Spatial distribution and sampling plan for Tetranychus urticae (Acari: Tetranychidae) in bean crops

The two-spotted spider mite, Tetranychus urticaeKoch, is one of the most destructive bean pests in the central part of Iran. Spider mites feeding on bean leaves cause physiological changes in the plant, which coupled with favorable environmental conditions can lead to increased mite infestations. Significant yield loss can occur in the absence of pest monitoring and timely management. Monitoring for its occurrence and the population density is usually done by visual inspection and consequently demands much effort and time. Hence the objectives of this study were 1) to describe the sampling distribution pattern ofthis mite and 2) to develop a fixed-precision sequential sampling plan for density estimation. Population estimates were made by registering the number of all stages on 150 leaves of bean plantsfrom mid to the end of July of 2021. Taylor's power law (TPL)was used to analyze the spatial distribution of the pest (r2=0.849). Aggregation Indexes (b=1.239) were significantly greater than one, indicating the aggregation of T. urticae. We used TPL parameters to develop a sequential sampling plan at precision levels of 0.10 and 0.25 using Green's method. Fixed-precision sequential sampling plan could represent a suitable method for samplingT.urticae population in bean fields in the Varamin area, with the practical advantage of lower cost and time consumption than standard sampling plans. The use of this plan outside the Varamin area can be applicable.In conclusion, the sequential sampling plans determined in this study for mites can be incorporated into integrated pestmanagement programs in bean crops by making precise and quick decisions.