Effect of elevation on spatio-temporal patterns of olive fly (Bactrocera oleae) populations in northern Greece

Abstract

The spatio-temporal patterns of olive fly populations in a managed olive-growing region in the area of Chalkidiki in northern Greece were followed during 2005. The trapping grid consisted of 700 traps. Throughout the growing season (July-October), McPhail traps loaded with ammonium sulphate were inspected at 5-day intervals. Trapping data were analysed using Getis-Ord local spatial statistics. Clustering of trapped flies was significantly related to elevation, which ranged from sea level to 700 m above sea level. The effect of elevation upon clustering depended on seasonal climatic patterns. During the summer, 'hot-spots' (i.e. significant aggregations of captured insects) were located at intermediate to high elevations and 'cold-spots' (i.e. areas with significantly low numbers of captured insects) were found in the valleys. In contrast, during the fall, 'hot-spots' were detected at lower elevations and 'cold-spots' at higher elevations. Population phenology seemed to affect spatial patterns. During periods of low population levels across the entire region, clusters of traps with relatively high amounts of captured insects were found at lower elevations. Pest management activities may have affected population levels throughout the region, but our data set does not allow quantifying their effectiveness. Our data suggest that differences in environmental temperature, as a result of altitudinal cline and season, may affect both the size of the olive fly population and its spatial patterns. The implementation of spatio-temporal analyses for management of the olive fly is discussed.