Landscape connectivity shapes the spread pattern of the rice water weevil: a case study from Zhejiang, China

The spread of invasive species is a complex ecological process that is affected by both the biology of the species and the spatial structure of a landscape. The rice water weevil (Lissorhoptrus oryzophilus Kuschel), a notorious crop pest found in many parts of the world, is one of the most devastating invasive species in China, and has caused enormous economic losses and ecological damage. Little is known, however, as to how habitat and landscape features affect the spatial spread of this pest. Thus, the main goal of this study was to investigate the relationship between the observed spread pattern of L. oryzophilus and landscape structural factors in Zhejiang Province, China between 1993 and 2001. We quantified the invasive spread of the weevil in terms of both the proportion of infected area and spread distance each year as well as landscape structure and connectivity of rice paddies with landscape metrics. Our results showed that the spread of L. oryzophilus took place primarily in the southwest-northeast direction along coastal areas at a speed of about 36 km per year. The composition and spatial arrangement of landscape elements were key determinants of this unique spread pattern. In particular, the connectivity of early rice paddies was crucial for the invasive spread while other factors such as meteorological and geographical conditions may also have been relevant. To control the spread of the pest, we propose four management measures: (1) to implement a landscape-level planning scheme of cropping systems to minimize habitat area and connectivity for the pest, (2) to reduce the source populations at a local scale using integrated control methods, (3) to monitor and report invasive spread in a timely manner, and (4) to strengthen the quarantine system. To be most effective, all four management measures need to be implemented together through an integrated, multi-scaled approach.