Rate of spread of PVYn by alate Myzus persicae (Sulzer) from infected to healthy plants under laboratory conditions

Alate green peach aphids, Myzus persicae (Sulzer), tested in a flight chamb er during their maiden flight period displayed behaviours ranging from repe ated trivial flights to settling on the plants. The interaction of alate ve ctor density and PVYn spread was dichotomous, virus spread was significantl y related to vector density in some trials but virus spread was nil or limi ted and not significantly dependent on vector density in others. The green peach aphid colony used in these experiments provided a mixture of active a nd highly active alate populations. Results suggest that inactive and activ e vectors came from the active and highly active alate populations, respect ively. Therefore, winged aphids within a species cannot all be attributed t he same vector efficiency unless known to originate from the same populatio n. At a 15% inoculum level the intercept for the regression model for the s pread of PVYn was 5.03% indicating that there is a significant probability of propagation at aphid densities as low as one. However, over the range of aphid densities tested, the rate of spread per aphid was low, 0.08%, sugge sting that reinfection of newly infected plants or movement interference be tween aphid vectors rapidly became important factors negatively affecting v irus spread. Although these results cannot be directly transferred to field conditions they provide confirmation that low M. persicae numbers can tran smit unacceptable levels of mosaic and that low inoculum levels are require d to decrease the risk of transmission by the small aphid numbers which can not be realistically controlled.