ニカメイチュウ被害茎密度の推定について

抄録

In the present paper, the data on the frequency distribution of infested stems per rice hill caused by the rice stem borer, Chilo suppressalis, were used. These data were collected from 41 different rice fields in Western Japan over several years. From these data the relation between the mean number of infested stems per rice hill and the proportion of infested units is obtained as shown in Fig. 1, abscissa showing density of infested stems (λ) and ordinate percentages of infested units (P). This relation opens the way to estimate λ by P.
If the frequency distribution of infested stems per unit is fully random, the proportion of infested units (P) is to be expected as follow,
P=1-e^-λ,
where λ is the mean number of infested stems per unit. In practice, P is usually shown somewhat underestimated, because of the departure from random distribution. The “negative binomial” often gives a good fit to the actual distribution of infested stems per unit. Thus, the above equation will be changed as follow,
P=1-e^-aλb,
where a and b are constant. Putting m=aλ^b, P can be transformed in to m, by using Table 1. Fitness of this equation can be examined by a lineality between logλ and logm. The empirical data well agree with this equation. (Fig. 2) By estimating the paramaters, a and b, the following formula was obtained.
P=1-e^{-0.487λ0.937}
Table 1 gives calculated values of λ to different percentages of P.
This method is intended to save work, because it is far easier to count the number of infested hills than to count infested stems per hill. Some factors affecting this method are discussed.