Infection Models for Pine Wilt Disease on the Basis of Vector Behaviors

ABSTRACT Pine wilt disease is caused by the pinewood nematode ( Bursaphelenchus xylophilus Steiner et Buhrer) and induces the quick death of susceptible pine trees. In Japan, adults of the Japanese pine sawyer ( Monochamus alternatus Hope) transmit the nematodes to healthy trees and oviposit on the disease‐killed trees, which will produce new beetle adults with the nematodes the following year. To analyze disease epidemics, the infection models were built on an assumption of a binomial, Poisson, or negative binomial distribution of beetle visits among trees. The beetle adult density could be replaced by the mean number of emerging adults per dead tree times the density of the previous‐year dead trees per unit of area. Thus, the models contained the densities of healthy and dead trees, the transmission coefficient, and a parameter whose inverse expressed the degree of aggregation of beetle visits. The models showed the stabilizing effect of highly aggregated beetle visits among trees on the incidence of pine wilt disease. In addition, those models successfully simulated the annual change in the dead tree density over 7–10 years for four Japanese red pine ( Pinus densiflora Sieb. et Zucc.) stands infested with the disease and estimated the density of surviving trees at the end of the epidemic. Great positive deviations of the annual transmission coefficient values from the overall value suggested the reduced effectiveness of control measures. Discussion was made on the application of the proposed infection models to other insect‐transmitted diseases of woody plants.