Vitis 49 (2), 67–70 (2010) Evolution of the spatio-temporal distribution of Xylotrechus arvicola (Olivier) (Coleoptera, Cerambycidae) in La Rioja vineyard (Spain) R. OCETE 1) , J. M. VALLE 2) , K. ARTANO 2) , M. E. OCETE 1) , M. ÁNGELES LÓPEZ 1) , M. ÁNGELES PÉREZ 1) , D. GARCÍA 3) and F. J. SORIA 1) 1) Laboratorio de Entomología Aplicada, Departamento de Fisiología y Zoología, Universidad de Sevilla, Sevilla, Spain 2) Escuela Universitaria de Ingeniería de Vitoria-Gasteiz, Universidad del Pais Vasco, Vitoria-Gasteiz (Álava), Spain 3) C/ El Salvador, 12, Tirgo-La Rioja, Spain Correspondence to: Prof. Dr. M. ÁNGELES LÓPEZ MARTÍNEZ, Laboratorio de Entomología Aplicada, Departamento de Fisiología y Zoología, Universidad de Sevilla, Avda. Reina Mercedes 6, 41005-Sevilla. amene@us.es Summary Xylotrechus arvicola (Olivier) (Coleoptera, Cer- ambycidae) is a polyphagous species. Its larvae can be found feeding on different wooden cultivars and wild trees. Since 1990, this pest has become an important sanitary problem affecting vineyards in northern and central Spain (2000-2008). A study based on the distri- bution of the number of exit holes perforated by adults in the vinestocks was carried out for 9 years in a plot located in La Rioja wine producing region (Spain). The percentage of affected plants grew each year, from 51 % in 2004 to a level of 96 % in 2008. In 2005, dead vines began to appear with damage caused by the in- sect. In 2008 it increased to 17 % of the vines. This data indicated a very heavy attack of the insect which is be- coming a very serious pest. The number of exit holes is directly related to the number of affected vinestocks and also dead plants. The spatial distribution of the holes of X. arvicola was studied using Taylor´s Potential Law and Iwao´s regres- sion, as well as elaborating maps of population density. Statistical techniques indicated a uniform distribution of the pest in the sampling plot. During the cited period, several aggregation centers could be observed with a long term spatio-temporal stability using the Cramér- Von Mises test. K e y w o r d s : aggregation centers, distribution, exit holes, maps of infestation, Tempranillo cultivar. Introduction The vineyard of La Rioja covers an area of about 65.000 ha. Based on the quality of its products, it consti- tutes the only Spanish Qualified Denomination of Origin and one of the main wine-producing regions in the world. 'Tempranillo' occupies almost 75 % of this area. It is con- sidered the most representative autochtonous red grapevine in Spain with a heavy presence in several other Denomina- tions of Origin (HUETZ DE LEMPS 2009). During the second half of the decade of 1970, in the Northen part of La Rioja, named Rioja Alta, the first symp- toms of infestation caused by larvae of cerambicidae were detected inside the wood of the vinestocks at pruning time. Larvae were commonly known as the screw, due the coni- cal outline of the preimaginal phases. Its incidence was more frequent in those plots situated in the vicinity of the rivers Oja, Tirón and Ebro rivers, because it constitutes a pest of several trees situated along river bank forests, such as Populus, Salix, Ulmus, etc. At the same time, adult exit holes, of about 4 mm in diameter, were also observed, both in the trunk of the vines as well as in the bigger branches of the vine. The identification of the coleopterans from mate- rial developed in the laboratory from samples of vine wood and captured in the field corresponded to Xylotrechus arvi- cola (Olivier) (Coleoptera, Cerambycidae), according to OCETE and DEL TÍO (1996). X. arvicola is a polyphagous species with a holomedi- terranean distribution. In Spain, it is distributed, mainly, from the North to the Central regions, and there is available data of capture in the Basque country and the Balearic Is- lands. Other references on the presence of this species can be found in Southern Spain, to be precise, in the Alicante and Granada provinces (VIVES 1984, BAHILLO 1995). The infestated vinestocks with a traditional training en vaso (a kind of short pruning) or conducted on trellis ex- hibit rachitic shoots with a low vigour, very similar to those caused by the fungal disease Eutypa dieback. Galleries of larvae provoke a heavy reduction in production and later the death of the branches, and finally, caused the death of the plant. In Spain, the incidence of this new sanitary problem became more intense at the beginning of the decade of 1990 due to unknown causes (OCETE and DEL TÍO 1996). So, the pest spread to other vineyards belonging to the communities of Castilla-La Mancha, mainly on 'Cabernet Sauvignon' and 'Cencibel' ('Tempranillo'); Castilla y León, on Tinta del país ('Tempranillo') and 'Sauvignon blanc', and 'Navarra', 'Garnacha tinta', 'Tempranillo', 'Moscatel' and 'Miguel del Arco' (LÓPEZ et al. 2002, OCETE et al. 2002 a, c and 2004). In this last community, plantations of Prunus spinosa, whose berries are macerated in liquor to produce pacharán, a very popular distilled drink, are also being at- tacked intensely by this xylophagous coleopteran (BIURRUN et al. 2007). The level of infestation of this plague is influenced by the kind of cultivar, the pruning type and the age of the vines, according to the conclusions of several field prospections carried out in different Guarantee of Origin (A.O.C) of Castilla and León by PELÁEZ et al. 2001, GARCÍA