Unintentionally ReleasedChaetorellia succinea(Diptera: Tephritidae): Is This Natural Enemy of Yellow Starthistle a Threat to Safflower Growers?

Abstract

Abstract In mid-1996, we detected an unintentionally introduced seed-head fly, Chaetorellia succinea (Costa), destroying seeds of yellow starthistle, Centaurea solstitialis L., one of the worst weeds in the western United States. In overseas studies, Chaetorellia succinea had been considered as a potential biological control agent for yellow starthistle, but had been rejected because of fears that it might become a pest of safflower, Carthamus tinctorius L., in the United States. From mid-1996 through early 2000, we conducted both laboratory and field evaluations to determine whether this fly could cause significant damage to safflower, a widely planted crop in California. In laboratory no-choice host range evaluations, adult females would oviposit, and the larvae completed development, on all five varieties of safflower that we tested. However, in choice tests, only one head each of two varieties of safflower was attacked. No safflower was attacked at three sites in California and Oregon, with large popu...