Spatial distribution of Thiacidas postica Walker (Lepidoptera: Noctuidae) larvae on Ziziphus spina-christi in Bushehr region

    The spatial distribution pattern of pests can be useful in planning and performing the integrated pest management.  The Konar moth, Thiacidas postica Walker (Lepidoptera: Noctuidae), is a defoliator of Konar (Ziziphus spina-christi), in south of Iran especially Bushehr, Hormozgan and Khuzestan provinces. The Larva is defoliator of Ziziphus spp. Extension of Konar cultivation in south of Iran as an economic orchards caused complete studies on some important pests. The spatial distribution of T. postica fifth instar larvae was studied in field conditions on the Ziziphus spp. during 2006-2008. A 50 cm of branches of each Konar tree was selected as sampling units. With a primary sampling sample size was determined as 40. In this research, the spatial distribution pattern of fifth instar larvae of T. postica using regression models (Taylor’s power law and Iwao’s patchiness regression) was determined. Population density of T. postica and its parasitoid, Pales murina Mes. (Diptera: Tachinidae), was studied by Regression and Linear equation. The results showed that Taylor’s power law (R²=0.98) and Iwao’s patchiness regression, (R²=0.86), that the Konar moth larval population was aggregated on the host plant branches. As the slop of regression was significantly greater than 1, and it implies that large samples are required to obtain density estimates at an acceptable level of precision. The relationship between eating and behaviors of different larval instars fitted both Taylor’s power law and Iwao’s patchiness regression model. The slop of regression, b, was 1.99 and 3.45 for Taylor’s power law and Iwao’s patchiness regression, respectively. Then spatial distribution of fifth larval instars of T. postica on Z. spina-christi was estimated aggregated (clumped). Regression and Linear equation between mean of 5^th instar larva density of T. postica and percentage of parasitism of P. murina also showed that parasitoid acts as a density dependent factor.