Location: Biological Control of Pests Research
2018 Annual Report
Objectives
Objective 1: Discover new efficacious natural products, including fire ant-specific pathogens, for Integrated Pest Management (IPM) of invasive ant species.
Sub-objective 1A: Evaluate naturally occurring toxins for invasive ant control.
Sub-objective 1B: Evaluate entomopathogenic agents for invasive ant control.
Objective 2: Determine gene function and utilize existing genomic resources to develop gene disruption approaches for mitigating the impact of invasive ants.
Sub-objective 2A: Perform database comparisons to identify candidate genes for disruption.
Sub-objective 2B: Functionally characterize specific candidate genes targeted for disruption.
Objective 3: Improve existing and design new biopesticide delivery systems as part of Integrated Pest Management (IPM) programs for invasive ant species.
Sub-objective 3A: Enhance the efficacy of biopesticides by improving adjuvants and synergists.
Approach
Current practice for controlling invasive pest ants depends heavily on synthetic insecticides, which have hazardous impacts beyond their intended uses. New safer and more sustainable technologies are needed to improve pest ant management. This project plan describes research to develop new products for managing invasive ants, particularly the imported fire ant, Solenopsis invicta, and the tawny crazy ant, Nylanderia fulva. This research will focus on 1) identifying new biopesticides, including naturally occurring toxins and biological control agents; 2) identifying and characterizing targets and methods for gene disruption; and 3) developing and improving delivery systems to maximize the efficacy of newly developed and existing biopesticides. This research will produce innovative products and methods for managing invasive pest ants.
Progress Report
A series of natural occurring compounds were evaluated for their toxicity against fire ants. Several selected compounds were used in developing fire ant mound treatment formulations. In field trials, formulations based on both hexyl and methyl benzoate showed significant efficacy against fire ants, particularly the hexyl benzoate based formulation that achieved 100% control 3 weeks after mound treatment. Due to its low mammalian and aquatic toxicity, hexyl benzoate is promising active ingredient for fire ant control. In order to understand their toxicology, the effect of hexyl benzoate and methyl benzoate on the activity of esterases, glutathione S transferase and acetylcholinesterase in fire ants were investigated.
In order to find new naturally occurring compounds for invasive ant control, evaluate naturally occurring toxins for invasive ant control, we continued our effort in searching for natural toxins from ants. A Juvenile hormone(JH) mimic was found in an ant species in collaboration with an ARS scientist in University, Mississippi. This Juvenile hormone mimic was purified. Its sublethal effect was evaluated on fire ants, such as its effect on reproduction, digging and brood care behavior. Our research also demonstrated that volatiles from a native ant species are potent acute toxins against fire ants. Most volatile components of this ant have not been identified. Bioassays on the contact and fumigation toxicities of ant extraction is ongoing.
Ant alarm pheromone and compounds that enhance ant locomotion can serve as synergists to contact toxicants by increasing ant’s contact with toxicants. Those compounds can be potentially used as synergists in fire ant mound treatment formulations. Fire ant alarm pheromone was tested as a synergist in this aspect. In addition to fire ants, fire ant alarm pheromone elicited strong Electroantennogram (EAG) response of many other insects, including four other ant species, honeybee, Begrada bug, lady beetle, housefly, small hive beetle, yellow fever mosquito, termite, bedbug, water hyacinth weevil, southern green sting bug and two aphids. The results strongly suggest that fire ant alarm signal may have an effect on widespread insect species. It may be a broad spectrum insect repellent.
In order to identify candidate genes for disruption, comparative transcript expression analysis was conducted on fire ants. Microbial content in larva/pupa transcriptomes was also investigated. Two ant viruses were discovered in the Mississippi Delta. One of these is the first report of a crazy ant virus found in a fire ant. Performed multiple reference-based assemblies of 6 sequenced (paired Illumina reads) samples of red imported fire ants to identify RNA viruses. Analyzed sequences and discovered three viruses, two of which were unique. Designed specific primers for PCR-based virus detection.
Mortality caused by indirect exposure to two entomopathogenic fungi, Metarhizium (M.) brunneum and Beauveria (B.) bassiana (GHA and NI8 strains) to the red imported fire ant workers was evaluated. Groups of 50 workers were placed in one side of dual-box arenas. The opposite side of the arenas was lined with filter paper squares previously sprayed with unformulated purified spores (106 spores/ml) suspended in 0.2% Ethal TDA 3, HLB 8 of the three fungal strains, or untreated filter paper squares as the control. Daily observations were done for 1 week to determine mortality. Dead ants from each treatment and control were collected, surface cleaned, and placed in PDA media and incubated at 27°C, 60% RH for 7 days to detect fungal growth. The presence of fungal growth in the dead ants confirmed that fungal spores infected workers while walking on the treated paper. In the M. brunneum and B. bassiana GHA treatments, 51.35 and 56.68% of the workers died, respectively, during days 1 and 2. However, only 9.47 and 35.96% of the mortality could be explained by fungal infection by M. brunneum and B. bassiana GHA, respectively. Most of the mortality observed in the B. bassiana NI8 treatment (84.48%) occurred later (between days 4–6) and most of this mortality occurring during day 4 (89.06%) could be explained by B. bassiana infection. Overall mortality was significantly higher in the B. bassiana NI8 treatment than the other two fungi tested and control. Preliminary field studies indicated that Beauveria bassiana NI8 is effective in controlling the red imported fire ant when incorporated into a bait formulation.
Accomplishments
Review Publications
Shi, O., Lu, L., Lei, Y., He, Y., Chen, J. 2017. Volatile compounds from the ghost ants, Tapinoma melanocephalum, and their electroantennogram and behavioral activities. Environmental Entomology. 46(6):1374-1980.
Rojas, M.G., Elliott, R.B., Morales Ramos, J.A. 2018. Mortality of Solenopsis invicta workers (Hymenoptera: Formicidae) after indirect exposure to unformulated spores of three entomopathogenic fungi. Journal of Insect Science. 18(3):1-8.
Feng, Y., Chen, J., Zhang, A. 2018. Commercially available natural benzyl esters and their synthetic analogs exhibit different toxicities against insect pests. Scientific Reports. https://doi.org/10.1038/s41598-018-26242-6.
Gundersen, D.E., Adrianos, S.L., Allen, M.L., Becnel, J.J., Chen, Y., Choi, M.Y., Estep, A., Evans, J.D., Garczynski, S.F., Geib, S.M., Ghosh, S.B., Handler, A.M., Hasegawa, D.K., Heerman, M.C., Hull, J.J., Hunter, W.B., Kaur, N., Li, J., Li, W., Ling, K., Nayduch, D., Oppert, B.S., Perera, O.P., Perkin, L.C., Sanscrainte, N.D., Sim, S.B., Sparks, M., Temeyer, K.B., Vander Meer, R.K., Wintermantel, W.M., James, R.R., Hackett, K.J., Coates, B.S. 2017. Arthropod genomics research in the United States Department of Agriculture-Agricultural Research Service: Applications of RNA interference and CRISPR gene editing technologies in pest control. Trends in Entomology. 13:109-137.
