Natural enemies of rice insect pests harbored in heterogeneous habitats around rice fields have been identified as the natural agents for sustain- able rice pest management for a long time (Way and Heong 1994). However, the movement of rice arthropods must be investigated to analyze the sensitivity of the natural enemies in tracking insect pests. In this study, the movement of rice arthropods along a rice transect is detected by using an algorithm for detecting boundaries of ecological transects in order to find and confirm mechanisms for natural and sustainable control of rice insect pests by their natural enemies.
A transect along the east-west direction and traversing 6 ha of rice fields and uncultivated habitats on the IRRI upland farm was established (Fig. 1). Transect sites were spaced at approximately 5-m intervals and were sampled for arthropods and vegetation every 2 wk in the growing season, using a suction sampler with a O.16-m2 enclosure and pin-frame sampler, respectively. Edges in the land- scape were distinguishable as roads (o), borders between rice and natural vegetation (r- w), rice bunds (b), and rice-rice bund-rice (rbr), etc. Laboratory sorting treated different life stages (immatures, adults) separately. Data from the records were stored as a site- by-taxa matrix. Nine transects were obtained for arthropod categories and sampling dates (predaceous, parasitoid, and herbivorous arthropods, each with three transects at three sampling dates).