Descriptive models for the system of the natural spread of infection of rice dwarf virus (RDV) by the green rice leafhopper, Nephotettix cincticeps Uhler (Hemiptera: Deltocephalidae)

Summary Seasonal changes in the densities of eggs and of 1st instar nymphs of N. cincticeps , a vector of the rice dwarf virus (RDV) and those in the proportion of virus‐infected rice hills were examined by regular field censuses during the period of 1964–69 at two localities in Kochi, Nangoku and Ino. The proportion of virus‐infected insects in the vector population was measured by the serological test. Mean fecundity of adult females of N. cincticeps in different generations was assessed by the method proposed by Hokyo and Kiritani (1968) in 1966 and 1967. Using observed variables as mentioned above, two mathematical models were built up for the system of the natural spread of infection of RDV. Submodels describing generation‐to‐generation changes in densities of eggs, 1st instar nymphs and leafhopper adults were involved in both Models 1 and 2 . In Model 1 , the proportion ( P ) of infected insects in the vector population was assumed to be determined directly by the amount ( I v ) of infected rice plants in the field. In Model 2 , instead of relating P directly to I v , P was related to the acquisition rate ( W ) of RDV by the insects and to the effect of RDV ( αr ) on fecundity and survival of infected insects. Then, W was related to I v . The estimates of P by these models fitted well to the observed values for 1st to 3rd generations but a great deviation was noted in 4th and 5th generations. For the percentage of infected rice hills, both models gave relatively good estimates in the early planted rice, though they gave overestimated values in the late planted rice.