Overwintered Are the Main Source for Infestations of the First Fruit Crops of the Season.

The mechanisms allowing the widespread invasive pest to survive from early spring until the availability of the first fruit crops are still unclear. Seasonal biology and population dynamics of were investigated in order to better understand the contribution of the early spring hosts to the infestation of the first fruit crops of the season. We identified hosts available to in early spring and assessed their suitability for the pest oviposition and reproductive success under field and laboratory conditions. The natural infestation rate of one of these hosts, , was assessed over springtime and the morphology of the flies that emerged from infested fruits was characterized under field conditions. Then, these findings were correlated with long-term monitoring data on seasonal reproductive biology and morphology of the pest, using a cumulative degree-days (DD) analysis. Field sampling revealed that overwintered females were physiologically able to lay eggs at 87 DD which coincided with the detection of the first infested early spring hosts. The latter were continuously and increasingly infested by eggs in nature from early spring until the end of May, in particular . Individuals emerged from most of these hosts were characterized by a poor fitness and a rather low success of emergence. In the field, only few summer morphs emerged from naturally infested fruits around the end of May-beginning of June. However, field monitoring in orchards revealed that individuals consisted solely of winter morphs until mid-June. These observations indicate that overwintered females are the predominant source for the infestations in the first available fruit crops of the season. We discuss these findings in the context of possible pest control strategies.