Location: Imported Fire Ant and Household Insects Research
2017 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
For Objective 1 research continued on the characterization of potential fire ant biological control agents as well as the genetic and semiochemical aspects of the fire ant. The social form trait (having one or many queens per colony) was used to examine the gene flow between the red and the black, imported fire ants. Using mitochondrial and microsatellite genetic markers, it was shown that social form does not impact hybridization rates or gene flow between the two invasive species in the U.S. Tropical fire ant (Solenopsis geminata) populations in Ecuador were surveyed for decapitating fly parasitoids with potential for release as self-sustaining biological control agents of invasive tropical fire ants in Hawaii and other Pacific islands. Two species of flies were found. Collections of tropical fire ants from Ecuador have been analyzed for venom alkaloids and cuticular hydrocarbons. Five unique peak profiles were found to correspond to specific geographic locations. These collections are also currently being compared to invasive populations of the Tropical fire ant in the Pacific using morphology, chemistry, and molecular biology in an effort to determine the origins of invasive fire ant populations and potential sources for compatible natural enemies. Progress has been made in understanding the biochemical processes associated with dramatic physiological changes that take place soon after mating. This research is expected to spin-off a biologically-based fire ant control method(s).
Research continued under Objective 2 on improving the integrated pest management of the invasive, tawny crazy ant on both biocontrol and insecticidal bait development. The first viral pathogen of the tawny crazy ant received a 2nd patent as a potential control agent. The virus is being evaluated for its potential as a biological control agent by comparing egg-laying rates of infected and uninfected queens. Preliminary results suggested reduced fecundity in infected queens. Various liquid and slurry bait formulations were tested against field populations of tawny crazy ants. The liquid formulation resulted in significant and visibly perceptible reductions within 1 week. To our knowledge this is the only report of such fast and perceptible field reductions of tawny crazy ants using an ant bait. However, a more efficient method(s) of dispensing the baits is a critical need. Tawny crazy ant poison sac/Dufour’s gland contents have been chemically analyzed. Attractant and aggregation bioassays will be developed to guide the isolation of compounds that may be useful in enhancement of tawny crazy ant baits.
In addition, research was conducted on subprojects related to fire ant control in irrigated sites which dovetails with subobjective 2b to improve control for the little fire ant. Three water-resistant ant bait formulations plus a standard and control bait were evaluated against red imported fire ants in the laboratory and in outdoor potted plant tests that emulated nursery irrigation conditions. Development of water resistant baits would alleviate the problem of current baits degrading when wetted. From these tests, a bait formulation developed in Taiwan and a commercially available U.S. fire ant bait were applied in a field study in the Coachella Valley of California, where fire ant populations survive in the irrigated landscapes. Results from these studies will guide testing of formulations against little fire ants, which thrive in wet, tropical climates such as Hawaii and Guam.
Relative to Sub-objective 2c, considerable progress has been made in curating and cataloging 40 years of pest ant collections. So far, more than 12,000 specimen vials and pins have been organized, databased, geolocated, and properly labeled. The next stage will be to combine collection spreadsheets and format them for uploading to several online databases, so the specimens and associated records will be easily accessible to the general scientific community for future research.
Accomplishments
1. New virus natural enemy discovered in fire ants. A fourth virus, Solenopsis invicta virus 4 (SINV-4) has been discovered in red imported fire ants, a highly invasive species in the U.S. and other countries. ARS researchers at Gainesville, Florida, have discovered the virus in South American populations of fire ants, and have since discovered that the virus is also found in fire ants in U.S. populations. SINV-4 exhibits a unique genome structure among RNA viruses leading to the creation of a new virus family, Polycipiviridae. Viruses within this family appear to infect only ant species, and thus represents a target group for searches of viruses for the biocontrol of invasive ants.
2. Four species of a parasitic ant identified. The parasitic ant, Solenopsis daguerrei, can debilitate queens of the invasive, imported fire ants and may be a potential biological control agent. Past attempts to evaluate this parasite have been stymied by the inability to transfer it to non-parasitized U.S. fire ant colonies. Population genetic analyses were conducted on 300 fire ant colonies infested with S. daguerrei collected in their native range of Argentina and Brazil by ARS scientists in Gainesville, Florida. Analyses indicated that the sampled populations of S. daguerrei are actually comprised of at least three (and likely four) previously undescribed species. Furthermore, there appears to be high degree of host specificity among these undescribed species of fire ant parasites. These results may explain unsuccessful transfer to the U.S. fire ant population and may facilitate the discovery of U.S. fire ant compatible S. daguerrei parasites in South America.
3. Texas fire ant decapitating fly not suitable for release in Hawaii and Guam. Tropical fire ants are an invasive pest in Hawaii, Guam, and many other Pacific islands. The Texas decapitating fly Pseudacteon bifidus has been studied as a potential biocontrol agent for invasive tropical fire ants. Tests have shown this fly would not be a risk for native species because it is extremely host specific. Unfortunately, ARS researchers in Gainesville, Florida, and cooperators demonstrated that this fly is too host specific because it is not sufficiently compatible with invasive tropical fire ant populations on Hawaii and Guam to justify field releases there. These results are important because they demonstrate the need to search for natural enemies from native tropical fire ant populations more closely related to those in the Pacific.
4. Pest ant control improved with water resistant bait. Over two billion dollars per year are spent on fire ant control – primarily baits. The bait carrier is a form of corn grit, which absorbs the toxicant dissolved in soybean oil. The fire ant is very efficient at finding this bait formulation and removing the soybean oil/toxicant. The main problem is that the grit carrier disintegrates under wet/moist conditions and is no longer effective. Bait labels define the restrictions on bait use depending on weather conditions, even dew on the ground. A water-resistant fire ant bait was evaluated by an ARS researcher in Gainesville, Florida, under heavy dew on the ground conditions in the field. The water-resistant bait outperformed the equivalent standard bait. The water-resistant bait can expand the utility of fire baits by eliminating current use restrictions. This new bait is badly needed for other high moisture situations and other pest ants in high rainfall areas, e.g., the little fire ant in Hawaii.
Review Publications
Pereira, R., Oi, D.H., Baggio, M.V., Koehler, P. 2017. Microbial control of structural insect pests. In: Lacey, L., editors. Microbial Control of Insect and Mite Pests. 1st edition. Salt Lake City, UT: Academic Press. p. 431-442.
Valles, S.M., Chen, Y., Firth, A.E., Guerin, D.M., Hashimoto, Y., Herrero, S., De Miranda, J., Ryabov, E. 2017. ICTV virus taxonomy profile: dicistroviridae. Journal of General Virology. 98:355-356. doi:10.1099/jgv.0.000756.
Bernard, S.J., Osbrink, W.L., Su, N. 2017. Response of the formosan subterranean termite to neighboring con-specific populations after baiting with noviflumuron. Journal of Economic Entomology. 110(2):575-583.
Valles, S.M., Chen, Y., Firth, A.E., Guerin, D.M., Hashimoto, Y., Herrero, S., De Miranda, J., Ryabov, E. 2017. ICTV virus taxonomy profile: iflaviridae. Journal of General Virology. 98:527-528. doi:10.1099/jgv.0.000757.
Vander Meer, R.K., Milne, D.E. 2017. Enhanced pest ant control with hydrophobic bait. Journal of Economic Entomology. 110(2):567-574.
Darracq, A.K., Smith, L.L., Oi, D.H., Conner, L.M., Mccleery, R.A. 2017. Invasive ants influence native lizard populations. Ecosphere. 81(1):1-17. doi:e01657. 10.1002/ecs2.1657.
Chen, J., Cantrell, C.L., Oi, D.H., Grodowitz, M.J. 2016. Update on the defensive chemicals of the Little Black Ant, Monomorium minimum (Hymenoptera: Formicidae). Toxicon. 122:127-132.
Porter, S.D., Gavilanez Slone, J.M., Valles, S.M. 2016. Solenopsis invicta virus 3: infection tests with adult honey bees (Hymenoptera: Apidae). Florida Entomologist. 99(4):729-733.
Kumar, S., Lebrun, E., Stohlgren, T., Stabach, J., Mcdonald, D., Oi, D.H., Lapolla, J.S. 2015. Evidence of niche shift and global invasion potential of the tawny crazy ant, Nylanderia fulva. Ecology and Evolution. 5:4628-4641.
Porter, S.D., Valles, S.M., Pereira, R.M. 2016. Scavenging crickets (Orthoptera: Gryllidae) transmit Solenopsis invicta virus 3 to red imported fire ant (Hymenoptera: Formicidae) colonies. Florida Entomologist. 99(4):811-812.
Shoemaker, D.D. 2016. Development of genetic markers distinguishing two invasive fire ant species (Hymenoptera: Formicidae) and their hybrids. Florida Entomologist. 99(1):117-119.
Manfredini, F., Shoemaker, D.D., Grozinger, C.M. 2016. Dynamic changes in host-virus interactions associated with colony founding and social environment in fire ant queens (Solenopsis invicta). Ecology and Evolution. 6(1):233-244. doi:10.1002/ece3.1843.
Wheeler, G.S., Steininger, M.S., Wright, S.A. 2017. Quarantine host range of Bikasha collaris; a potential biological control agent of Chinese tallowtree (Triadica sebifera) in North America. Entomologia Experimentalis et Applicata. 163:184–196.
Hertach, T., Stephane, P., Matija, G., Tomi, T., Reto, H., Hannes, B., Gernot, K., Wade, E.J., Simon, L., Chris, S., Peter, N. 2016. Complex within complex: integrative taxonomy reveals hidden diversity in Cicadetta brevipennis (Hemiptera: Cicadidae) and unexpected relationships with a song divergent relative. PLoS One. 11(11):e0165562.
Ryan, S.F., Scriber, J.M., Valella, P., Thivierge, G., Aardema, M. 2017. The role of latitudinal, genetic and temperature variation in the induction of diapause of Papilio glaucus (Lepidoptera: Papilionidae). Insect Science. doi:10.1111/1744-7917.12423.
