Cohen, S., The Volcani Institute, Agricultural Research Virus Laboratory, Bet Dagan, Israel

Studies were carried out on the effects in whiteflies of a possible antiviral factor apparently related to the phenomenon of periodic acquisition and termed "periodic acquisition related factor" (PARF). The acquisition efficiency (i.e., the percentage of individuals that actually transmitted the virus, out of the total number of individuals employed in the trial) of insects allowed to acquire tomato yellow leaf curl virus (TYLCV) immediately after taking in PARF was significantly less than that of control insects. Viruliferous whiteflies which had ingested PARF transmitted with lower efficiencies beginning at about 11 days after PARF uptake. This suggested that persistence of TYLCV in the insect's body might be reduced. PARF was not detected in whitefly females immediately after a 24-hour acquisition feeding, but was found 24 hours later. These and other results have a bearing on the stage(s) in virus infection at which PARF acts. © 1969.