The role of landscape structure on the abundance of a disease vector planthopper: a quantitative approach

Studies of patchily distributed insect populations have made clear the importance of host patch size and degree of isolation in determining the distribution of these populations. For such populations, patch connectivity will have an effect on patterns of patch occupancy and regional dynamics. In the present study we performed a series of observations to estimate the effect of landscape structure on the abundance of Delphacodes kuscheli (Homoptera: Delphacidae), vector of “Mal de Río Cuarto” disease to maize. Actively dispersing D. kuscheli individuals were collected in 19 sampling sites during the spring of 2004, using sticky traps placed at 2 m above ground level. Land use and landscape pattern were quantified, using Landsat 5 TM images for the area where each sampling site was placed. Four land use categories were considered in the analysis; winter pastures, winter cereals, perennial pasture and stubble. The spatial pattern analysis program FRAGSTATS was employed to estimate the patch area, patch proximity index, Total Class Area and the Mean Proximity Index for each of the land use categories in those sites where insect samples were taken. Partial Least Squares Regression analysis techniques were employed to relate the mean abundance of D. kuscheli and the landscape measures. Eighty percent of the variation of the mean insect abundance was explained by two first PLSR components. The proximity index of the local host patches, the amount of area left to stubble, local host patch area and total area of winter pastures were the most important variables affecting the abundance of dispersing D. kuscheli individuals. We found that the abundance of the dispersive fraction of the population of D. kuscheli is affected mostly by the surrounding landscape, particularly by the proximity of other host patches, and the permeability of the matrix represented by the stubble.