Transmission of Cabbage Viruses A and B by the Cabbage Aphid and the Green Peach Aphid1

Abstract

Experiments were conducted to determine the modes of transmission of cabbage viruses A and B (CVA and CVB, respectively) by the green peach aphid, Myzus persicae (Sulzer), and the cabbage aphid, Brevicoryne brassicae (L.). Experiments using varying times of acquisition feeding and virus retention showed that both aphids transmitted CVA nonpersistently. M. persicae transmitted CVB similarly. B. brassicae transmitted CVB semipersistently. Transmission was efficient after long acquisition feeds. Plotting per cent transmission against acquisition time resulted in a bimodal curve with peaks around 5 minutes and 5 hours. It was hypothesized that B. brassicae transmitted CVE nonpersistently after short acquisition feeds and persistently after long feeds. Further evidence for the hypothesis was obtained from retention and serial transmission tests using either short or long acquisition feeds corresponding to the peaks in the bimodal curves. B. brassicae retained CVB longer after a long acquisition feed than after a short feed. Formaldehyde (0.25%) applied to viruliferous feeding cabbage aphids in solution through a membrane or directly to exposed stylets was used to inactivate CVB. The chemical in most instances prevented transmission by aphids given short (1 to 2 minutes) acquisition feeds. Using acquisition periods of 4 hours to 2 days, much less reduction of transmission resulted regardless of length of stylets treated, It was concluded that during short acquisition feeds, only the tips of sty lets were involved in CVB transmission. After long acquisition feeds, the transmissible virus apparently was not on the stylets or was protected in some way from virus inactivators. This conclusion lends further evidence to the hypothesis of bimodal transmission.