Dose response of red imported fire ant colonies treated with Solenopsis invicta virus 3

Authors: Valles, Steven; Porter, Sanford

Submitted to: Archives of Virology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/30/2015
Publication Date: 7/11/2015
Citation: Valles, S.M., Porter, S.D. 2015. Dose response of red imported fire ant colonies treated with Solenopsis invicta virus 3. Archives of Virology. doi: 10.1007/s00705-015-2520-1.

Interpretive Summary: The red imported fire ant was introduced into the United States in the 1930s and currently infests about 300 million acres. It causes economic losses that exceed 6 billion dollars annually in the United States and poses a threat to human health. USDA-ARS scientists at the Center for Medical, Agricultural and Veterinary Entomology (Gainesville, FL) have conducted dose response bait tests with the fire ant virus, Solenopsis invicta 3 (or SINV-3). The virus is being developed as a biopesticide as an alternative control method to chemical insecticides. SINV-3 was shown to be an effective control agent against fire ants in the laboratory when used in bait form. The study establishes an effective dose necessary for using the virus as a biopesticide and as a classical biological control agent. These results advance development of SINV-3 as a control agent for fire ants.

Technical Abstract: Baiting tests were conducted to evaluate the effect of increasing Solenopsis invicta virus 3 (SINV-3) doses on fire ant colonies. Actively growing, early stage, fire ant (Solenopsis invicta) laboratory colonies were pulse-exposed to six concentrations of SINV-3 in a 10% sucrose bait and monitored regularly for two months. SINV-3 concentration had a significant effect on colony health; significant differences in brood rating (proportion of brood to worker ants) were observed at 19, 26, 34, 45, and 60 days after virus exposure. Brood rating began to depart from the control group at 19 days for the 109 concentration and 26 days for the 107 concentration. At 60 days, brood rating was significantly lower in colonies treated with 109, 107, and 105 SINV-3 concentrations. The intermediate concentration, 105, appeared to cause a chronic, low-level infection with one colony (of nine exposed) showing replicating virus. Newly synthesized virus was not detected in fire ant colonies treated at the101 concentration indicating that active infections failed to establish at this concentration. The highest bait concentration chosen, 109, appeared most effective from a control aspect; mean colony brood rating at this concentration (1.1 ±0.9 at the 60 day time point) indicated poor colony health with minimal brood production. No clear relationship was observed between the quantity of plus genome strand detected and brood rating. Conversely, there was a strong relationship between the presence of the replicative genome strand and brood rating, which may serve as a predictor of disease severity. Recommendations for field treatment levels to control fire ants with SINV-3 are discussed.