Drosophila Sigma Virus

Sigma virus is a rhabdovirus which infects the fruitfly Drosophila. An important step in the understanding of sigma virus transmission was the discovery of a sigma virus mutant which does not permit the transmission of the agent to progeny of inoculated females, or females infected by the paternal gamete. The paralysis of sigma virus infected flies is specifically induced by CO₂ and no other gas. Infectious sigma virus is assayed by the end point dilution method using the induction of CO₂ sensitivity in susceptible flies as the test for the presence of virus. Cloning of sigma virus can be achieved by injecting flies at the end point dilution of a virus suspension such that 10% or less of the flies in a batch become CO₂ sensitive. One parameter in the study of sigma virus which can be exploited experimentally is the incubation time that precedes the appearance of CO₂ sensitivity in inoculated flies.