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Delphacodes kuscheli Fennah is the vector of maize rough dwarf virus, that affects maize production in central Argentina. The spatial and temporal abundance pattern of the insect vector was studied from October 1992 to November 1994, within endemic and non-endemic areas of the crop disease. Insect density was estimated every 7-15 days during spring and summer (maize season) or monthly during autumn and winter from high (6 m) and low (1.5 m) sticky traps placed at eight sampling stations along a 300 km transect. Each year, D. kuscheli density increased from October, peaked in December, to decrease afterwards and disappear in May. Density was lower in the nonendemic area and higher in the endemic one. The average absolute difference of density between sampling station pairs increased with the distance between the sampling stations (R 2 =0.85), and the correlation of density changes decreased with the distance between the sampling stations (R 2 =0.78), suggesting that the population dynamics were affected more by local than by regional factors. There was a significant correlation (with a 36 days lag) between the normalized difference vegetation index (NDVI) (calculated from 15 days maximum value composites images of NOAA-11 meteorological satellites) and D. kuscheli abundance. Based on this regression model, and using the time series of the satellite derived NDVI values, maps of the distribution and abundance of D. kuscheli within the study area for the spring and summer of 1992 were produced.

The effect of host patch area and configuration on the abundance of dispersing individuals of Delphacodes kuscheli Fennah (Homoptera: Delphacidae), the vector of Río Cuarto disease in maize, was investigated in the main maize production area of Argentina. Actively dispersing D. kuscheli individuals were collected from 15 sampling sites during the spring seasons of 1999 and 2000, using sticky traps placed at 6 m above ground level. Host patches were detected and quantified using Landsat 5 TM images for the periods studied. The spatial pattern analysis program FRAGSTATS was used to estimate the total class area, largest patch index, mean proximity index, and patch cohesion index for patches of winter pastures (the main insect host during winter) as observed from the satellite images. Landsat 5 TM estimations showed local variability in the proportion of winter pastures, with patches bigger during 1999 than during 2000, but these patches represented only a very small part of the total landscape. Proximity between host patches was also variable between sites and higher values of cohesion occurred during the first sampling season. The relationship between host area and D. kuscheli mean abundance was adjusted to an exponential (R2= 77.5%) model. Host patch dominance, host patch isolation, and host patch connectivity all showed a positive relationship with D. kuscheli mean abundance, adjusting significantly to linear models (R2= 92%, R2= 90%, and R2= 22%, respectively). Outbreaks of Río Cuarto disease in the main maize production area of Argentina are related to high vector populations. The results indicate that the abundance of D. kuscheli depends on factors related to the abundance and configuration of its host patches.

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