Solenopsis invicta Buren, also known as the red imported fire ant (RIFA), has had a large negative impact on human and livestock health. However, few studies have further investigated the influence of human land use, which is an important factor affecting the habitats of insects, on the expansion of RIFAs. In addition, there is a lack of knowledge of the empirical associations between RIFA diffusion and land use within countries. Therefore, the objectives of this study were to provide an approach to delineate the areas of RIFA infestations and explore how land-use influences the spatiotemporal diffusion of S. invicta. We used RIFA data from 2008 to 2015 from the RIFA surveillance system, which was conducted by the National RIFA Control Center in Taiwan. Two regions in Taiwan with different RIFA infestation levels were investigated. The ordinary kriging method was applied to show the spatial intensity of RIFAs and the extreme distance estimator method was applied to determine the critical dispersal distances which showed the distance of the highest probability of RIFAs in two consecutive years. In addition, network analyses were used to identify RIFA invasion routes between land-use types. Finally, bivariate local indicators of spatial association were used to capture the invasion process in time and space. The results showed paddy fields, main roads, and warehouses were identified as the top three land-use types of diffusion sources. On average, the critical RIFA dispersal distances were 600 and 650 m in two consecutive years in high- and low-infestation regions, respectively. Finally, RIFAs were likely to diffuse between main roads and warehouses in the low-infestation region. Therefore, it is suggested that RIFA control activities be implemented at least 600 m from the observed spot. Additionally, control activities should be conducted on the identified three land-use types of diffusion sources in the high-infestation region, and the roadsides between main roads and warehouses in the low-infestation region to prevent the accidental spread of RIFAs.

The RIFA data were obtained from the S. invicta surveillance system, which was conducted by the National RIFA Control Center in Taiwan. The system included coordinates of sample tubes, collection date, and presence or absence of S. invicta in tubes. The sample tube (12 cm long × 1.5 cm radius) was a RIFA trap. The tube contained a piece of potato chip on the top (Bao, Kafle, & Shih, 2011). Potato chips are a common method used for monitoring and detecting RIFAs (Bao et al., 2011; Lin et al., 2011; Stringer et al., 2011; Vogt, Smith, Grantham, & Wright, 2003; Yang et al., 2009), and they are a frequent method used in Taiwan for RIFA sampling (Lin et al., 2011; Yang et al., 2009).

Each record stands for a location of a positive sample tube. There is no missing data. All of the sample tubes were systematically placed across the study areas except in mountain areas. In Taoyuan, one tube was placed per 200 × 200 m² in 2008. In 2009, based on the 2008 RIFA data, the tube densities were adjusted to one tube per 100 × 100 m² in highly invaded areas and one tube per 200 × 200 m² was used in the remaining areas. In 2010, Taoyuan was further divided into the high-, middle- and low-invasion areas (one tube per 100 × 100 m², one tube per 200 × 200 m², and one tube per 600 × 600 m², respectively). The tube density was reset to one tube per 200 × 200 m² in 2011. In Hsinchu, the sample density was uniform, with one tube per 200 × 200 m² in each year during the study period of 2012–2015. The column names of X and Y standards for coordinates of X and Y (CRS: TWD97-TM2).  The column names of label_C1 and label_C3 represent the types of land use.