Findings on the life-cycle and on the population dynamics of Dacus oleae Gmelin in Liguria.
Population studies on Dacus oleae (Gmel.) were carried out in 1973-75 in olive groves along the coast and in the interior of western Liguria in Italy. Catches in yellow traps showed that adults were present during the whole year along the coast and in May-December inland; peak catches per trap were always higher in coastal than in inland areas. Females had the lowest numbers of eggs in their ovaries in June and the highest numbers in October; the highest numbers of females containing no eggs were caught during the peak adult emergence period, and the highest numbers of females containing numerous eggs were caught at the height of the oviposition period. The recapture rate of labelled adults released in October was low (1.4-2%) and recapture occurred only up to 50 m from the release point.By counts of eggs and larvae in the olives and of pupae in the soil it was established that 4 generations developed during the summer and autumn along the coast, with infestation beginning in early July, and 3 generations inland, with infestation beginning a month later. In the spring, up to 2 generations developed, the number depending on the number of olives remaining on the trees. The size of these spring generations appeared to be the main factor governing the rate of olive infestation later in the same year. Along the coast, where spring generations were able to develop every year, infestation was always heavy; in the interior, however, autumn infestation rates of 93 and 83% were recorded in 1973 and 1975, respectively, but only 4% in 1974 because of the low spring populations in that year resulting from the absence of olives on the trees. Other important factors regulating the Dacus populations were the low winter temperatures at the end of 1973, which affected the pupae and adults; high temperatures and drought, which affected the quality of the olives to such an extent as to cause the death of eggs and first-instar larvae inside; predation of pupae in the soil; and parasitism of eggs by Lasioptera berlesiana Paoli (Prolasioptera berlesiana) and of second- and third-instar larvae by ectophagous chalcidoids. The most important parasites of D. oleae found during this study was Pnigalio mediterraneus Ferriere & Delucchi, followed by Eupelmus urozonus Dalm. and Eurytoma martellii Domenichini; however, even high percentages of parasitism such as occurred in 1973 (80%) and 1975 (90%) did not prevent attack by the pest.