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

Solenopsis invicta virus 4 (SINV-4), a new polycipivirus, was characterized in the host in which it was discovered, Solenopsis invicta . SINV-4 was detected in the worker and larval stages of S. invicta , but not in pupae, male or female alates, or queens. The SINV-4 titer was highest in worker ants, with a mean of 1.14 × 10 7 ± 5.84 ×10 7 SINV-4 genome equivalents/ng RNA. 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 S. invicta collected in Argentina, SINV-4 was detected in 22% of 54 colonies surveyed from across the Formosa region. There did not appear to be any seasonality associated with the SINV-4 infection rate among S. invicta nests. SINV-4 was successfully transmitted to uninfected S. invicta colonies by feeding. Among three colonies of S. invicta inoculated with SINV-4, two retained the infection for up to 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, the plus genome strand of SINV-4 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 (minus) genome strand was only detected in S. invicta . SINV-4 infection did not impact 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 from that of 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 (287.7 ± 45.2 eggs laid/24 hours) and uninfected control colonies (193.0 ± 43.6 eggs laid/24 hours).