Queensland fruit fly virus, a probable member of the Picornaviridae

A picornavirus was isolated from various life stages of the Queensland fruit fly, Dacus tryoni. This virus, Queensland fruit fly virus (QFFV) has virions with a diameter of 30 nm and a sedimentation coefficient of 178 S. One third of the particles in preparations were empty capsids or natural top component (NTC) with a sedimentation coefficient of 95 S. The buoyant density (rho) of virions and NTC in CsCl was 1.34 and 1.30 g/ml respectively; small amounts of a dense component (rho = 1.45 g/ml) were also detected. The capsid contained three major protein species of molecular weight (mol.wt.) 41,700, 36,500, and 31,300, in approximately equimolar proportions. NTC contained three major species of mol. wt. 44,700, 41,700, and 31,300. The nucleic acid present only in the bottom component virions was RNA and comprised about 30% of the particle weight and had a mol. wt of 2.88 kd, contained a poly(A) tract, and had a base ratio: G = 20; A = 32; C = 15; U = 33. The mol. wt. of the virion was estimated to be approximately equal to 9.5 kd. When virions were heated at 56 degrees C and above, they converted into artificial top component (ATC), which had the same protein composition as the virion when analysed by SDS-PAGE. In immunodiffusion tests the virions and NTC were indistinguishable, but a minor difference in antigenicity was detected between the virions and ATC. Virions were stable between pH 3 and 9 inclusive, and between 5 and 7 in the presence of 0.14 M NaCl. Immunodiffusion tests showed that QFFV was serologically unrelated to a range of picornaviruses as well as an unclassified virus isolated from the Mediterranean fruit fly, Ceratitis capitata. The data show that QFFV is probably a member of the Picornaviridae, genus Enterovirus.