Density, spatial dispersion, and sequential sampling of Date Palm spider mite Oligonychus afrasiaticus on six Date Palm cultivars

Abstract

The Date Palm spider mite (DPSM), Oligonychus afrasiaticus (McGregor), is the most critical pest on Date Palm. We studied the standardization of the class-specific sampling method to define the appropriate unit and size and the population dispersion pattern of DPSM in its specific ecological niches and fitting of a Wald,s sequential sampling model on six Date Palm cultivars in five provinces. The sampling was repeated at seven days intervals from May to September. Finally, the dispersion pattern of DPSM in the Date Palm orchards was estimated using indices of mean crowding, Taylor’s Power Law, mass average index, patchiness, and Iwao. As DPSM had a clumped pattern, the first and second-type errors were considered equal to 0.1. The results showed that the means density of DPSM varied from 9.25 (Sayer cultivar) to 41.64 (Berhee cultivar) on 20 fruits. According to Taylor’s power law, the dispersion of this pest was clumped. Average Sample size decreased by increasing the population density of DPSM. By these results, The decreasing of operational curve slopes of sequential sampling models were different in the different Date Palm cultivars so that the slope was reduced to 0.5, 0.3, 0.3, 0.25, 0.1, and 0.1 for Pyaroom, Mazafati Rabi, Sayer Berhee and Kabakab cultivars, respectively. Proposed Wald,s sequential sampling model can be suggested for monitoring DPSM population on different Date Palm cultivars because it could drastically decrease sample size compared with the classical sampling model.