Overwintering Capacity of the Mediterranean Fruit Fly in the Dalmatia Region of Croatia

The Mediterranean fruit fly, <i>Ceratitis capitata</i> (Wiedemann) (Diptera: Tephritidae) is considered one of the most important phytophagous pests worldwide. In Croatia, it severely affects the fresh fruit production in Dalmatia, and a national suppression action plan has been established to alleviate farmers' burden. The aim of the current paper was to comprehensively study the overwintering dynamics of medfly in Dalmatia and investigate whether adults and pupae in addition to larvae can overwinter in different conditions, with a goal to support the establishment of a sound off-season control strategy against this pest. The off-season strategy, which was recently proposed in the frameworks of the EU Horizon 2020 funded project FF-IPM, focuses on the management of the low adult populations during winter and early spring period that has a detrimental effect on the development of the on-season summer and early autumn populations. Overwintering trials were conducted in Split (Dalmatia region, Croatia) using the local <i>C. capitata</i> population. Cages with different life stages (adults, pupae) or infested fruits were periodically transferred in three overwintering sites (open-field, semi-field, and urban conditions) from October to December (two to three establishment dates during the 2019-2020 and 2020-2021 season). Our results provide strong evidence that, in addition to larvae within fruit, both adult and pupae can survive in significant proportions in open-field and urban conditions. Overwintering site and establishment date were both significant predictors of the overwintering success of adults, and they affect pupae developmental duration, adult emergence rates from overwintering pupae, female fecundity, and generally the overwintering ability of the pupae. Our results suggest that the current national strategy for <i>C. capitata</i> suppression, which is based on the assumptions of larvae overwintering need to be adjusted by development and implementation of the off-season strategy.