The effect of the expansion of the agricultural frontier on insect pest populations in Argentina.

GRILLI, M.P.; GLEISER, R. M.; RAVELO, A.C.

Spot Vegetation User Proceedings.

Office for Official Publication of the European Communities

Lugar: Antwerp; Año: 2004 vol. 2 p. 181 - 182

The expansion of the agricultural frontier in Argentina has been growing at a high rate during the last decade, encouraged by the pricing of soya beans and other crops. Areas that were traditionally devoted to extensive farming on natural grasslands and woodland are being depleted at a high speed. It is expected that such abrupt changes in the ecosystem will have an effect on the presence and dynamics of insect pests. A five year time series analysis was performed on SPOT Vegetation over two areas in Córdoba province, central Argentina. The first area, to the south east of the province (62º 52´ W, 33º S) is historically an annual crop area (mainly soya bean, maize and wheat). The second area, to the north of the province (63º 54´W, 30º27´S), was until recently a mixture of cattle grasslands and natural woodland, and currently is been displaced by annual crops (mostly soya bean). A characterization of the typical agricultural seasonal profile was extracted by averaging a five year decadal period from 1998 to 2003 from the southern sample site (6 x 6 Km). Each year profile from the north area was compared to the typical agricultural seasonal profile, by correlation analysis. It was expected that as the cropped area increased, the Pearson correlation index would approach to one. It was shown that there is an increasing significant positive relationship between the North and South NDVI as expected (r = -0.2 in 1998 to r = 0.80 in 2003). These changes in NDVI showing the expansion of the agricultural frontier are consistent with a preliminary comparison of land use for the same area and period using Landsat Tm 5 imagery. Our results indicate that SPOT Vegetation is a useful tool to asses rapid changes in land cover and usage, in this case large changes in the agroecosystem in central Argentina. These changes will certainly affect  insect pests populations in different ways. Population growth may increase in some species, becoming new agronomic pests (e.g. Isopoda in soya bean in Argentina), and also lead to more frequent contact between formerly separated species, offering an opportunity for new pathogen, vector and host interactions (e.g. vector borne diseases such as Western equine encephalitis, Lyme disease, Leishmaniasis). SPOT Vegetation images can provide data over a broad surface and can be use in analytical methods to rapidly increase our understanding of the potential distribution of insect pests and of the regional factors affecting their population dynamics.