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

Authors: ALLEN, CLARE - Former ARS Employee; Valles, Steven

Submitted to: Florida Entomologist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/22/2015
Publication Date: 9/1/2015
Citation: Allen, C., Valles, S.M. 2015. Successful transcription but not translation or assembly of Solenopsis invicta virus 3 in a baculovirus-driven expression system. Florida Entomologist. 98(3):943-949.

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. Control of this pest is largely achieved by chemical insecticides. The virus, Solenopsis invicta virus 3, discovered by USDA-ARS scientists at the Center for Medical, Agricultural and Veterinary Entomology (CMAVE, Gainesville, FL), has been shown to be a promising potential control alternative to chemical insecticides. Laboratory tests by USDA scientists have demonstrated the virus’ effectiveness. Unfortunately, production of pure virus is limiting commercial development and field use of the virus. Scientists at CMAVE have attempted to use a baculovirus expression system to produce pure SINV-3 in quantity. Transcription of the virus was possible, but expression and assembly of the virus failed.

Technical Abstract: Solenopsis invicta virus 3 (SINV-3) is an unclassified positive stranded RNA virus whose characteristics are amenable for development as a microbial insecticide or as a classical biological control agent for the red imported fire ant, Solenopsis invicta. 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 which 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 three 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.