Submitted to: Journal of Invertebrate Pathology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 5/26/2010
Publication Date: 6/1/2010
Citation: Allen, C., Briano, J.A., Varone, L., Oi, D.H., Valles, S.M. 2010. Exploitation of a high genomic mutation rate in Solenopsis invicta virus 1 to infer demographic information about its host, Solenopsis invicta. Journal of Invertebrate Pathology. 105(1):105-111. 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 approximately $6 billion in damage annually and can pose a serious threat to human health. Recently, a promising microbial control agent (Solenopsis invicta virus 1) of the red imported fire ant was discovered. Scientists at the Center for Medical, Agricultural and Veterinary Entomology in Gainesville, FL, and South American Biological Control Laboratory, Argentina, have exploited the high mutation rate of this virus to identify the sources of fire ant infestations in other parts of the world, specifically Taiwan. Source information is critical to understanding how the fire ants expand their range and for choosing the most optimal biological control agents. In addition, differences in gene structure were identified which may be linked to virulence of the virus. Studies examining the basic biology of this virus are necessary to determine and develop its usefulness as a microbial control agent against fire ants.
Technical Abstract: The RNA-dependent RNA polymerase (RdRp) region of Solenopsis invicta virus 1 (SINV-1) was sequenced from 47 infected colonies of S. invicta, S. richteri, S. geminata, and S. invicta/ richteri hybrids collected from across the USA, northern Argentina, and northern Taiwan in an attempt to infer demographic information about the recent S. invicta introduction into Taiwan by phylogenetic analysis. Nucleotide sequences were calculated to exhibit an overall identity of >90% between geographically-separated samples. A total of 171 nucleotide variable sites (representing 22.4% of the region amplified) were mapped across the SINV-1 RdRp alignment and no insertions or deletions were detected. Phylogenetic analysis at the nucleotide level revealed clustering of Argentinean sequences, distinct from the USA sequences. Moreover, the SINV-1 RdRp sequences derived from recently introduced populations of S. invicta from northern Taiwan resided within the multiple USA groupings implicating the USA as the source for the recent introduction of S. invicta into Taiwan. Examination of the amino acid alignment for the RdRp revealed sequence identity >98% with only 9 amino acid changes observed. Seven of these changes occurred in less than 4.3% of samples, while 2 (at positions 223 and 242) were featured prominently. Changes at positions 223 and 242 accounted for 36.2% and 34.0% of the samples, respectively. Two distinct groups were observed based on the amino acid residue at position 223, Threonine or Serine. In cases where this amino acid was a Threonine, 90% of these sequences possessed a corresponding Valine at position 242; only 10% of the Threonine223–containing sequences possessed an Isoleucine at the 242 position. Among the Serine223 group, 76% possessed an Isoleucine at position 242, while only 24% possessed a Valine. Thus, it appears that the Threonine223/Valine242 and Serine223/Isoleucine242 combinations are predominant phenotypes.