Successful transcription but not translation or assembly of Solenopsis invicta virus 3 in a baculovirus-driven expression system

Solenopsis invicta virus 3 (SINV-3) is an unclassified positive stranded RNA virus whose characteristics are amenable to development as a microbial insecticide or as a classical biological control agent for the red imported fire ant, Solenopsis invicta Buren (Hymenoptera: Formicidae). Bait formulations containing SINV-3 have been produced and were used successfully to transmit the infection and cause significant mortality to fire ant colonies in the laboratory. Unfortunately, there is no available means of propagating infectious SINV-3 particles in vitro, and this has hampered its evaluation and development as a microbial insecticide. In this study, we attempted to utilize a baculovirus expression system as reported by others to produce SINV-3 infectious particles in quantity. A full-length copy of the SINV-3 genome was assembled successfully from 3 overlapping fragments, and a heterologous bacmid-SINV-3 vector (BAC_SINV-3) was produced. The insect cell line Sf21 was transfected with purified high-molecular weight BAC_SINV-3 and supported production of baculovirus expressing full-length SINV-3 transcripts. Despite successful transcription of the SINV-3 genome, evidence that translation was occurring could not be produced. Western analyses for the SINV-3 VP-2 capsid protein were consistently negative.