Population density of Agonoscena pistaciae (Hemiptera: Psyllidae) and spatial distribution pattern of its nymphs on three pistachio varieties in Khorasan Razavi province

Common pistachio psylla, Agonoscena pistaciae, is a key pest of pistachio trees in Iran. Sampling was done from three pistachio orchards including Sefid, Akbari and Kale-Ghochi varieties. Sample units for nymphs and adults were leaf and a yellow sticky trap, respectively. The number of nymphs on leaf and adult the number captured by traps was recorded weekly. The densities of nymphs and adults were significantly affected by pistachio varieties. The spatial distribution pattern of A. pistaciae nymphs was determined by indices of variance to mean ratio and regression methods of Taylor and Iwao. Indices of variance to mean ratio showed that spatial distribution of common pistachio psyllid in 2015 on three pistachio varieties was a random distribution. In 2016 and pooled two years, on Sefid variety random distribution and on Akbari and Kalle-Ghuchi varieties aggregated distributions were indicated. The aggregation indices in Taylor's model and Iwao's patchiness regression on the three pistachio varieties and during two years were both significantly greater than one. The spatial distribution of nymphs at Taylor’s model on Sefid pistachio and aggregated on other varieties in 2015. In Iwao's patchiness regression, spatial distribution in 2015 and 2016 was random on Sefid variety and aggregate in other cases. However, the data obtained showed that Iwao's patchiness regression gave a better fitness with all data in comparison with Taylor's power law. The results can be used to improve the sampling program and implementation of pest management programs of this important pest.