The use of the cumulative degree-days to predict olive fly, Bactrocera oleae (Rossi), activity in traditional olive groves from the northeast of Portugal

Abstract

Terra Quente, situated in the province of Tras-os-Montes (northeast of Portugal), is one of the most important olive growing areas of Portugal. In this region, which is extremely hot and dry during summer, losses due to the olive fly, Bactrocera oleae (Rossi), are highly variable between years, with estimates ranging from 16.3 to 98.8% of infested fruits. The objective of this study was to test the use of the degree-days models, based in a daily accumulation of temperature (°DD) to predict insect activity in the field and timing control measures, in such a climatic condition. Seasonal flight activity periods and insect development were studied from 2005 to 2008 in traditional olive groves and a degree-day model was developed for predicting the development of olive fly second generation, which is the one that can cause losses. It was found that, while the use of these models could be hampered by high temperatures and low relative humidity prevailing during summer, they may have some potential as a tool for the management of B. oleae populations, allowing the identification with acceptable error of the main second generation events. Results indicated that, if adulticide sprays are to be used, the spray-window for their applications lasts between an accumulation, since January 1, of 1837.20 ± 35.82°DD8.99, which corresponds to the beginning of the insect second flight and 2045.87 ± 34.30°DD8.99, which corresponds to its main peak.