Vector feeding period variability in epidemiological models of persistent plant viruses

Plant viruses are transmitted from one host plant to another by vectors, fr equently phloem feeding insects. Persistent, circulative plant viruses are found in the phloem of the host plant and can be transmitted within a minim um period of minutes or hours by their insect vectors. The probability of v irus inoculation increases with the period of exposure of the host to the v ector. In mathematical models of plant virus disease epidemics it is freque ntly assumed that virus transmission is a simple bilinear process, i.e. is proportional to the abundance of hosts, vectors, and a constant 'contact ra te' parameter. Thus no account is taken of any minimum feeding period requi red for virus transmission or of how the vector feeding period duration aff ects the probability of transmission. A theoretical model was developed to evaluate these effects. The results of numerical simulation with two models , conventional and with variable feeding period, were compared. The convent ional model was adequate when the mean feeding period by a vector on a plan t (T) greater than or equal to the average feeding period required for one inoculation event to occur (alpha). Particularly in pathosystems where the vectors are relatively inefficient virus transmitters the situation T < alp ha can occur, leading to underestimation or overestimation of the inoculati on rate when variability is ignored. Genetic changes in host or vector, e.g . associated with a new host plant variety, which result in an increase in the variability of the vector feeding period could give rise to unexpected changes in disease dynamics. (C) 2000 Elsevier Science B.V. All rights rese rved.