Bactrocera oleae reproductive biology: new evidence on wintering wild populations in olive groves of Tuscany (Italy)

Bactrocera oleae (Rossi) (Diptera Tephritidae) is the most alarming pest of the olive tree. Nevertheless, the reproductive cycle of overwintering populations of this pest in the spring is still unclear. A better understanding of the reproductive cycle over the year can lead to testing new strategies in preventive adult treatment scheduling, thus reducing the populations in the following summer when fruits are set. Adult flights of overwintering populations of B. oleae have been described for two areas of Tuscany. A degree day model for the overwintering population of B. oleae was applied to adult emergence in spring. We monitored the reproductive cycle of this pest during two years. Insect morphology and oviposition activity of B. oleae females caught by traps in the two sampling areas in the spring were studied by dissecting and observing the whole mount reproductive apparatus under a stereomicroscope. The observation of ovaries containing follicular relics and the presence of sperm cells in most ovipositing females validated the occurrence of egg fertilization and, therefore, the presence of a complete generation in the spring. The tested degree-day phenological model for adult emergence from autumn oviposition was proved useful in studying the population dynamics of B. oleae. The 50% of cumulative captures (male plus female) was reached in the first half of April, with few days of difference between years and sites. Olive fruits collected in the spring, in coincidence with flight peak, showed between 10 and 20% of active infestation. Understanding the complex interactions between reproductive biology of B. oleae and the surrounding environment might lead to potential new approaches in integrated pest management programs.