Population density and spatial distribution pattern of Hypera postica (Coleoptera: Curculionidae) in Ardabil, Iran

Abstract

The alfalfa weevil, Hypera postica (Gyllenhal), feeds almost exclusively on alfalfa, Medicago saliva L. in most region of the world where forage crop is grown. It has been investigated the population density and spatial distribution of alfalfa weevil on alfalfa in Ardabil during 2010. Using a 0.25 m(2) quadrate sample unit a reliable sample size was 65, with maximum relative variation of 15%. The relative variation (RV) of the primary sampling data was 13.6. The highest population density of the alfalfa weevil was recorded on 17(th) April. To estimate the spatial distribution pattern of this pest, data were analyzed through index of dispersion. Lloyd's mean crowding. Morisita's index and two regression models (Taylor's Power Law and Iwao's Patchiness Regression). Taylor's model showed an aggregated distribution pattern for all life stages. Iwao's patchiness regression indicated that larvae, adult and total life cycle had aggregated spatial distribution (t(c