Seasonal activity and spatial distribution pattern of Eotetranychus frosti (Acari: Tetranychidae) in an unsprayed apple orchard of Kermanshah, Western Iran

Population density and spatial distribution pattern of Eotetranychus frosti (McGregor) was determined in an unsprayed apple orchard of Kermanshah, Western Iran, from 31st May till 7th November 2007. On each sample date 130 leaves were selected, with a relative variation of 4.31%. Different methods of indices of dispersion, regression models (Taylor and Iwao), Morisita’s index and Lloyd’s mean crowding to mean was used to determine the spatial distribution pattern of this mite. The mean population density of this mite per leaf was 2.079. The highest population density of E. frosti was in 9th August (4.938 per leaf). Index of dispersion (S2/m= 6.516), aggregation index (1/k= 2.653) and Lloyd’s mean crowding to mean (m*/m=3.653) showed an aggregated distribution for this species. The Taylorʹs power law and Iwaoʹs patchiness regression methods showed aggregated spatial distribution too. Some changes in spatial distribution pattern from aggregated to random were observed using Morisita’s index in different sampling dates. Three different coefficients of Taylor, Iwao and K were used to optimize the sample size for future studies. The lowest optimized sample size (34.70) was obtained by using the Taylorʹs coefficients. Spatial distribution parameters of E. frosti can be used to improve a sampling program of this mite in a framework of an integrated pest management system.