Peculiar behavioural and biological traits of Baryscapus silvestrii (Hymenoptera: Eulophidae), parasitoid of Bactrocera oleae and Ceratitis capitata

Baryscapus silvestrii is a gregarious endoparasitoid of the olive fly Bactrocera oleae recently described from Southern Italy. Over the last 15 years, B. silvestrii has expanded its distribution range becoming the predominant parasitoid in some areas of the Campania region. Biological and behavioural data on this parasitoid are scarce because previous attempts of rearing it on B. oleae in the lab were unsuccessful. We have managed to rear it on the Medfly Ceratitis capitata, and evaluated the following traits: sex ratio, suitable and preferred host age, ovigeny index, mating behaviour, developmental time, longevity, progeny, oviposition period. B. silvestrii is biparental, but on C. capitata it shows a female-biased sex ratio. It parasitizes its hosts only if puparia are at least partly concealed or if they are in a confined environment, and it is able to develop on puparia of different stages, from those just formed up to those close to adult emergence. Wasps usually lay eggs into the host’s abdomen, larvae first feed inside the abdomen without killing the host up to the point where their development is almost complete, then they feed on the entire host body. B. silvestrii is, indeed, only briefly koinobiotic; besides it is synovigenic, proterandric and performs host-feeding. Males often wait to mate with emerging females inside the pupal host, resulting in sibmatings. Development varied greatly because adult emergence at 25°C is staggered, as most adults emerged after 20 days, whereas a portion of them took up to seven times longer. Life span of adults at 25°C was 56 days, the mean progeny per female was 140 and the oviposition period lasted 33 days. B. silvestrii has peculiar biological and behavioural traits that show its potential for the biological control of both fruit flies.