On the spatial spread of the Rice water weevil, Lissorhoptrus oryzophilus Kuskel (Coleoptera: Erirhinidae), in Italy

A five year study has been made to establish the spread of the rice water weevil Lissorhoptrus oryzophilus (Coleoptera: Erirhinidae) in Northern Italy. Data obtained with GPS from 2005 throughout 2009 were first georeferenced with SW ArcGis® 9.2, then overlapped and compared to the map of the European environmental landscape based on the interpretation of satellite images (CORINE Land Cover map) and to the hydrographic chart CT10 (Technical Regional map 10000). The analysis of the radial rate of spread per year indicates a deceleration in the expansion from 10.864 ± 6.801 km/year in 2005 to 5.318 ± 1.401 km/year in 2009. In five years the weevil has expanded its distribution in nearly all rice paddies in Lombardy and Piedmont, over an area of about 200,000 ha, which correspond to 86% of the total Italian rice area. Its expansion is thought to follow a type of stratified dispersal, due both to insect adult active dispersal and to accidental movements caused by human transportation