A STOCHASTIC SIMULATION-MODEL OF EPIDEMICS OF ARTHROPOD-VECTORED PLANT-VIRUSES

A generalized theoretical model was developed of the spread of a virus from a single source plant in a small field. Input parameters include probabilities of virus acquisition and inoculation, lengths of latent periods in the plant and vector, length of the vector infectious period, number of vectors per plant, and the amount of vector movement. Decisions about acquisition, inoculation, and vector movement are made on the basis of the values of pseudorandomly selected numbers. Output includes numbers of viruliferous vectors and positions of infected plants at each iteration. Simulation runs were performed for viruses with four generalized types of vector transmission: nonpersistent, semipersistent, circulative, and propagative. Model predictions were generally consistent with expected natural spread. Results of simulation runs illustrated the great effects that the amount of vector movement can have on disease dynamics and spatial distribution, particularly for diseases transmitted in a nonpersistent manner. The model will be difficult to fully validate; however, it provides a logically rigorous way of integrating knowledge about the many processes that affect virus disease epidemics and may be useful in the development of methods of analysis and in the development of less complex models.