Research Project: Management of Fire Ants and Other Invasive Ants

Location: Imported Fire Ant and Household Insects Research

2022 Annual Report

Objectives
1. Conduct studies on fire ant biology to develop new and improved surveillance and control strategies as part of an integrated pest management program. 1.1. Develop natural enemies of fire ants as classical biological control agents or biopesticides by characterizing their life cycle, evaluating their effectiveness, determining host specificity, developing methods for production and release, and formulating as biopesticides. 1.2. Determine how irrigation affects fire ant bait efficacy. 1.3. Develop novel biologically-based fire ant control by identifying the behavioral and semiochemical underpinnings of fire ant mating flights and colony establishment. 1.4. Identify key biological processes in fire ant life stages that may be susceptible to disruption. (vacant Molecular Biologist) 1.5. Determine and quantitate fire ant traits that contribute to their ability to survive the harsh conditions associated with accidental transport over long distances and/or establishing and expanding infestations at the invasion front. (vacant Entomologist) 2. Develop new surveillance and control strategies for crazy ants and other invasive pest ants. 2.1. Employ metagenomics techniques and next generation sequencing technologies to discover potential natural enemies of the little fire ant. 2.2. Develop an effective baiting strategy for the control of tawny crazy ants. 2.3. Investigate the homology of pheromone systems that are well understood for S. invicta, but relatively unknown in the little fire ant and the tawny crazy ant. 2.4. Identify key biological processes of little fire ants and/or tawny crazy ants that can be exploited and developed as novel control methods. (vacant Molecular Biologist) 2.5. Determine and quantitate little fire ant, tawny crazy ant, and other ant species traits that contribute to their invasive success, e.g., metabolic rates. (vacant Entomologist)

Approach
1.1 Integration of any new natural agent into a fire ant control program will require the satisfactory completion of studies in host specificity, predicted-efficacy, virulence, mode of action/transmission, formulation/rearing and field release methodologies. 1.2 Water resistant and standard fire ant bait formulations exposed to irrigation will be evaluated for efficacy against fire ant colonies. The effect of bait application methods (piled vs broadcast) on improving bait tolerance to irrigation will also be assessed. 1.3 Behavioral and semiochemical underpinnings of fire ant mating flights and colony establishment will be examined by determining the behavior of alates to pyrazines with olfactometer bioassays and in-flight lek sampling. Male produced tyramides will be further evaluated for physiologicfal functions related to multiple mating and rapid wing loss. 1.4 The approach of this sub-objective will be defined by the scientist filling the vacant Molecular Biologist position. 1.5 The approach of this sub-objective will be defined by the scientist filling the vacant Entomologist position. 2.1 Little fire ants from across the native and introduced ranges will be collected and used as RNA source material to create cDNA expression libraries. Detailed bioinformatics analysis of resulting NGS data will allow us to identify potential microsporidia, fungi, viruses, protists, and non-hymenopteran eukaryotic parasites. Sequence leads will be verified by molecular analysis of little fire ant colonies sampled within and outside the native ranges. 2.2 Consumption and temporal feeding patterns by tawny crazy ants (TCA) on liquid sucrose bait containing a slow-acting toxicant will be compared to bait containing a fast-acting toxicant. Time lapse photography will be used to document temporal feeding patterns over 72 hours. TCA feeding patterns will be used to design liquid bait dispensers such as alginate hydrogel carrier and presented in a compostable dispenser. 2.3 Systematically evaluate exocrine glands in TCA and little fire ant (LFA) workers and queens for phenotypic effects, e.g. attraction, repellency, alarm, and recruitment using behavioral bioassays. Attraction will be investigated first, using a Y-tube olfactometer bioassay to guide the isolation of active compounds. Attractants can enhance baits and improve monitoring systems. 2.4 The approach of this sub-objective will be defined by the scientist filling the vacant Molecular Biologist position. 2.5 The approach of this sub-objective will be defined by the scientist filling the vacant Entomologist position.

Progress Report
Nursery stock (in burlap root balls) transported outside the Animal and Plant Health Inspection Service (APHIS) Federal Imported Fire Ant quarantine area must be certified free of fire ants. Improvements in burlap root ball treatments are needed. The effectiveness of water-resistant spatter and granular bait formulations and application methods on irrigated, balled and burlap root ball plants reduced fire ant populations, but inconsistently eliminated fire ant colonies. Thus, applying baits to root balls were not effective in controlling fire ants that meet the fire ant quarantine standards. Evaluation of non-repellent insecticide spray applications to the exterior of root balls as an alternative to baiting is in progress (Project Plan Objective 1). Significant progress was made by ARS scientists at Gainesville, Florida on all objectives of the Mission Critical Research project titled “Fire Ant IPM in the Coachella Valley, California”. With assistance from the Coachella Valley Mosquito and Vector Control District staff, 1) Fire ant mating flight activity under desert climate conditions is now being monitored weekly. 2) Surveys on the spread of fire ant biological control agents, Solenopsis invicta virus-3 and two species of fire ant decapitating phorid flies released in 2014, have now spread at least a half a mile beyond release sites. The survivorship and spread are significant due the patchy distribution of fire ant populations and extreme heat in the desert climate. 3) A field study comparing efficacy of fire ant bait applications following the standard practice of withholding irrigation versus maintain the normal irrigation schedule did not result in significant differences in control. This indicates that bait applications can be made without disrupting normal irrigation, thus making fire ant operations more efficient. This subordinate project is relevant to fire ant surveillance and control aspects of Project Plan Objective 1. Derivatives of RNA interference (RNAi) constructs have been shown to exert greater mortality effects on fire ant workers, than non-derivatized constructs, suggesting that the derivatized RNAi is more stable toward gut enzyme degradation and are less polar making it easier for them to cross from the gut to the hemolymph. This research showed excellent potential for the proprietary derivatization methodology. Consequently, a NIFA Phase 2 SBIR grant was applied for and approved for funding. This methodology is using the economically important fire ant as the model organism (Project Plan Objective 1). However, a spinoff is expected for other invasive ants, such as the tawny crazy ant and the little fire ant (Project Plan Objective 2). Several small peptide antagonists to essential G-Protein Coupled Receptors were isolated and identified using a unique screening/isolation process. The active peptides are readily synthesized. The most bioactive are currently being evaluated against worker fire ants under laboratory conditions to determine optimal concentrations and formulations. This research targets imported fire ants (Project Plan Objective 1) and is associated with a NIFA SBIR Phase 1 grant. This species-specific technology can be applied to the tawny crazy ant, the little fire ant (Project Plan Objective 2), and other pest insects. The methodology quickly identifies strong agonist/antagonists that interfere with key insect physiological processes. There has been considerable commercial interest in this technology. A novel control method for fire ants was discovered and patented from research on the mechanism by which a queen's reproductive daughters quickly free themselves from their mother/queen's suppression of their reproductive development. When the active compound(s) is fed to laboratory fire ant colonies, worker and queen mortality results; however, the ingestion of the active ingredient was very low, especially with field colonies. Through a CRADA funded by a National Science Foundation (NSF) Phase 1 SBIR grant we are investigating methods to increase the acceptability of the active ingredient(s). Success is expected to result in the first new fire active ingredient in 15 years. This research targets imported fire ants in support of Project Plan Objective 1. However, spin-off to other pest ant species (Project Plan Objective 2), or other pest insects is expected. ARS scientists from Gainesville, Florida, have collected ants from 180 nests of the red imported fire ant, Solenopsis invicta, along a transect from southern Florida to northern Georgia. These collections are part of a funded MTRA with the South Korean Animal and Plant Quarantine Agency. Collections will continue up to November 30, 2022. The collections are part of larger project aimed at being able to identify the origin of any Solenopsis intercepted at South Korean or other ports around the world. (Project Plan Objective 1). The frequency and intensity of foraging by the invasive, tawny crazy ant on liquid baits was documented with customized trail cameras that record time-lapse images in the field. Tawny crazy ant feeding on liquid bait containing a fast acting toxicant was significantly less than the slow acting bait and the control. The SEA statistician provided excellent guidance on analyzing feeding patterns. A study has been initiated to examine the effects of the fast and slow-acting toxicant on field colonies of this invasive ant. In addition, tawny crazy ant feeding patterns on an alginate hydrogel carrier for a liquid ant bait will be assessed to help guide bait development for tawny crazy ants. (Project Plan Objective 2) Analysis of tissue ratios of stable isotopes of carbon (13C/12C) and nitrogen (15N/14N) is a standardized way of quantifying the feeding ecology and trophic interactions of invasive and native ants, but we lack an understanding of how these ratios vary in dispersing queens relative to workers. Variation in isotope ratios among queens and workers of a variety of invasive and native species under field conditions are being examined by ARS researchers in Gainesville, Florida and Brookings, South Dakota. The results will shed light on invasive ant queen metabolism, survival, and dispersal, and help develop novel methods for rapidly determining ant feeding ecology. (Objectives 1.5, 2.5) To determine how geography and climate impact the timing of ant mating and the release of dispersing queens, historical records of ant mating events in the contiguous U.S. were analyzed from digitized records in an open-access database of ant museum specimens. Ant mating seasons were found to occur later at higher latitudes and elevations, and have been occurring earlier in recent years, likely due to warmer temperatures under climate change. Twenty-five percent of native species have been mating earlier in recent years, but none of the invasive species with enough data showed recent changes in mating season. (Objectives 1.5, 2.5) To determine the timing of ant mating flights in agricultural landscapes and relate it to changes in climate, weather, and land use, ARS researchers in Gainesville, Florida and Urbana, Illinois collected flying ant queens and males captured by the USDA Aphid Suction Trap Network in 2020 and 2021 and are currently collecting those from 2022. These ants, collected from 33 agricultural research sites across 10 states, represent perhaps the most comprehensive large-scale dataset of ant flight phenology ever collected on Earth. The dataset will be developed to provide a snapshot of when invasive and native ants mate across much of the U.S., measure how that has changed compared to 20th century baselines and predict how ant mating seasons and invasive ant distributions may change under projected future climates. (Objectives 1.5, 2.5) By performing a simulated drought experiment at the Kellogg Biological Station LTER in Michigan, ARS researchers from Gainesville, Florida and researchers from Michigan State University measured how projected future climates will impact invasive and native ant foraging activity in agricultural systems. Invasive pavement ants Tetramorium immigrans were insensitive to drought conditions, foraging at equally high levels under drought and control treatments. Native cornfield ants, Lasius neoniger, in contrast, showed high sensitivity to drought, and increased their average foraging activity by 30-40% under drought conditions. Work is ongoing to determine how these effects vary under different agricultural treatments and whether they impact rates of pest suppression in crops. (Objective 2.5).

Accomplishments
1. A forty-year-old mystery of reproductive development in new fire ant queens is solved. Fire ant queens use a pheromone to inhibit reproductive development in their daughters while in the colony. When conditions are right the unmated daughters fly from a nest, mate with males, and then the new queens immediately begin reproductive development and attempt to start new colonies on the ground. How this rapid initiation of reproductive development is accomplished has been a mystery for over 40 years until ARS researchers at Gainesville, Florida, and collaborators from Foresight Science and Technology, Virginia Military Institute, and Ohio State University discovered that fire ant males produce a chemical class called tyramides that are passed on to the daughters during the mating process. They also determined that the daughters produce a specific enzyme that converts tyramides to tyramine which causes accelerated reproductive development, essential to survival of the new colony. This work will be a model for future research in this area, and was reported in Nature Communications, where it has generated significant attention (93rd percentile interest for all outputs of the same age). In addition, these discoveries have already led to a possible novel control method for fire ants (Patent issued).

2. Fire ant colonies eliminated after inoculation with a fire ant virus. The red imported fire ant was introduced into the United States in the 1930s and currently infests about 300 million acres. The fire ant causes $8 billion in annual control costs and losses to many economic sectors, including livestock and agricultural production and poses a serious threat to human health. Biological control is widely considered the most sustainable method for the regional control of fire ants. Using gene sequence identity/homology approaches, ARS scientists in Gainesville, Florida, discovered and characterized Solenopsis invicta virus 3, which specifically infects fire ants. They found the virus to be a virulent pathogen of fire ant colonies under laboratory conditions where it consistently killed colonies and was highly transmissible. Introductions of this virus into fire ant nests in the field caused reductions in the size and number of fire ant nests. It also persisted for over 20 months and spread to adjacent uninoculated colonies. This is the first documentation of a fire ant virus eliminating fire ant colonies under field conditions and demonstrates that this host specific, self-sustaining virus can be an important, biological control agent of the widespread, stinging, invasive, fire ant.

3. Organic agriculture has higher pest suppression by ants in the U.S. Corn Belt. Organic agriculture has the potential to reduce greenhouse gas emissions, pollutant runoff, and biodiversity loss compared to conventional agriculture, but the long-term effects on many organisms remain unknown. ARS scientists from Gainesville, Florida, and Michigan State University examined 31-year-long landscape experiments to test the impacts of organic agriculture on ant communities and the ecosystem services they provide to crops. Despite supporting mostly the same species, organic crops experienced higher potential pest suppression provided by ants, due to differences in the timing of ant foraging. Ants in conventional crops mostly foraged late in the growing season, when they are less likely to be useful in suppressing pests of developing crops. Ants in organic crops, in contrast, were active throughout the growing season, with most foraging taking place early in the season when crops were still developing. The results showed that by this standard organic agriculture supported twice as much ant-mediated pest suppression potential as conventional agriculture.

4. Fire ant bait remains effective after irrigation. The red imported fire ant is an invasive pest of agricultural, urban, and natural areas. It is also considered a public health pest due to its painful sting. This ant can be efficiently controlled by commercial fire ant baits which typically contain corn grit, an ingredient that allows the bait to be easily applied and readily collected by ants. Traditionally it is thought that the corn grit degrades when exposed to rain or irrigation and fire ant control does not occur because the ants do not feed on wet bait. As a result, water-resistant fire ant baits have been developed that either replace or modify the corn grit. Research conducted by an ARS scientist in Gainesville, Florida, and collaborators from APHIS, and the Coachella Valley Mosquito and Vector Control District in California determined that both standard commercial fire ant bait and water-resistant baits that have been soaked in water in the laboratory, as well as exposed to sprinkler irrigation in landscapes, can still effectively control fire ants. Because water-resistant fire ant baits are not readily available in the U.S., knowledge that standard fire ant baits can withstand sprinkler irrigation should allow land managers and groundskeepers more flexibility in scheduling fire ant treatments.

5. Prairie strips benefit pollination and biodiversity in the U.S. Corn Belt. The establishment of strips of restored prairie vegetation within row crop fields is an increasingly popular tool for diversifying agricultural landscapes in the Midwestern U.S. Prairie strips reduce soil erosion, improve water quality, and support native biodiversity. But it is unclear how prairie strips interact with other agricultural practices and how far their benefits propagate into surrounding fields. ARS scientists from Gainesville, Florida, Michigan State University, the University of Puerto Rico, and Hawai’i Pacific University addressed this by studying biodiversity and ecosystem services in newly established prairie strips within a 32 year-long agricultural landscape experiment. They found that during the first two years after planting prairie strips, proximity to strips increased dung beetle abundance, spider abundance and richness, soil active carbon, decomposition rates, and pollination rates, and that the effects got stronger over time. Some effects interacted with other agricultural practices, such that fields with both prairie strips and reduced fertilizer and pesticide use had higher butterfly and spider abundance and higher pollination rates. The results demonstrate the potential for prairie strips to rapidly support enhanced biodiversity and ecosystem services while still maintaining crop yields.

Review Publications
Vander Meer, R.K., Chinta, S.P., Jones, T.H., O'Reilly, E.E., Adams, R.M. 2021. Male fire ant neurotransmitter precursors trigger reproductive deveopment in females after mating. Nature Communications. 4:1-11. https://doi.org/10.1038/s42003-021-02921-5.
Vander Meer, R.K., Chinta, S.P., Jones, T.H. 2022. Novel alkaloids from the fire ant, Solenopsis geminata. Naturwissenschaften. 109(15):1-6. https://doi.org/10.1007/s00114-022-01786-w.
Ascunce, M.S., Vander Meer, R.K., Chinta, S.P., Ogura-Yamata, C., Oishi, D. 2022. Genetic and chemical profiling of Solenopsis spp. (Hymenoptera: Formicidae) intercepted in Hawaii. Florida Entomologist. 105(1):91-94. https://doi.org/10.1653/024.105.0114.
Oi, D.H., Atchison, R.A., Chuzel, G., Chen, J., Henke, J.A., Weeks, R.D. 2022. Effect of irrigation on the control of red imported fire ants (Hymenoptera: Formicidae) by water-resistant and standard fire ant baits. Journal of Economic Entomology. 115(1):266-272. https://doi.org/10.1093/jee/toab242.
Traylor, C.R., Ulyshen, M.D., Wallace, D., Loudermilk, E.L., Ross, C.W., Hawley, C., Atchison, R.A., Williams, J.L., Mchugh, J.V. 2022. Compositional attributes of invaded forests drive the diversity of insect functional groups. Global Ecology and Conservation. 35(1):e02092. https://doi.org/10.1016/j.gecco.2022.e02092.
Humprhines, A.R., Ascunce, M.S., Goss, E.M., Helmick, E.E., Bartlett, C.R., Myrie, W., Barrantes, E.A., Zumbado, M.A., Bustillo, A.E., Bahder, B.W. 2021. Genetic variablity of Hapalaxius crudus, based on the 5' region of the cytochrome c oxidase subunit 1 gene shed light on epidemology of palm lethal decline phytoplasmas. Phytofrontiers. 1:127-134. https://doi.org/10.1094/PHYTOFR-12-20-0048-R.
Helms IV, J.A., Smith, J., Clark, S., Knupp, K., Haddad, N.M. 2021. Ant communities and ecosystem services in organic versus conventional agriculture in the U.S. Corn Belt. Environmental Entomology. 50(6):1276-1285. https://doi.org/10.1093/ee/nvab105.
Kemmerling, L.R., Rutkoski, C.E., Evans, S.E., Helms IV, J.A., Cordova-Ortiz, E.S., Smith, J.D., Vasquez-Custodio, J.A., Vizza, C., Haddad, N.M. 2022. Prairie strips and lower land use intensity increase biodiversity and ecosystem services. Frontiers in Ecology and Evolution. 10(833170):1-18. https://doi.org/10.3389/fevo.2022.833170.
Oi, D.H. 2020. Seasonal prevalence of queens and males in colonies of tawny crazy ants (Hymenoptera: Formicidae) in Florida. Florida Entomologist. 103(3):415-417. https://doi.org/10.1653/024.103.0318.
Oi, D.H., Lucky, A., Liebowitz, D.M. 2022. Response of Wasmannia auropunctata, (Hymenoptera: Formicidae) to water-soaked imported fire ant baits. Florida Entomologist. 105(2):108-114. https://doi.org/10.1653/024.105.0202.
Valles, S.M., Oi, D.H., Weeks, Jr, R.D., Addesso, K.M., Oliver, J.B. 2022. Field evaluation of Solenopsis invicta virus 3 against its host Solenopsis invicta. Journal of Invertebrate Pathology. 191:107767. https://doi.org/10.1016/j.jip.2022.107767.
Valles, S.M. 2021. Diet with sucrose ameliorates Solenopsis invicta virus 3 (Solinviviridae: Invictavirus) infection in Solenopsis invicta (Hymenoptera: Formicidae) worker ants. Florida Entomologist. 104(3):239-242. https://doi.org/10.1653/024.104.0314.