Field evaluation of Solenopsis invicta virus 3 against its host Solenopsis invicta

Authors: Valles, Steven; Oi, David; WEEKS, JR, RONALD - Animal And Plant Health Inspection Service (APHIS); ADDESSO, KARLA - Tennessee State University; OLIVER, JASON - Tennessee State University

Submitted to: Journal of Invertebrate Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/24/2022
Publication Date: 4/29/2022
Citation: 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.
DOI: https://doi.org/10.1016/j.jip.2022.107767

Interpretive Summary: The red imported fire ant was introduced into the United States in the 1930s and currently infests about 300 million acres. It is estimated to cause $6 billion in annual economic losses to livestock and agricultural production and poses a serious threat to human health. Biological control is widely considered the most sustainable method of controlling the fire ant over its entire range. The virus, Solenopsis invicta virus 3, discovered by USDA-ARS scientists at the Center for Medical, Agricultural and Veterinary Entomology (CMAVE, Gainesville, FL), is a specific natural control agent against fire ants. Field inoculations of fire ant nests with the virus were conducted in Florida and caused reductions in the size and number of fire ant nests, as well as persistence and spread of the virus to adjacent uninoculated colonies. The fire ant virus provides an additional natural control agent against the ant with an advantage over traditional insecticides of no known detrimental ecological impacts, host specificity, and sustainability.

Technical Abstract: Viruses have been used successfully as biocontrol agents against several insect pests but not ants. Laboratory tests have shown that Solenopsis invicta virus 3 (SINV-3) may be an effective natural control agent against its host, the red imported fire ant (Solenopsis invicta Buren). In this first field trial, SINV-3 was released into 12 active S. invicta nests within a 0.088-hectare area in Florida and the impact on the ants monitored. SINV-3 was successfully transmitted, established, and multiplied within treated colonies reaching a maximum of 8.71 × 108 ± 8.26 × 108 SINV-3 genome equivalents/worker ant 77 days after inoculation. SINV-3 was not detected in any of the nests in the control group. A 7-fold decrease in nests was observed in the SINV-3-treated group compared with the untreated control; 1.75 ±0.5 S. invicta nests were eliminated from the SINV-3-treated plots compared with 0.25 ±0.5 nests in the control plots. A correspondingly significant decrease in S. invicta nest size also was observed over the course of the evaluation. Based on the nest rating scale, nest size among those treated with SINV-3 decreased from 3.92 ±1.24 on day 0 to 1.67 ±2.06 on day 77, which represents a 57.4% decrease in size. Conversely, the nest rating for the control group increased 9.3%, from 4.42 ±1.24 on day 0 to 4.83 ±2.12 on day 77. A follow-up survey of SINV-3-treated and -untreated plots conducted 9 months after initial treatment revealed that fire ant populations rebounded, but at a different rate. A total of 11 and 19 nests were detected in the SINV-3-treated and -untreated areas, respectively. SINV-3 was still detected in the treated area 1.8 years after the initial virus treatment and the virus had spread into the adjacent control plot.