Occurrence of the green rice leafhopper, Nephotettix cincticeps UHLER, in relation to spreading of the rice waika disease in field

Abstract

Field investigations on epidemic of the rice waika virus disease (RWV), semipersistent leafhopper-borne virus, and on outbreak of the viruliferous green rice leafhopper, Nephotettix cincticeps UHLER, were carried out by planting a diseased seedling as a inoculum in an experimental field at the time of rice transplanting. Viruliferous vectors appeared throughout rice growing period and, in general, viruliferous percentage of adults was slightly higher than that of nymphs. Percentage of viruliferous adult was at its highest in the 3rd generation in middle. August in plot A, transplanted on June 14, or the 4th generation in plot B, transplanted on June 21, as was 49.7% in plot A and 41.2% in plot B. Percentage of RWV infected hills reached more than 90% toward July 19 in plot A, 5 weeks after transplanting, or August 8 in plot B, 7 weeks after transplanting, although the infected hills increased gradually until July 4, when the nymphs firstly appeared in each plots. Consequently, it has been suggested that 2nd generation nymphs played an important role in the virus transmis-sion in field. The spreading of RWV infection in field was observed to be very progressive compared with the case of the rice dwarf disease, persistent leafhopper-borne virus, because the population density of RWV-viruliferous vector increased rapidly due to high transmissive efficiency of vector to the virus and existence of no apparent incubation period in the vector body. In spreading of RWV by vectors, 1st generation adults extended the infected hills in the range of 4 or 5 m, the maximum distnce was 8 m. Subsequently, 2nd generation nymphs transmitted to surrounding hills within 1 m from the affected hills.