Population Dynamic, the Spatial Distribution Pattern and Management of Ash Tree, Fraxinus rotundifolia psyllid Psyllopsis discrepans Flor (Hem., Psyllidae) in Kermanshah Province, Iran

Due to increasing air pollution, one of the ways to reduce pollution is to develop the green space, the urban parks, domestic gardens and streets marginal, including the ash trees, which play a vital role in supporting urban by its beauty and reducing air pollution. One of the convenient options to overshadow ash trees in their gardens. The jumping plant-louse, Psyllopsis discrepans is a sap-suckerpest which has highly host -specific and feed mainly on the young leaves and sprouts, is considered as important ash pests. Large populations of the pest cause the leaf curl gall and distort which result in leaf scar and less aesthetic appearance of ash canopy. The pest causes plant weakness by the toxic action of the saliva injected during their feeding process. The nymphal instar secreted honeydew which stimulates fungal growth on plant organs. There are a number of psyllid control methods which each of them has its own set of advantages and disadvantages. The objective of this work was to verify the population fluctuation and assessing the spatial distribution of P. discrepans, in ash tree, Fraxinus rotundifolia Mill (Oleaceae) and in order to develop the best psyllid control plan, it is important that to weigh out the most effective options to reduce the population of this pest, in Kermanshah, western region of Iran.
In this study the monitoring of P. discrepans population was carried out in urban areas of infested trees, using yellow adhesive traps with 50 m far from each other. Two sampling methods were took place the regular weekly from March 2014 to May 2015. nymphs tend to cling to the foliage when disturbed while the adults tend to jump and fly away. These differences in habit necessitated the use of two sampling techniques. The counts of eggs and nymphs were made by taking samples at each infested tree. The samples were placed individually in plastic bags and chilled in a refrigerator until they could be observed under a dissecting microscope and the counts made. Adult populations were sampled by yellow sticky traps. The counts obtained for the various life stage intervals are recorded. The population dynamics and spatial distribution models was calculated, using Taylor’s law and Iowa's model. For the winter and spring chemical pest control Acetamiprid insecticide and the winter oil (volk oil) were employed in a randomized complete block design with three treatments and four replications for the eggs control in 2014 in the green space. In the spring a combination of pesticides, acetamiprid and imidaclopriyd, was done in a randomized complete block design with six treatments and four replications were used for adults and nymphal stages control in 2015 at the faculty of agriculture, Razi University in Kermanshah green space.
The results show that P. discrepans has two generations per year. The spring generation occurs in early April, the summer generation appears from late of June to beginning of October. The insect overwinters as eggs that hatch in early spring. The Taylor’s law showed cumulative spatial distribution in both years and the Iowa's model showed randomized spatial distribution in 2014, but showed cumulative spatial distribution in 2015. The Iowa's model based on coefficients of determination obtained (R=0.996) compared to the Taylor’s law (R=0.992) had a higher correlation with the data used to fit the data better than the Taylor rule. The pest control methods tested to reduce pest population levels, during winter and spering, including chemical control, physical control and combination of them. The chemical control results by volk oil and acetamiprid in compared with the control (water) in winter showed that effect of volk oil spray was better than acetamiprid on mortality all of stages. The results for pest control in the spring showed that the combination of spray chemical, imidacloprid yellow sticky card trap to control this pest were more effective than the other treatments. The yellow sticky card trap supports Anthocoris sp. at the field condition, during chemical control program. In conclusion, the population dynamics of P. discrepans related to temperature and humidity. P. discrepan populations were found during month of the year, reaching their peak in May and September. Average and maximum temperatures showed a significant correlation with the psyllidae population fluctuation, affecting it positively. Heavy rain periods and low temperatures were not restricting, but they caused a reduction in population.