Reliability of methods used to estimate rodent pest densities in agricultural systems: the case of common vole (Microtus arvalis) in NW Spain

Abstract

For pest management strategies to effectively prevent crop damage while at the same time causing the least environmental collateral damage, reliable abundance monitoring tools are required. The common vole is a major agricultural pest in Castilla y León (NW Spain). In this study we compared common vole density estimates provided by two indirect indices, the Presence Signs per Square (PSpS) index, previously evaluated by a comparison with the trapping methodology most accepted to estimate rodent densities, and another one (MI), proposed by the Spanish Ministry of Agriculture Food and Environment, which is currently recommended as main monitoring tool for this pest, but that apparently has not been evaluated in a similar way. We found that at low vole abundance, MI generated much larger vole density estimates (on average 14 times) as compared to PSpS, although both indices were highly correlated. These results strongly support that abundance estimates provided by MI must be considered potential overestimates of real vole density and must be corrected accordingly in the future, if the method is to be kept as a main monitoring tool of vole density. Our results reinforce the importance of evaluating this kind of monitoring tools in different density scenarios to prevent the start or continuation of control campaigns when they are unnecessary, thus reducing their associated economic and environmental costs.