Submitted to: Journal of Invertebrate Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/18/2007
Publication Date: 4/29/2007
Citation: Hashimoto, Y., Valles, S.M. 2007. Solenopsis invicta virus-1 tissue tropism and intracolony infection rate in the red imported fire ant: A quantitative PCR-based study. Journal of Invertebrate Pathology. 96(2):156-161. 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 significant economic losses in livestock and agricultural production and poses a serious threat to human health. USDA-ARS scientists at the Center for Medical, Agricultural and Veterinary Entomology (Gainesville, FL) have determined the tissue specificity, and intra-colony infection rate of the first virus discovered in the red imported fire ant. A hypothetical mode of transmission for the virus was also proposed based on the data acquired. These tests were crucial requirements for the potential development of the virus for use in fire ant control programs.
Technical Abstract: Quantitative real-time PCR was employed to measure the Solenopsis invicta virus 1 (SINV-1) load in tissues, individuals, and among colonies of the red imported fire ant, Solenopsis invicta Buren. Among tissues examined from SINV-1-infected adults and larvae, the alimentary canal (specifically the midgut) consistently had the highest number of SINV-1 genome copies (91.1 and 99.9 %, respectively). Negative staining of a supernatant of the gut homogenate demonstrated the presence of spherical virus particles with a diameter of 30 – 35 nm, consistent with SINV-1. The number of SINV-1 genome copies in infected larvae and workers from the same queenright colonies were similar to each other. In other words, the infection rate was consistent among both developmental stages. No significant differences were observed in SINV-1 genome copy number among infected colonies sampled during the winter and summer. Although the SINV-1 infection rate of summer-collected mounds was previously shown to be six-times higher than winter-collected mounds, the intra-colony infection rate appears to be unaffected by season. Perhaps less inter-mound interaction during the winter months among S. invicta restricts spread of the virus. A positive correlation between intra-colony infection rate and mean SINV-1 genome copy number per ant was also observed. Based on these results, it is likely that SINV-1 replicates in gut epithelia of S. invicta and virus is shed into the gut lumen where it may be transmitted to nestmates by trophallaxis.