Location: Imported Fire Ant and Household Insects Research
2016 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
Analysis of eight gene libraries (from fire ant collections in Argentina) for new pathogens, was continued from last year. Fire ant genes have been subtracted from the libraries, leaving only pathogen genes. Large numbers of possible natural enemies have been tentatively identified. These sequences require further investigation to establish their relationship to the ant (pathogen or not). Research continues on genome sequence data from 187 male fire ants. A large-scale study continues to investigate the possibility of segregation distortion, which is predicted as another selfish genetic trait of the supergene that favors its persistence in wild populations despite its detrimental effects on individual ants. Host specificity tests with the fire ant virus, SINV-3, showed that it was incapable of infecting honey bees and domestic crickets. These results are important because they strengthen the conclusion that release of this virus as a biocontrol agent will not have unintended consequences. Laboratory studies with domestic crickets showed that the SINV-3 virus can be mechanically vectored between fire ant colonies in the guts of scavengers which eat dead infected ants and are then consumed themselves by fire ants from another colony. These results establish a likely mode of transmission for SINV-3 from one imported fire ant colony to another. Studies of the decapitating fly Pseudacteon bifidus were concluded after tests showed that target tropical fire ant populations in Hawaii, Guam, and the Galapagos Islands would likely not be suitable hosts, even though tropical fire ants from Texas and Florida were suitable. Other species of Pseudacteon decapitating flies in Mexico and Ecuador that parasitize tropical fire ant populations will be evaluated on Florida populations. Samples of the decapitating fly, Pseudacteon nocens, were collected from red imported fire ant sites in Texas, then released at sites in Mississippi and Florida. Flies were recovered from the Florida site 6 months after release. Monitoring will continue to confirm, or not, establishment of the flies at these two release sites. A large helium balloon system has been constructed that will permit evaluation of the effects of male and female sexual semiochemicals for their effects during mating flights. Also 182 colony samples from Argentina were analyzed for venom alkaloids and cuticular hydrocarbons, which had been shown to be very good taxonomic characters. Three distinct chemotypes were identified, one of which matched Solenopsis (S.) invicta in the USA. These results can impact the unit’s search for pathogens in South America. The exocrine gland chemistry of tawny crazy and the little fire ant were investigated for glandular source and chemical structures and will be probed for function. The first viral pathogen of the invasive tawny crazy ant was characterized and received a patent as a potential control agent. The full-length genome of the virus, Nylanderia fulva virus 1 (or NfV-1), was obtained and found to form a new virus family composed solely of ant-infecting viruses (proposed name: Solinviviridae). NfV-1 is easily transmitted to uninfected colonies by baiting techniques. The virus appears to infect all life stages of the ant, but appears to only replicate in the larval stage. Host specificity tests showed that NfV-1 appears to only infect tawny crazy ants. Phenotypic effects of the virus are being evaluated for its potential as a classical biological control agent and/or biopesticide. The effective dose range of dinotefuran in a liquid bait formulation against tawny crazy ant colonies was found to be 100X. This dose range is 10 times wider than the effective commercial fire ant bait active ingredient hydramethylnon (10X) when tested against red imported fire ants. The identification of an efficacious bait active ingredient is critical in developing baits for tawny crazy ant integrated management. ARS fire ant collections in North America and South America (25 yr span) have been entered into spreadsheets and geo-referenced. This information will be combined with a similar database of collections from the Fundación para el Estudio de Especies Invasivas (FuEDEI) in Argentina and shared on web-based databases to be generally available to experts worldwide.
Accomplishments
1. Fire ant field identification kit developed. The Imported Fire Ant (IFA) Quarantine has been in place since 1958, regulating the interstate movement of certain commodities in an effort to reduce spread of imported fire ants. Rapid ant identification at border inspection stations and ports is critical to facilitating trade and commerce, and currently is not always possible due to small specimen numbers and difficulty in differentiating between native and imported ants through morphological characteristics. Researchers from ARS, Gainesville, Florida, and APHIS, Biloxi, Mississippi, have developed a field-portable, rapid detection kit to identify imported fire ants. The kit requires no special training or equipment and can be completed in 10 minutes. APHIS plans to use the kits at interdiction sites to enforce the quarantine. In addition, regulatory agencies from other countries are interested in adopting the technology.
2. Host specificity tests completed for the SINV-3 fire ant virus. The SINV-3 virus can be lethal to fire ants, but before it can be used as a biopesticide or a self-sustaining biocontrol agent for imported fire ants, it must be tested for host specificity. ARS scientists in Gainesville, Florida, in cooperation with a colleague at the University of Florida conducted a series of laboratory infection tests, which demonstrated that SINV-3 does not infect or replicate in either honey bees or house crickets. These and other specificity tests are important because they demonstrate that the SINV-3 virus is a highly host specific pathogen which is only capable of infecting imported fire ants.
None.
Review Publications
Oi, D.H., Porter, S.D., Valles, S.M. 2015. A Review of the Biological Control of Fire Ants. Myrmecological News. 21:101-116.
Porter, S.D., Valles, S.M., Gavilanez Slone, J.M. 2015. Long-term efficacy of two cricket and two liver diets for rearing laboratory fire ant colonies (Hymenoptera: Formicidae: Solenopsis Invicta). Florida Entomologist. 98(3):991-993.
Valles, S.M., Wetterer, J.K., Porter, S.D. 2015. The red imported fire ant (Solenopsis invicta) in the West Indies: distribution of natural enemies and a possible test bed for release of self-sustaining biocontrol agents. Florida Entomologist. 98(4):1101-1105.
Valles, S.M., Oi, D.H., Becnel, J.J., Wetterer, J.K., Lapolla, J.S., Firth, A.E. 2016. Isolation and characterization of Nylanderia fulva virus 1, a positive-sense, single-stranded RNA virus infecting the tawny crazy ant, Nylanderia fulva. Virology. 496:244-254.
Allen, C., Valles, S.M. 2015. Successful transcription but not translation or assembly of Solenopsis invicta virus 3 in a baculovirus-driven expression system. Florida Entomologist. 98(3):943-949.
Choi, M.Y., Ahn, S., Park, K., Vander Meer, R.K., Carde, R.T., Jurenka, R. 2016. Tarsi of male heliothine moths contain aldehydes and butyrate esters as potential pheromone components. Journal of Chemical Ecology. 42(5):425-432. doi: 10.1007/s10886-016-0701-3.
Sosso, D., Luo, D., Li, Q., Sasse, J., Yang, J., Gendrot, G., Suzuki, M., Koch, K., Mccarty, D., Chourey, P., Rogowsky, P., Ross-Ibarra, J., Yang, B., Frommer, W. 2015. Seed filling in domesticated maize and rice depends on SWEET-mediated hexose transport. Nature Genetics. 47(12):1489-1496.
Coates, B.S., Poelchau, M.F., Childers, C., Evans, J.D., Handler, A.M., Guerrero, F., Skoda, S.R., Hopper, K.R., Wintermantel, W.M., Ling, K., Hunter, W.B., Oppert, B.S., Perez De Leon, A.A., Hackett, K.J., Shoemaker, D.D. 2015. Arthropod genomics research in the United States Department of Agriculture-Agricultural Research Service: Current impacts and future prospects. Trends in Entomology. 11(1):1-27.
Poelchau, M.F., Coates, B.S., Childers, C., Evans, J.D., Hackett, K.J., Shoemaker, D.D. 2016. Agricultural applications of insect ecological genomics. Current Opinion in Insect Science. 13:61-69. doi:10.1016/j.cois.2015.12.002.
Suckling, D.M., Stringer, L.D., Jimenez-Perez, A., Bunn, B., Vander Meer, R.K. 2016. Can communication disruption of red imported fire ants reduce foraging success. Myrmecological News. 23:25-31.
Valles, S.M., Strong, C.A., Callcott, A.A. 2016. Development of a lateral flow immunoassay for rapid field detection of the red imported fire ant, Solenopsis invicta (Hymenoptera: Formicidae). Analytical and Bioanalytical Chemistry. 408(17):4693-4703.
