Spatial distribution of grape leafhopper, Arboridia kermanshah (Hemiptera: Cicadellidae) immature stages, in vineyards of Kermanshah County

Grape leafhopper, Arboridia kermanshah (Hemiptera: Cicadellidae) is one of the important pests of grapevine in Iran. In this research, the spatial distribution of A. kermanshah immature stages was investigated in a vineyard of the Kermanshah region, during 2017 and 2018. Grape leaf selected as sampling unit and sampling process carried out every week. The spatial distribution of eggs and immature stages of this pest calculated using: Index of dispersion, Morisita, Lloyd’s mean crowding index, Iwao’s patchiness regression and Taylor’s power law Indexes. Most used methods revealed an aggregated spatial distribution for the pest (b>1). According to the Iwao’s method in first sampling year, regression for 4th and 5th nymphal instars, was not significant (P-value>0.05). In Taylor method for both sampling years and Iwao’s method for second sampling year, distribution calculated random for 4th and 5th nymphal stages. Also, using the Morisita’s index in both sampling seasons and most (10) sampling dates, for the 4th and 5th nymphal stages, random distribution calculated. In both sampling seasons, Taylor’s power law method found to be more accurate than other methods in determination of the spatial distribution for this pest. Additionally, the lowest optimum sample sizes calculated using Taylor’s coefficients that were more affordable in comparison with other methods. Knowledge of the spatial distribution of this pest can be useful in designation of suitable sampling programs. Estimation of optimum sample sizes can also be useful in decreasing of sampling costs in both research and management programs.