Influence of temperature on the pathogenicity of Solenopsis invicta virus 3

Authors: Valles, Steven; PORTER, SANFORD - Retired ARS Employee

Submitted to: Journal of Invertebrate Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/16/2019
Publication Date: 7/17/2019
Citation: Valles, S.M., Porter, S.D. 2019. Influence of temperature on the pathogenicity of Solenopsis invicta virus 3. Journal of Invertebrate Pathology. 166:107217. https://doi.org/10.1016/j.jip.2019.107217.
DOI: https://doi.org/10.1016/j.jip.2019.107217

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. Solenopsis invicta virus 3 can plan an important role in providing sustainable and natural control of fire ants in the U.S. Scientists at the USDA-ARS, Center for Medical, Agricultural and Veterinary Entomology, Gainesville, Florida, investigated temperature-dependent prevalence of the virus in U.S. populations. They found that the virus is more prevalent during cooler times of the year and that virus replication and assembly was correspondingly more effective at lower temperatures. These results are important to ensure successful release of the virus as a control agent.

Technical Abstract: Field evaluations assessing the prevalence of Solenopsis invicta virus 3 (SINV-3) have shown that the virus exhibits a distinct seasonal phenology in the host, Solenopsis invicta, that is negatively correlated with warmer temperatures. Active SINV-3 infections were established in Solenopsis invicta colonies, which were subsequently maintained at 19.1, 22.2, 25.5, 27.7, and 29.3 °C. Brood ratings declined in all SINV-3-treated colonies regardless of temperature over the initial 30 days. However, brood ratings in colonies held at 29.3 °C began increasing in the next 40 days until they were statistically equivalent to ratings for untreated control colonies. Meanwhile, brood rating continued to decline in colonies held at 19.1, 22.2, 25.5, and 27.7 °C for the duration of the test (81 days). By the end of the test, these colonies were in poor health as indicated by brood ratings in the 1 to 1.5 range. Conversely, the mean brood rating for colonies held at 29.3 °C increased to above 3, indicating vigorous growth. Worker ants from SINV-3-treated colonies maintained at 19.1, 22.2, and 25.5 °C showed strong production of the VP2 capsid protein by Western blotting; 100% of the colonies sampled (n = 3) showed production of VP2. However, VP2 was detected in only 33% of colonies maintained at 27.7 °C, and the VP2 response was nearly undetectable in all colonies maintained at 29.3 °C. These results indicate that virus assembly does not appear to be occurring efficiently at the higher temperatures. Also, the quantity of SINV-3 detected in queens was significantly lower in those maintained at 29.3 °C compared with the lower temperature treatments. These results indicate that warm summer temperatures combined with fire ant thermoregulatory behavior and perhaps behavioral fevers may explain the low prevalence of SINV-3 in fire ant colonies during the summer.