Pre-oviposition period of the ragwort seedfly,Pegohylemyia jacobaeae,introduced for the biological control of ragwort,Senecio jacobaea

Abstract

Laboratory studies on the effect of diet on the pre-oviposition period of the ragwort seedfly showed that ovarian development is not delayed by asynchrony between adult emergence and ragwort flowering, and that nutrients are required from sources other than ragwort The pre-oviposition period was, however, extended because of absence of oviposition sites. Day-degree summation (calculated from development rates measured in controlled conditions) indicated that, under temperatures in the field, females were gravid 2 weeks before oviposition sites became available. Eggs were laid on transplanted flowering ragwort before field plants flowered. Extended pre- oviposition period reduces effectiveness of ragwort seedfly as a biological control agent of ragwort as it results in poor synchronisation of seedhead damage.