The western tarnished plant bug (Lygus hesperus) is a key pest in many crops in the San Joaquin Valley (SJV) including cotton, dry beans, seed alfalfa, and various fruits and vegetables. Populations of this indigenous insect begin at very low densities in spring but build through the summer on a variety of host plants. As one plant or crop becomes unsuitable the insect moves into neighboring crops. Geographic Information Systems (GIS) provides an ideal tool to study the concentration and movement of lygus through the season. GIS techniques were used to characterize various landscapes in the study area that provide lygus habitat. Several townships were analyzed throughout the valley in general to identify differences in cropping patterns, and specifically to investigate the pattern of cotton and alfalfa adjacency. In addition, Landsat imagery was processed to identify areas of senescing natural vegetation that are in close proximity to cultivated areas. Finally, actual lygus population dynamics in bordering farm areas were mapped using real-time field data. These approaches provide a powerful tool to understand the landscape in lygus population development and movement. The concept of crops and plants acting as sources out of which lygus move or sinks into which lygus move can be studied on a regional scale. The role of individual crops such as alfalfa hay on the intensity of lygus in an area might be used in a predictive manner to prescribe regional management of this pest. GIS also provides useful tools to help cotton growers and consultants visualize complex crop interactions and lygus movement.