found to be readily consumed by these ants and caused significant laboratory colony mortality. Field tests demonstrated overnight suppression of tawny crazy ant activity, which was sustained, as long as bait was available . Progress was also made in documenting the seasonal phenology of tawny crazy ant queen reproduction. Monthly sampling of queens and ovary dissections revealed that mature eggs were present in ovaries throughout the year; however, fewer queens were collected during the winter. These data suggested that winter treatments may be an opportune time to eliminate queens before they proliferate in the spring and summer. Objective 2c: We assembled a core team from four institutions and established a general framework of how to catalogue and store our extensive collections of pest ants. More than 2,000 ant collections from the Fundación para el Estudio de Especies Invasivas (FuEDEI) in Argentina (mostly fire ants) have been organized and catalogued. We are currently preparing to compile this information with existing collection databases in Florida. We have begun testing a sophisticated online database for the joint use of core team members and another online database (AntWeb) for general publication and mapping of collection records. These efforts will facilitate discovery of natural enemies, genetic studies, taxonomic identifications, and be useful in Objective 3.
Accomplishments
1. Biocontrol agents released in southern California. Fire ant populations in the United States were introduced without some of their natural enemies and competitive ant species. As a result, they are a significant pest and continue to expand their range in the United States. Known fire ant pathogens and parasites were absent in southern California fire ant populations. ARS researchers, Gainesville, Florida, in collaboration with the Coachella Valley Mosquito and Vector Control District introduced Solenopsis invicta virus 3 (SINV-3), a microsporidian (Kneallhazia solenopsae) pathogen, and a phorid fly parasite of fire ants into the urbanized desert habitat of the Coachella Valley in southern California. SINV-3 has begun to spread throughout the population as has the Kneallhazia pathogen. In addition, fire ant decapitating flies in California have survived the extreme summer heat of the desert. Establishing a suite of fire ant natural enemies as biological control agents is a self-sustaining control strategy for the suppression of invasive fire ants. Further evaluations will determine the overall effect of fire ant parasites and pathogens on introduced fire ant populations in California.
2. Lethal dose of Solenopsis invicta virus 3 (SINV-3) established. SINV-3 is being developed as a biopesticide, an alternative to traditional insecticides. The dose required to initiate a lethal response in fire ants needed to be established empirically to advance its use as a biopesticide. ARS researchers at Gainesville, Florida, determined the dose required to cause lethality in fire ants and the minimum dose required to establish a long term infection. These experiments represent a necessary step to utilization of SINV-3 as a biopesticide and natural agent to control fire ants in the United States. Indeed, SINV-3 has been successfully released into fire ant populations in Florida and California.
3. Two viruses, SINV-1 and SINV-2, are associated with different fitness costs and gene expression patterns in fire ants. The dynamics of host-viral interactions and the fitness consequences of viruses in fire ant queens are poorly understood. ARS researchers in Gainesville, Florida demonstrated viral infection dynamics in fire ants are variable and respond to multiple internal and external factors in the host, including its behaviour, physiological state and social environment. Stress associated with queen colony founding and trade-offs between competition, immunity and reproduction clearly play key roles in regulating infection dynamics.
4. Tests of diets for growth of laboratory fire ant colonies. Healthy laboratory fire ant colonies are essential for many laboratory studies including the transmission, host specificity and impacts of potential biological control agents. USDA-ARS scientists in Gainesville, FL conducted a six-week test which compared fire ant colony growth rates with 13 different diets. Results showed that colonies grew best when fed domestic crickets, roaches, or mealworms. However, colony growth was poor with house flies, night crawlers, hamburger, or waxworms. The other diets produced intermediate results. This study is important because it will allow fire ant researchers in different regions to select effective diets and avoid diets not suitable for their laboratory tests.
Review Publications
Bjornson, S., Oi, D.H. 2014. Microsporidia Biological Control Agents and Pathogens of Beneficial Insects. In: Weiss, L.M., Becnel, J.J., editors. Microsporidia: Pathogens of Opportunity. First Edition. Chichester, UK: John Wiley & Sons, Inc. p.635-670. doi: 10.1002/9781118395264.ch25.
Meszaros, A., Oi, D.H., Valles, S.M., Beuzelin, J.M., Reay-Jones, F.P., Johnson, S.J. 2014. Pseudacteon spp. (Diptera: Phoridae) biological control agents of Solenopsis spp. (Hymenoptera: Formicidae) in Louisiana: statewide distribution and Kneallhazia solenopsae (Microsporidia: Thelohaniidae) prevalence. Biological Control. 77:93-100.
Plowes, R.M., Becnel, J.J., Lebrun, E.G., Oi, D.H., Valles, S.M., Jones, N.T., Gilbert, L.E. 2015. Myrmecomorba nylanderiae gen. et sp. nov., a microsporidian parasite of the Tawny Crazy Ant, Nylanderia fulva. Journal of Invertebrate Pathology. 129:45-56.
Porter, S.D., Valles, S.M., Oi, D.H. 2013. Host specificity and colony impacts of Solenopsis invicta virus 3. Journal of Invertebrate Pathology. 114:1-6.
Porter, S.D., Valles, S.M., Wild, A., Dieckmann, R., Plowes, N.J. 2015. Solenopsis invicta virus 3: Further host-specificity tests with native Solenopsis ants (Hymenoptera: Formicidae). Florida Entomologist. 98:122-125.
Graham, L.C., Porter, S.D., Bertagnolli, V.E. 2003. Phorid Flies in Alabama: A tale of two species. Journal of Agricultural and Urban Entomology. 20:165-171.
Resasco, J., Porter, S.D., Sanders, N.J., Levey, D.J. 2014. Testing sodium limitation of fire ants in the field and laboratory. Ecological Entomology. 39:267-271.
Barriga, P.A., Sloan, J.V., Porter, S.D., Sagers, C.L. 2013. Stable isotope enrichment in laboratory ant colonies: effects of colony age, metamorphosis, diet, and fat storage. Entomologia Experimentalis et Applicata. 149:265-272.
Resasco, J., Haddad, N.M., Orrock, J.L., Shoemaker, D.D., Brudvig, L.A., Damschen, E.I., Tewksbury, J.J., Levey, D.J. 2014. Landscape corridors can increase invasion by an exotic species and reduce diversity of native species. Ecology. 95:2033-2039.
Gotzek, D., Axen, H.J., Helms-Cahan, S., Shoemaker, D.D. 2014. Global Invasion History of the Tropical Fire Ant, Solenopsis geminata: A Stowaway on the First Global Trade Routes. Molecular Ecology. 24:374-388.
Manfredini, F., Lucas, C., Nicolas, M., Keller, L., Shoemaker, D.D., Grozinger, C.M. 2014. Molecular and social regulation of worker division of labor in fire ants. Molecular Ecology. 23:660-672.
Valles, S.M., Oi, D.H. 2014. Sucessful transmission of Solenopsis invicta Virus 3 to field colonies of Solenopsis invicta (Hymenoptera: Formicidae). Florida Entomologist. 97:3.
Choi, M.Y., Vander Meer, R.K. 2015. Multiple functions of fire ant, Solenopsis invicta, mandibular gland products. Physiological Entomology. doi: 10.1111/phen.12102.
Choi, M.Y., Sanscrainte, N.D., Estep, A.S., Vander Meer, R.K., Becnel, J.J. 2015. Identification and expression of the PBAN/pyrokinin gene in the sand fly Phlebotomus papatasi. Journal of Insect Physiology. 79:55-62.
Valles, S.M., Porter, S.D. 2015. Dose response of red imported fire ant colonies treated with Solenopsis invicta virus 3. Archives of Virology. doi: 10.1007/s00705-015-2520-1.
Chen, J., Rashid, T., Guolei, F., Liming, Z., Oi, D.H., Bastiaan Drees 2013. Defensive chemicals of tawny crazy ants, Nylanderia fulva and their toxicity to red imported fire ants (Hymenoptera: Formicidae). Toxicon. 76:160-166.
Shi, Q., Hu, L., Wang, W., Porter, S.D., Vander Meer, R.K., Chen, L. 2015. Workers and alate queens of Solenopsis geminata share qualitatively similar but quantitatively different venom alkaloid chemistry. Frontiers in Ecology and Evolution. 3:76.
