Abstract
In previous work, relative infectivities of extracts of leafhoppers were determined at intervals after their acquisition of wound-tumor virus by feeding on plants for 1 day. The infectivity time curve of the insect extracts increased for 30 days at 27° and then declined. In the present research the absolute concentrations of virions in such extracts were determined in the peak region of the above curve by a particle-counting technique. The absolute virus concentration also reached a peak at 30 days, and the close similarity of the relative and absolute curves permitted equating one with the other at the peak. This made it possible to convert curves of relative infectivities in the earlier work to curves of approximate absolute virus concentrations. Specifically, a curve has been derived relating the absolute concentration of wound tumor virus injected into leafhoppers to the concentration of virus soluble antigen which develops in them later. Also, a curve has been derived which shows the approximate average number of virions per infected leafhopper between day 6 and day 40 after acquisition of virus by feeding. At days 6, 30, and 40, the average number of extractable virions per infected leafhopper is approximately 10 6.6, 10 9.26, and 10 8.7, respectively. The minimum infective dose by injection of leafhoppers is about 10 2.6 virions.
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