LaCrosse virus infection of mammalian BHK cells is highly cytopathic, whereas that of mosquito C6/36 cells is asymptomatic and persistent. When the individual mRNAs and their genome segments are followed in parallel infections, cytopathic effects were found to correlate with the rate of synthesis, but not the accumulation, of the viral RNAs. The change from the acute to the persistent phase of the infection in C6/36 cells was found to take place at 24 hr p.i., at which time genome and N protein synthesis was severely reduced, even though mRNA levels remained high. When the persistent infection was followed for 72 days, the total amounts of genomes and their relative proportions were found to fluctuate greatly, whereas mRNA levels were either severely reduced or undetectable. DI genomes could not be detected during this time. The self-limiting nature of the mosquito cell infection appears to be due the translational control of N protein synthesis.