Spatial Distribution and Seasonal Activity of Panonychus ulmi (Acari: Tetranychidae) and Its Predator Zetzellia mali (Acari: Stigmaeidae) in Apple Orchards of Zanjan, Iran

Study of the spatial distribution of a pest and its natural enemies provides betterdecision tool for integrated pest management. the spatial distribution and seasonalactivity of panonychus ulmi (koch) and its predator zetzellia mali (ewing) were studied inan apple orchard in khoramdareh (zanjan province, iran) during 2007. the interaction(density dependence) between the prey and its predator was determined. for p. ulmi rv(relative variation) and reliable sample size were calculated with 25 percent variationfrom primary sampling at 18.8% and 59 leaves, respectively. the distribution pattern ofboth species was analyzed using nine statistical formulae: taylor’s power law, iwao’spatchiness regression, index of dispersion, morisita’s coefficient of dispersion, lloyd’smean crowding, david and moore's index, cole's index of dispersion, green's index andcoefficient of 'k' (coefficient of aggregation). the results indicated that the highestpopulation density of p. ulmi and z. mali were on 11 august (23.92 per leaf) and 11september (8.2 per leaf), respectively. the slopes of taylor's power law and iwao'spatchiness regression methods were 1.82 and 2.18 for prey and 1.39 and 1.92 for predator,respectively. these slopes had significant difference from one, indicating aggregatedspatial distribution in prey and predator. the index of dispersion (id) showed that thespatial distribution of p. ulmi in apple orchards was aggregated but it showed randomdistribution for z. mali. the morisita’s coefficient, lloyd’s mean crowding and green'sindex showed an aggregated distribution for both species. the regressions betweenpopulation densities of p. ulmi and z. mali indicated a density independent reaction ofpredator to the prey. the effect of temperature and humidity on the prey and predatorpopulations was estimated. spatial distribution parameters of the prey and predator canbe used in integrated pest management programs.