Location: Biological Control of Pests Research
2023 Annual Report
Objectives
Objective 1: Discover new bioactive compounds and approaches to improve control of fire ants and other invasive ants.
Sub-objective 1A: Discover naturally occurring and environmentally benign synthetic compounds as toxins for invasive ant control.
Sub-objective 1B: Discover naturally occurring and synthetic compounds as behavior-modification agents for invasive ant control.
Objective 2: Develop new management strategies using genetic-based technologies for fire ant and invasive ant control.
Sub-objective 2A. Predict gene function and utilize existing genetic resources to test and develop invasive ant-specific assays, leading to control methods and products.
Sub-objective 2B. Develop gene disruption assays and approaches for mitigating the impact of invasive ants.
Sub-objective 2C. Identify and develop novel microbiome assays, and approaches for mitigating the impact of invasive ants.
Objective 3: Develop new and improved biorational pesticide delivery systems to control fire and other invasive ants.
Approach
Effective and environmentally benign ant toxins will be searched from various sources, including plants and other ants. In addition to ant toxins, we will search for behavior-modifying compounds that affect ant foraging and feeding using conventional bioassay-guided approaches and reverse chemical ecology approaches. These compounds can be very useful in improving ant developing control products. In the effort to develop gene disruption methods and materials, database comparisons will be conducted to identify target genes. Functional genomic techniques are essentially undeveloped in ants. We will begin by studying the genetics of key physiological processes within the colony. Because gene disruption experimentation is not standardized in ants, we will seek a visible phenotype, preferably non-lethal and visible in larvae, to provide an experimental positive control. We will initially focus on genetic disruption strategies which can disable the key physiological process of larval fitness and development. We will develop and utilize new molecular tools to validate, quantify, and develop genetic compounds and preparations that interfere with colony survival and resource exploitation. Additionally, preliminary studies identified unique viruses present in our regional populations of red imported fire ants. These discoveries need to be leveraged into ant-specific pathogens. The field of ant genomics and microbiome research has blossomed over the past 10 years. Individualized gene function studies, focusing on social form, chemosensory systems, neuropeptides, and oogenesis, have begun to shed light on the complex relationships between genes and phenotypes and behaviors. RNA interference studies have been performed on both fire ants and tawny crazy ants. A novel family of viruses was characterized. These investigations will lead innovation into new and improved control methods to mitigate invasive and destructive ants. Active ingredients or existing biorational pesticides will be used in developing new or improving existing biorational insecticide delivery systems. We will continue our effort in searching for adjuvants and synergists for improving the efficacy of mound treatment for fire ant control and spray treatment for tawny crazy ants. We will develop new water-resistant ant bait carriers using easily available local materials. Bait matrix will be developed and optimized for tawny crazy ants for both granular bait and liquid bait stations. Bait acceptance will be improved by using attractants and feeding stimulants. Bait selectivity will be enhanced by using selective repellants that attract targeted ants but repel non-targeted ants. We will continue our research on identifying effective synergists and surfactants for the final formulations.
Progress Report
Deformed wing virus (DWV), a major honey bee pathogen found throughout the world. The classic honey bee-like symptoms of deformed wings was observed in the laboratory and field colonies of the red and black imported fire ants. The presence and replication of DWV in the symptomatic ants were verified. This is the first report of DWV-like symptoms in ants, indicating that fire ants may be detrimentally affected by this widely distributed bee virus. A multi-county survey is conducting to determine the occurrence of this virus in red, black and hybrid imported fire ants. The whole sequence of this virus is under investigation to evaluate the potential of using this virus in managing fire ants.
Continued working on improving fire ant specificity. A selective feeding deterrent was identified from fire ant venom, which can be added into fire ant bait to make the bait unattractive to other ants but not fire ants. This is an innovative way to improve the bait specificity. A patent application covering this work was filed in December of 2022.
Identified fire ant repellents from plant-derived essential oils (EOs). Gurgen balsam EO (Dipterocarpus turbinatus) and Pachouli EO (Pogostemon cablin). A bioassay-guided fractionation approach was employed to isolate active compounds from these two EOs. The sesquiterpene compound, copaene, was isolated from Gurgen balsam EO as the primary active compound, while patchoulol, a sesquiterpene alcohol, was identified to be re responsible for the observed activity of Pachouli EO. Structural modification of these two compounds is currently underway to identify more chemically stable and biologically relevant compounds.
Identified carvacrol and thymol as potent fire ant repellents and structure activity relationship studies are ongoing. Carvacrol and thymol are the primary constituents of thyme EOs and other EOs from multiple plants. Eleven synthetic analogues were prepared for structure and repellency activity relationship studies, along with additional 35 synthetic analogues from commercial sources. The result suggests that carvacrol and thymol and their analogues are promising candidates for fire ant control.
Synthesized geranyl acetate analogues. Geraniol, a sesquiterpene alcohol present in many plants, exhibits insecticidal and repellent properties. Geranyl acetate was identified from the lemongrass EO (Cymbopogon citratus) as the primary active compound in the repellent screening assays. Five geranyl derivatives with amine containing structural moieties were synthesized, which are more chemically stable. Five structural analogues of geranyl acetate were required from commercial sources. Bioassay result indicates that seven compounds are potent repellant against imported fire ants.
ARS scientists in BCPRU are the first to discover that fire ants feed their nestmates with their own venom. Synthesized structural analogues of fire ant venom alkaloids with even numbers of carbons in the long alkyl chain were synthesized. These compounds will be used in studying the circulation of venom in the fire ant colonies.
Synthesized three oxo-fatty acids. As fire ant attractants, these compounds or their structural analogues may be used to improve fire ant efficacy. Imported fire ants has recently begun expanding northward into Kentucky, which has caused several counties there to be placed under quarantine for export of horticultural products. ARS scientists helped in determining the species by profiling venom alkaloid and cuticular hydrocarbon. Thus far, black imported fire ants and hybrid imported fire ants were documented in several counties in Kentucky. A peer review article documenting this spread was published.
The range of the two-spined trap jaw ant, Odontomachus haematodus, an invasive species, has been observed to been expanding in recent years. A survey to map its current distribution will be conducted in the next year. The Mississippi Entomological Museum has also provided numerous ant identifications to USDA port identifiers this year, and hosted one identifier for a short course on native ant ID.
Survey was conducted on ants of grasslands in northwest Arkansas: This is the first year of the project to survey ants of Ozark grasslands, starting with the Boston Mountains. The first step was to survey published literature, databases, and museum records to determine which species are currently known from the region. This step has been completed and results were presented at the Mississippi Entomological Association's Annual Meeting in Starkville, MS. The next step is to begin field surveys. This aspect has just taken off. Field sites have been chosen and a few sampled. The next year of the project will emphasize field collections and identifications. Further, the distribution of fire ants (Solenopis invicta, a recent invader in the region), is being surveyed.
The overwintering micro-habitat preference of tawny crazy ants was investigated. Though originating from a region of South America with little to no sub-freezing temperatures, this species exhibits an ability to withstand short periods of sub-zero exposure. It has been experimentally shown to detect less than 2 degree C differences and will exhibit thermotaxis to escape unfavorable temperatures. By examining this species’ movement and behavior in a natural system during winter conditions, we may be able to verify to what extent this ant is likely augmenting its inherent cold tolerance.
Another set of trapping data (Nov. 2022-Mar. 2023) was collected using the modified arboreal ant trap design. An initial trapping had been done from September 2021-April 2022 in an area with a known population of tawny crazy ants. Data is still being compiled and analyzed. Non-target insect specimens caught in the arboreal traps included many beetles in the family Curculionidae. A new state record for an introduced species was collected and resulted in a publication.
Using a re-designed subterranean ant trap, a pilot trial was carried out from March - June 2022, with the traps re-set from Oct. 2022 to March 2023, providing catch data at the four depth ranges. Tawny crazy ants were found periodically at all depths, to at least 47 cm, the lower limit of the trap design. The soil temperature at each depth range was also recorded at each sample collection time point.
Continue working on the ecology of invasive and native ants. Grassland communities represent major biodiversity hotspots across the United States. Among these grassland types is the short-leaf pine savanna, a major historical habitat along the Cumberland Plateau. The Cumberland Plateau’s grasslands are under threat due to land use changes such as urbanization and land conversion to pasture and hardwood forests. A study aiming to better understand the community ecology of ants on the Cumberland Plateau was conducted using powerlines as a comparison to degraded and historic habitats. Ants have a preference between open sites and forested sites, a separation of 44.5% on a DCA. The Simpson diversity places the short-leaf pine savanna significantly lower than adjacent forest.
Provided ant fauna identification services for a project investigating the change in the ant fauna of rapid growth pulpwood plots. The method of collection is pitfall trapping. So far, there have been a total of 116,442 individual ants collected, from 18 species. The red imported fire ant was the most abundant species collected during the first year after planting with 52,648 individuals (45% of all individuals).
Accomplishments
Review Publications
Khambhati, V.H., Abbas, H.K., Sulyok, M., Tomaso-Peterson, M., Chen, J., Shier, W.T. 2023. Mellein: Production in culture by macrophomina phaseolina isolates from soybean plants exhibiting symptoms of charcoal rot and its role in pathology. Frontiers in Plant Science. 14-2023. https://doi.org/10.3389/fpls.2023.1105590.
Riddick, E.W., Wu, Z., Chen, J. 2023. Differential susceptibility of Coleomegilla maculata (Coleoptera: Coccinellidae) and Scymnus creperus (Coleoptera: Coccinellidae) larvae to aggression by Solenopsis invicta (Hymenoptera: Formicidae) workers. Insects. https://doi.org/10.3390/insects14040318.
Chen, J., Du, Y. 2022. Fire ants feed their nestmates with their own venom. Journal of Insect Physiology. 142:104437. https://doi.org/10.1016/j.jinsphys.2022.104437.
Kim, S., Cantrell, C.L., Avula, B., Chen, J., Schrader, K., Santo, S., Ali, A., Khan, I.A. 2022. Streptomyces distallicus, a potential microbial biolarvicide. Journal of Agricultural and Food Chemistry. https://pubs.acs.org/doi/10.1021/acs.jafc.2c03537.
