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Viruses as Biocontrol Agents
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Electron micrograph of fire ant virus (bar represents 100nm)Scientists in the Imported Fire Ant and Household Insects Research Unit have discovered a virus infecting the red imported fire ant, Solenopsis invicta.  This is the first virus shown to infect fire ants.  The 8,026 nucleotide, polyadenylated, RNA genome was sequenced completely (Figure at bottom, GenBank Accession Number AY634314).  It encodes two large open reading frames (ORF1 and ORF2), flanked and separated by 27, 223, and 171 nucleotide untranslated regions, respectively.  The predicted amino acid sequence of the 5' proximal ORF1 (nucleotides 28 to 4,218) exhibited significant identity and possessed consensus sequences characteristic of the helicase, cysteine protease, and RNA-dependent RNA polymerase sequence motifs from picornaviruses, picorna-like viruses, comoviruses, caliciviruses, and sequiviruses.  The predicted amino sequence of the 3' proximal ORF2 (nucleotides 4390 to 7803) showed similarity to structural proteins in the Dicistroviridae, especially the acute bee paralysis virus.  Electron microscopic examination of negatively stained samples from virus-infected fire ants revealed isometric particles with a diameter of 31 nm (Figure at top - bar represents 100nm), consistent with Dicistroviridae.  A survey for the fire ant virus from areas around Florida revealed a pattern of fairly widespread distribution.  Among 168 nests surveyed, 22.9% were infected.  The virus was found to infect all fire ant caste members and developmental stages, including eggs, early (1st-2nd) and late (3rd-4th) instars, worker pupae, workers, sexual pupae, alates (females and males), and queens.  The virus, tentatively named Solenopsis invicta virus (SINV-1), appears to belong to the picorna-like viruses.  Preliminary experiments indicated that the virus may cause slow brood death within the colony.  Investigations are currently underway to evaluate the potential for SINV-1 in fire ant control.

Schematic diagram of the fire ant virus genome and cloning strategy