Epidemiology of lettuce necrotic yellow virus in South Australia. I. Relationship between disease incidence and activity of Hyperomyzus lactucae L

Abstract

The seasonal incidence of lettuce necrotic yellows virus (LNYV) was investigated over a period of 19 months in lettuce crops at a site near Adelaide. Incidence was high in November and December 1965 and in May 1966 but was negligible in crops grown at other times. A constant association was observed between high disease incidence and increased migratory activity of Hyperomyzus lactucae. Peaks in the incidence of LNYV were observed 4-5 weeks after peak numbers of alate H. lactucae were trapped. Of the aphid species trapped at this site, it appears that H. Iactucae was the sole important vector of LNYV. Comparatively large numbers of alate H. lactucae were trapped only when mean weekly temperatures were in the range 60-72¦F. It is suggested that meteorological data could be used in conjunction with observations of aphid populations to determine periods when spread of LNYV is likely.