Location: Biological Control of Pests Research
2020 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
This project replaced project #6066-22320-009-00D, "Products for Invasive Ant Control." Refer to project #6066-22320-009-00D for additional information.
Chemical communication is critical for the integrity and survival of fire ant colonies. Understanding chemical communication is important in developing new methods and approaches for managing fire ants. Olfactory neuron responses of fire ants to 62 compounds were investigated using single sensillum recording. These compounds include terpene, terpenoids, pyrazine, pyridine, ketone, aldehyde, alcohol, acid, aliphatic and aromatic acetate, benzoate, benzyl ester, etc. The multiple olfactory receptor neurons in workers and female alates elicited same responses to 38 compounds. Workers showed greater responses to 18 compounds and female alates showed greater responses only to 6 compounds. A comprehensive map of olfactory response to general odorants was established in fire ants, which is useful for searching for new attractants or repellents for fire ant control (Sub-objective 1B: Discover naturally occurring and synthetic compounds as behavior-modification agents for invasive ant control).
Electroantennographic response of fire ants to 26 new acetate esters was investigated. A large diversity of response tuning and behavioral responses were found. For linear alkyl acetate esters, the response was clearly affected by the carbon chain length of the alkyl group. Linear alkyl acetates with 5-7 carbon chain length of the alkyl group elicited significant response, whereas those with shorter (C1 to C4) or longer (C8 to C12) carbon chain lengths did not. Different substitutions also exhibited large variety of electroantennographic and behavioral responses. By exploring the olfactory and behavioral response of fire ants to structurally different acetate esters, two fire ant attractants and two potent repellents were identified. These compounds may be useful in developing new products for fire ant management (Sub-objective 1B: Discover naturally occurring and synthetic compounds as behavior-modification agents for invasive ant control).
Digging behavior is critical to the survival of the fire ant colonies since digging is one of fundamental behaviors involved in building nest and foraging tunnels. The volume of a fire ant nest is directly proportional to the colony size. In other words, fire ants are able to assess the volume of their nest and precisely regulate their digging behavior. How fire ant achieve this is kept unknown. Digging behavior of fire ants was studied using sand as a digging substrate. When the group size is small, grouped ants often had higher digging amounts per individual than an ant in solitary, indicating that social facilitation occurred among ants. However, while group size increased further, the digging amount per ant decreased, indicating digging inhibition took place. Ants preferentially dug the sand treated with worker body extracts over the untreated sand and more ants were found in the treatment at the end of experiment. The body extract also significantly increased the percentage of ants that showed digging effort. These results indicate that chemical cues may play a role in social facilitation of digging behavior in red imported fire ants; however, this data can’t explain the social inhibition observed in this experiment. In order to understand how fire ants regulate their nest volume, the mechanisms behind the observed social facilitation, social inhibition and their transition must be elucidated (Sub-objective 1B: Discover naturally occurring and synthetic compounds as behavior-modification agents for invasive ant control).
Assemblies using RNA fastq data (A01-Z03) were re-analyzed using ArrayStar. Identified a target gene expected to produce lethal knockdown phenotype. The gene has been tested in other organisms and was cross-referenced to the RNA samples used for differential expression. Newly submitted SRRs were downloaded and assembled with LaserGene SeqMan NGen 17 for additional cross-referencing (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).
Accomplishments
Review Publications
Allen, M.L. 2020. Near-complete genome sequences of new strains of Nylanderia Fulva virus 1 from Solenopsis invicta. Microbiology Resource Announcements. 9:e00798-19.
Du, Y., Grodowitz, M.J., Chen, J. 2020. Insecticidal and enzyme inhibitory activities of Isothiocyanates against Red Imported Fire ants, Solenopsis invicta. Biomolecules EISSN 2218-273X. 10(5):716.
Du, Y., Grodowitz, M.J., Chen, J. 2019. Electrophysiological responses of eighteen species of insects to fire ant alarm pheromone. Insects. 10:1-15.
Chen, J., Wang, L., Zhao, J. 2019. Pyridine alkaloids in the venom of imported fire ants. Journal of Agricultural and Food Chemistry. 41:11388-11395.
Chen, J. 2020. Evidence of social facilitation and inhibition in digging behavior of red imported fire ants, Solenopsis invicta. Insect Science. https://doi.org/10.1111/1744-7917.12781.
