Geostatistical analysis of spatial distribution of Therioaphis maculata (Hemiptera: Aphididae) and coccinellid lady beetles (Coleoptera: Coccinellidae)

Understanding the spatial dynamics of insect distributions provides useful information about their ecological requirements and can also be used in site-specific pest management programs. Interactions between prey and predator are spatially and temporally dynamic and can be affected by several factors. In this study, geostatistics was used to characterize the spatial variability of spotted alfalfa aphid, Therioaphis maculata Buckton and coccinellid lady beetles in alfalfa fields. Global positioning and geographic information systems were used for spatial sampling and mapping the distribution pattern of these insects. This study was conducted in three alfalfa fields with areas of ۷.۳, ۳.۱ and ۰.۵ ha and two growing seasons, ۲۰۱۳ and ۲۰۱۴. The ۰.۵ ha field was divided into ۱۰ × ۱۰m grids and ۳.۱ and ۷.۳ ha fields were divided into ۳۰ × ۳۰m grids. Weekly sampling began when height of alfalfa plants reached about ۱۵cm and was continued until the cuttings of alfalfa hay. For sampling, ۴۰ and ۱۰ stems were chosen randomly in ۳۰ × ۳۰m and ۱۰ × ۱۰m grids, respectively and shaken into a white pan three times. Aphids and coccinellids fallen in the pan were counted and recorded. Semivariance analysis indicated that distribution of T. maculata and coccinellids was aggregated in the fields. Comparison of the distribution maps of aphid and lady beetles indicated that there was an overlap between the maps, but they did not coincide completely. This study revealed that relationship between spotted alfalfa aphid and lady beetles was spatially dynamic. These results can be used in biological control and site-specific management programs of T. maculata.