Intra-annual continuous reproduction of the apple pest Microtus lusitanicus: Implications for management

Abstract

The Lusitanian pine vole (Microtus lusitanicus) is a key pest of apple in Asturias (NW Spain). The sustainable management of populations of this vole requires a deep knowledge of relevant aspects of its biology and ecology. To improve our knowledge on the breeding characteristics of M. lusitanicus, we analysed a sample of 700 individuals collected monthly in apple orchards during two years. The continuous occurrence of immature specimens and pregnant females during the whole study period indicates that M. lusitanicus can breed continuously throughout the year in apple orchards in Asturias. The relatively mild weather conditions in winter and the presence of a permanent grass cover throughout the year seem to be favourable conditions for continuous breeding of the vole. Nevertheless, some data (decrease in the size of testes and seminal vesicle of mature males in winter, lower percentage of pregnant females in December and of non-mature specimens in March) suggest that reproduction activity decreases slightly in winter. Mean litter size was relatively low in comparison with that reported for other Microtus species. The balanced adult sex-ratio and the relatively small testis size are congruent with a monogamous mating system. Nevertheless, the frequent coexistence of matures with two or more other adult voles of the opposite sex, and even the cohabitation of one male with two pregnant females, suggest that monogamy was facultative in our population. This study adds significantly to the current knowledge on the biology of this vole pest and can help in the design and implementation of sustainable and efficient management plans. As a first step, control practices should be deseasonalized and applied throughout the year.