Biology, ecology and behaviour of Baryscapus silvestrii (Hymenoptera: Eulophidae), a gregarious pupal parasitoid of fruit-infesting flies

Baryscapus silvestrii (Hymenoptera: Eulophidae), a gregarious parasitoid of the olive fly Bactrocera oleae (Diptera: Tephritidae), has become the predominant parasitoid in some areas of the Campania region (Southern Italy). However, when it was described, its biology was largely unknown. Initial attempts at establishing a laboratory rearing on the olive fly failed, whereas the medfly Ceratitis capitata (Diptera: Tephritidae) turned out to be an ideal alternative host. Having established a laboratory rearing, we could evaluate several biological and ecological traits on different hosts: B. oleae, Rhagoletis cerasi, R. completa (Diptera: Tephritidae) and Drosophila suzukii (Diptera: Drosophilidae) were carried out. Choice tests with puparia of different ages and different species were also performed. Baryscapus silvestrii completed development only if reared on B. oleae, R. completa and C. capitata. No adult emergence was recorded at temperature of 15°C, while the developmental time from egg to adult decreased with increasing temperature from 20 to 30°C. Furthermore, it was able to develop on puparia of different stages, although it preferred 3-4 day-old puparia. The life cycle of some wasps was much longer than others, but when females were allowed to oviposit for 24 hours only such differences disappeared. Baryscapus silvestrii performs destructive host-feeding: the number of hosts killed by host-feeding is similar to the number of hosts parasitized, therefore host feeding doubles the effectiveness of the parasitoid, showing its potential for the biological control of different fruit fly pests.