Characterization of Solenopsis invicta virus 4, a polycipivirus infecting the red imported fire ant, Solenopsis invicta

Authors: Valles, Steven; Oi, David; OLIVER, JASON - Tennessee State University; BECNEL, JAMES - Retired ARS Employee

Submitted to: Archives of Virology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/26/2022
Publication Date: 9/13/2022
Citation: Valles, S.M., Oi, D.H., Oliver, J.B., Becnel, J.J. 2022. Characterization of Solenopsis invicta virus 4, a polycipivirus infecting the red imported fire ant, Solenopsis invicta. Archives of Virology. https://doi.org/10.1007/s00705-022-05587-4.
DOI: https://doi.org/10.1007/s00705-022-05587-4

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 $8 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. To use biocontrol to control fire ants, USDA-ARS scientists at the Center for Medical, Agricultural and Veterinary Entomology (Gainesville, FL) and Tennessee State University have discovered and characterized a new virus infecting the red imported fire ant. This study shows that the red imported fire ant does serve as host for SINV-4, but that overt symptoms of infection were not detected. However, subtle impacts not evaluated may occur and contribute to the overall control of imported fire ants in the U.S.

Technical Abstract: Solenopsis invicta virus 4 (SINV-4), a new polycipivirus, was characterized in the host from which it was discovered, Solenopsis invicta. SINV-4 was detected in worker and larval stages of S. invicta, but not pupae, male or female alates, or queens. The SINV-4 titer was highest in worker ants with a mean of 1.14 x 107 SINV-4 genome equivalents/ng RNA. The intra-colonial infection rate was also higher in workers (78.3%) than in the larvae (56.7%). Electron microscopic examination of negatively stained samples from particles purified from SINV-4-infected fire ant workers revealed isometric particles with a mean diameter of 47.3 ±1.4 nm. The mean inter-colony SINV-4 infection rate among S. invicta worker ants was 45.8 ±38.6 in Alachua county Florida. In Argentinean-collected S. invicta, SINV-4 was detected in 22% of 54 colonies surveyed from across the Formosa region. There did not appear to be a seasonal phenology associated with the SINV-4 infection rate among S. invicta nests. SINV-4 was successfully transmitted to uninfected S. invicta colonies by feeding. Among 3 colonies of S. invicta inoculated with SINV-4, two retained the infection for up 72 days. The replicative genome strand of SINV-4 was detected in 18% (n = 11) of SINV-4-infected S. invicta colonies. Among 33 ant species examined, SINV-4 (plus genome strand) also was detected in undetermined species of Dorymyrmex and Pheidole, Cyphomyrmex rimosus, Monomorium pharaonis, Pheidole obscurithorax, Solenopsis geminata, Solenopsis richteri, Solenopsis xyloni, and Solenopsis invicta. However, the replicative genome strand was only detected in S. invicta. SINV-4 infection did not have an impact on brood production or queen fecundity in S. invicta. The mean brood rating (63.3% ±8.8) after 31 days for SINV-4-infected colonies was not statistically different with -uninfected colonies (48.3 ±25.5). At the end of the 31-day test period, mean egg production was not significantly different between SINV-4-infected S. invicta colonies (193 ±45.2 eggs laid/24 hours) and -uninfected control colonies (193.0 ±43.6 eggs laid/24 hours).