Abstract
The age-related changes in the number of Bursaphelenchus mucronatus within its vector, adult Monochamus saltuarius, and an effect of B. mucronatus on the vector life span were investigated. Forty-three vectors were reared individually in containers under outdoor conditions. Pine twigs were supplied as food, and were renewed at five-day intervals. The number of nematodes carried by a vector continued to decrease as the vector aged. When a vector had carried 1, 000 or more nematodes at emergence, a rapid decrease was observed during a period between the 15th and 40th days after the emergence. It was observed earlier for some vectors carrying less than 1, 000 nematodes. The life span of the vectors ranged from 1 to 118 days. The life span was not affected by the number of nematodes carried, although there was an insignificant, negative correlation between them. B. mucronatus, which is avirulent against pine trees, usually has a low density of susceptible pine hosts in the forest because it can reproduce itself only in declining and newly killed trees. High transmission efficiency is necessary for the pathogen to persist at low host density. Effective transmission of B. mucronatus occurs after reproductive maturation of the vector. Thus, the absence of ill effect of B. mucronatus on vector longevity plays an important role in keeping transmission efficiency high.
