Project : USDA ARS

ARS Home » Southeast Area » Gainesville, Florida » Center for Medical, Agricultural and Veterinary Entomology » Imported Fire Ant and Household Insects Research » Research » Research Project #426807

Research Project: Invasive Ant Biology and Control

Location: Imported Fire Ant and Household Insects Research

2018 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
Countries in the Asia-Pacific region are very concerned about detection methods for recent fire ant incursions, primarily around ports of entry, for example in Japan sticky traps worked to detect Argentine ants. They proposed the same method to detect port incursions of fire ants. However, preliminary studies in our laboratory using a variety of commercially available sticky traps, showed a great deal of variability in the successful capture (detection) of fire ant workers. These experiments will be expanded using a wider variety sticky traps and challenging fire ant and tawny crazy ant workers. Fire ant queens inhibit the development of their sexual daughters through release of a primer pheromone. No fire ant primer pheromones have been identified to date. One of the main problems in isolating primer pheromones is the bioassay, because the effects of a primer pheromone may not be observable for many weeks. We have now developed a bioassay that will reliably provide an actionable result within one week. This development will be used to drive the isolation and identification of a fire ant primer pheromone for the first time. It is well documented that fire ant female sexuals mate only once, yet these females fly into a waiting male lek that would be expected to provide mating opportunities to multiple fire ant males. We discovered that male specific compounds are transferred to female sexuals during mating that are highly repellent to males, thus inhibiting additional males from mating to an already mated female sexual. Collaboration with an ARS researcher in Hilo, HI on the Little Fire Ant (Wasmannia auropuntata) has led to the development of a bioassay aimed at guiding the isolation and identification of the recruitment pheromone, which is envisioned to be useful in surveillance/detection and bait enhancement. A fifth virus, Solenopsis invicta virus 5 (SINV-5) has been discovered in fire ants from South America. The virus has not been detected in the U.S. population of fire ants; therefore, it may be a potential natural enemy that could be released into the U.S. fire ant population as a control agent. SINV-5 exhibits a genome structure similar to, but distinct from, SINV-1. Ants intercepted at quarantine boundaries must be rapidly identified to minimize shipping delays. In response to this need, ARS and APHIS researchers developed novel monoclonal antibodies that specifically bind a protein from S. invicta fire ant venom. This identification method has been commercialized and made available worldwide. S. invicta (red) and S. richteri (black) imported fire ants can mate and produce a viable hybrid. Novel antibodies were developed to specific S. richteri venom proteins, making it possible in combination with the S. invicta system to quickly detect the two imported fire ants and their hybrid. Progress toward the integrated pest management of the invasive tawny crazy ant was demonstrated with the use of liquid bait dispensed in small tubes around a home and natural nesting habitats. Baiting reduced the amount of insecticide applied by over 99% when compared to a single, standard insecticide spray applied to the perimeter of a home. Reductions were significant, visually apparent to the homeowner, and especially notable since it occurred during the peak seasonal population explosion of this species. Egg laying rates of tawny crazy ant queens infected with the tawny crazy ant virus were not significantly lower than uninfected queens. Field applications of a water resistant bait in irrigated landscapes in California did not result in significant differences on fire ant populations from standard bait. Fire ants were observed foraging on both bait types after irrigation. However, evaluations may have been confounded by the difficulty in sampling in the desert climate. Exposure of little fire ants, an invasive ant plaguing the Islands of Hawaii and Guam, to standard imported fire ant bait that was soaked in water resulted in the elimination of laboratory colonies. This suggested that wet ant bait may be effective in wet climates if it is not washed away by rain.

Accomplishments
1. Red imported fire ant detection device developed and commercialized. Fire ant introductions are a constant problem at ports and at quarantine boundaries. Ants detected on cargo must be rapidly identified to minimize shipping delays. In response to this need, a rapid, field-portable kit capable of identifying fire ants by untrained personnel was developed by ARS researchers at Gainesville, Florida and APHIS researchers at Biloxi, Mississippi. The kit is based on the lateral flow immunoassay technology familiar in home pregnancy tests. The test provides an answer within 10 minutes without any prior training or knowledge. Agdia, Inc. (https://orders.agdia.com/invictdetect-isk-49700-0010) has acquired the Biological Material License for the monoclonal antibodies in the test from the USDA and has begun commercially manufacturing the kits under the trade name, INVICTDETECT.

2. New Solenopsis species invades Hawaii. A single ant was taken from a flower basket before the basket was put in a freezer to kill nestmate ants. The ant was tentatively identified in Hawaii as Solenopsis invicta. Since S. invicta is one of the worst world-wide invasive pest ants and it has not established in Hawaii, it was important to get positive confirmation. The single ant specimen, in 70% ethanol, was sent to ARS researchers at Gainesville, Florida, where a combination of biochemical and molecular techniques was applied to identify the ant as Solenopsis xyloni, a native fire ant in the continental USA, and not S. invicta. The molecular and biochemical tools were made possible through decades of ARS research to develop novel identification methods for species in this ant group that is very difficult to separate using classical taxonomy. Global trade is spreading S. invicta to other countries in the Asia-Pacific area where these tools will continue to be in demand.

U.S. DEPARTMENT OF AGRICULTURE

Imported Fire Ant and Household Insects Research: Gainesville, FL