Two new seed head flies attack yellow starthistle

Abstract

Six species of overseas insects have been approved for release as biological control agents of yellow starthistle, California's most pervasive weed. Previously, four biocontrol insects were known to be established in California; we now confirm the establishment of the peacock fly, as well as the accidentally introduced false peacock fly. Remarkably, the false peacock fly is significantly more widespread and more effective against yellow starthistle than the peacock fly — or any other biocontrol insect to date. However, since the false peacock fly is not an approved agent, we will await completion of our ongoing field and laboratory assessments of this fly's safety to crops and native plants before recommending use of this promising fly as a biological control agent.