Spatial Distribution of Oriental Migratory Locust (Orthoptera: Acrididae) Egg Pod Populations: Implications for Site-specific Pest Management

We studied the spatial distribution of Locusta migratoria manilensis (Meyen) egg pods by integrating geostatistical analysis and a geographic information system (GIS) techniques. During 2 yr of extensive surveys, egg pod data were collected over two spatial scales: 292 regularly grids with 450-m intervals over the entire study area (6,000 ha), and 2,601 regularly grids of 0.5-m separation in potential oviposition areas located on the slopes, damaged by the locust plague or covered with sparse vegetation. Ecological variables included vegetation cover, topography (aspect and slope), and soil parameters (salinity, pH, moisture at 5 cm, organic matter). Results showed that most egg pods (66.27 and 72.24% for 2002 and 2003, respectively) were found on south-facing and southwest-facing slopes with sparse reed cover (0 approximate to 30%), low soil salinity (< 2.0%), and suitable soil moisture at 5 cm (10.1 approximate to 20.0%). t-Tests indicated that sites between with egg pods and without egg pods were significantly different in vegetation cover, sun index (combination of aspect and slope), soil moisture at 5 cm depth, and salinity. Semivariograms showed spatial autocorrelation in egg pod distribution at distances ranging from 0.5 to 452 m. The spatial distribution of egg pods was best described using spherical models. GIS risk assessment maps, derived by block kriging, displayed the probabilities of occurrence of the locust egg pods at an area-wide scale. The results may provide useful information on planning for site-specific pest management. Targeted monitoring and spraying can be effectively used during the peak hatch in the following spring.