Relationships between spatial pattern of Locusta migratoria manilensis eggpods and soil property variability in coastal areas

Spatial distribution of Locusta migratoria manilensis eggpods and soil properties (water content at 5 cm depth, salinity, organic matter and pH) was studied by integrating geostatistical analysis and GIS techniques. During 2 years of surveys over the entire study area (6000 ha), extensive data (292 regularly grids with 450-m intervals), coupled with intensive data (2601 regularly grids of 0.5-m separation) were used to characterize spatial patterns of L. m. manilensis eggpods and soil property variability and to explore the relationship between them. Semivariograms indicated the eggpods and four soil properties showed high spatial heterogeneity. The spatial distribution of eggpods, at distances ranging from 50-452 m in spatial autocorrelation, was best described using the spherical model. Spatial autocorrelation in total spatial heterogeneity in soil water content at 5 cm, salinity, organic matter and pH were 76.15, 78.04, 57.19 and 61.85%, respectively, and the scales of spatial heterogeneity were 621, 594, 1014 and 1368 m, respectively. GIS assessment maps of eggpods and soil properties, derived by block kriging, displayed patterns of the locust eggpods and soil property variability at an area-wide scale. Most eggpods (66.27% and 72.24% for 2002 and 2003, respectively) were found at the areas with low salinity (<2.0% approximately), suitable water content at 5 cm (10.1-20.0%). No eggpods were found at such areas with high soil water content at 5 cm (>30%) and salinity (>3%). In a way, the spatial distribution pattern of locust eggpods mainly depended on the soil heterogeneity at the study area. t-Tests indicated that sites between with eggpods and without eggpods were significantly different only in soil water content at 5 cm depth and salinity. The results may provide useful information on sampling in the field, forecasting and monitoring locust plague and reclaiming coastal locust breeding areas in China.