2024 Volume 2024 Issue 138 Pages 41-48
I evaluated a method for estimating the population density of phytoseiid mites infesting commercial tea fields in Shizuoka Prefecture. The method employs a beating technique, where tea canopies are beaten onto a B5 white board to dislodge and collect mites infesting the leaves. A significant positive correlation was found between the mean numbers of these mites collected using the beating method and the level of infestation on hedge leaves, i.e., the number of mites and the rate of infested tea leaves. The distribution pattern in the field was analyzed using the data obtained from the beating method. I observed that the basic aggregation degree (α) was -0.0242, and the aggregation coefficient (β) was 1.03, indicating a random distribution (Poisson distribution). Additionally, I calculated the number of samples required for the target accuracy of D＝0.1-0.3 based on these α and β values. When the mean number of phytoseiid mites was one per sample, the beating method was applied at 11 points per field to achieve a target accuracy of D＝0.3. Furthermore, I examined the method for estimating the mean number of these mites based on their presence-frequency ratio or maximum abundance estimated using the beating method. A nonlinear regression equation, y＝1 - exp (-0.987x0.985), was obtained for the relationship between their presence-frequency ratio (x) and mean value (y). Additionally, a linear regression equation, y＝0.408x, was obtained for the relationship between their maximum value (x) and mean value (y). In actual surveys, determining the presence-frequency ratios or maximum abundance of these mites in a preliminary survey, and then calculating the required number of samples based on the mean value estimated from these parameters, will enable a high-accuracy estimation of their population density.
