The Colorado potato beetle, Leptinotarsa decemlineata (Say) (Coleoptera: Chrysomelidae), is native to Mexico. This important insect can completely defoliate and destroy potato crops. In 1993, it was first reported in the People's Republic of China in its northwestern Xinjiang Uyghur Autonomous Region. It spread rapidly along the northern slopes of the Tianshan Mountains from west to east at a rate of 80 km/year. Had it not been controlled when it reached the western edge of the town of Dashitou in Mori Kazakh Autonomous County in 2003, it very likely would have threatened potato production in Gansu Province, China's main potato producing region. Previous studies have documented the life history, chemical control methods, insecticide resistance, and other information, but the effects of environmental factors on its distribution have rarely been studied. Rivers often play an important role as corridors for pest invasion while providing water for crop production in arid and semiarid regions. What role are rivers playing in the spread of the Colorado potato beetle in the northern areas of the Xinjiang Uyghur Autonomous Region? This paper addresses the spread of the Colorado potato beetle in Shawan County by determining the role rivers are playing in its distribution in riparian habitats, using the spatial analysis tools of ArcGIS 8.3 software.
Survey data indicate the Colorado potato beetle was first found in the towns of Boertonggu, Xigebi, and Dongwan in Shawan County in 1998. Damage levels to crops reached level four in these towns and the surrounding areas, the highest level. These areas were all more heavily impacted than other towns where this beetle arrived later. As the Colorado potato beetle spread from south to north along riparian habitats, the degree of impact gradually declined so that northern towns and areas received less impact. The beetles arrived in central and northern Shawan County in areas around the towns and townships of Jinggouhe and Wulanwusu in 1999 and in Sidaohezi, Laoshawan, Liumaowan, and Shanghudi in 2000. The ArcGIS Directional Distribution (Standard Deviational Ellipse) tool was used to determine whether the distribution of the Colorado potato beetle exhibits a directional trend when compared with the direction of river flow in Shawan County. The results suggest the direction of the spread of Colorado potato beetle and the direction of river flows coincide; both go from south to north in Shawan County. The ArcGIS buffer zone tool was used to study the level of damage caused by Colorado potato beetles as they spread following water channels in riparian habitats. The damage levels from Colorado potato beetles were documented by calculating a series of nested buffer zones. A series of five 1-km-wide nested buffer zones were created along the rivers of the study area, with the combined buffer zones extending 5 km on each side of each river. The results show beetle impact was significantly different in each buffer zone: buffer zone 2 (1-2 km) > buffer zone 4 (3-4 km) > buffer zone 5 (4-5 km) > buffer zone 1 (0-1 km) > buffer zone 3 (2-3 km). Habitats along rivers also showed significantly different impacts from beetles: Jinggou River > Anjihai River > Manas River > Xi'an Canal.