Monitoring of susceptibility of different populations of pistachio psyllid Agonoscena pistaciae (Hem.: Psyllidae) to imidacloprid and chlorpyrifos in pistachio orchards

Frequent and extensive use of various pesticides to control of common pistachio psylla (Agonoscenapistaciae), as one of the most important pests of pistachio, has provided the possibility of reduced susceptibility of this pest to pesticides. In this study, the susceptibility of 13 populations of A. pistaciae collected from pistachio orchards at areas of Bardaskan, Khalil Abad and Feiz Abad were studied to imidaclopridand to chlorpyrifos using bioassay experiments by leaf disc dipping method and based on the discriminating dose. The bioassay results indicated that the LC50 values of imidacloprid and chlorpyrifos on the susceptible population were determined as 261.2 and 83.03 ppm, respectively. The bioassay with discriminating dose (i.e. LC90 of the susceptible population) showed that all of the tested populations were susceptible to chlorpyrifos. But there were significant differences in susceptibility to imidacloprid between different populations compared to the susceptible one. The highest mortality percentage applying the discriminating dose was obtained for Kondor- susceptible population and the lowest one was related to Jalal-Abad, Zaher Abad and Kondor- resistant populations. The biochemical assays with measuring the esterase activity demonstrated that one of the mechanisms reduce susceptibility was an increase of esterase activity; so that, the activity of the susceptible population was 2.5 times less than that of populations that had low sensitivity. Furthermore, zymogram analysis showed that all populations had 2 enzyme bonds that qualitatively differ in the case of non-sensitive populations compared to the susceptible one. Measurement of glutathione S-transferase activity also showed that this enzyme system was involved in the reduction of the susceptibility of common pistachio psylla to imidacloprid.