Dinamica e fattori di regolazione delle popolazioni della mosca delle olive

Dynamics and regulation factors of olive fruit fly populations
The olive fruit fly, Bactrocera oleae (Rossi) (Dipt. Tephritidae), is a multivoltine pest species that can complete up to five generations per year in Italy, depending on latitude, altitude, climatic conditions and fruit availability in spring. In coastal areas, olive fly adults are observed all year round, with the highest densities in spring and autumn. Females have immature ovaries in winter, due to low temperatures, and in late spring-early summer, due to unavailability of fruits suitable for oviposition. In spring, B. oleae can complete 1-2 generations on unharvested olives, especially in high yield years, and 3-4 generations in summer-autumn. In
olive orchards at higher altitudes and in Central Italy, adults emerge in spring from overwintering pupae and oviposit on olives in summer, completing 1-3 generations per year depending on climatic conditions. Population density and intensity of fruit infestation greatly vary depending on biotic and abiotic factors, of which the most important are the climate, yearly meteorological conditions, plant cultivar, crop load, and natural enemies. In a temperate olive-growing area in north-western Sardinia, the crop yield, adult population dynamics, and fruit infestation have been studied for 10 years, as well as mortality rates of immatures inside olives and of overwintering pupae in the soil. The major mortality factors were high summer temperature in July-August, lethal for eggs and newly-hatched larvae, parasitism by Pnigalio mediterraneus on larvae, and low temperature and predation on overwintering pupae. However, the key regulation factor of B. oleae population density was natality (number of oviposited eggs), which in turn depended on the number of adults produced from previous generations. In particular, the crop yield fluctuations severely affected population abundance and degree of infestation of the olive fruit fly. Overall, the infestation rate was very higher (up to 100%) in years of lowmedium crop load than in high yield years.