Spread parameters of the borer Xylotrechus Arvicola (Olivier) (Coleoptera: Cerambycidae) in a 'Tempranillo' vineyard in la Rioja (Spain): A long-term study

Xylotrechus arvicola (Olivier) (Coleoptera: Cerambycidae) is a polyphagous xylophagous beetle that is becoming a pest of increasing importance for vineyards in Spain, also because of the wood fungi developing in the galleries excavated by its larvae, which cause a progressive decline of the affected grapevines, until death. Between 1993 and 2015, a survey of the infestation caused by X. arvicola and the symptoms caused by pathogenic wood fungi was performed in a 'Tempranillo' variety vineyard in La Rioja region (Spain). Maps showing the overtime spread of the borer and the diffusion of symptoms of grapevine decline and Eutypa dieback were obtained. Results indicated that the borer colonization began in the centre of the plot, followed by the first symptoms caused by the wood fungi a few years later. The statistical analysis showed that the evolution of infestation is characterized by a linear increase of new holes whereas the pattern of their allocation in the vines follows a bimodal distribution which, to some extent, can be simulated by a Poisson's model. Based on these observations, a methodology to estimate the state of the infestation over time is proposed. The procedure - based on a linear regression of the average number of holes per vine over a set of years - can be applied in a relatively simple way and provides the probability for a grapevine to have a certain number of exit holes in a definite year with a mean error of around 5%.