Tuesday, December 11, 2007 - 3:59 PM

Attack on trap plants of a native knapweed by Chaetorellia succinea (Diptera: Tephritidae), an unintentionally-released natural enemy of yellow starthistle

Joe K. Balciunas, joe@pw.usda.gov1, Baldo Villegas, bvillegas@cdfa.ca.gov2, and Chris N Mehelis, mehelisc@pw.usda.gov1. (1) USDA-ARS, Exotic & Invasive Weed Research Unit, Western Regional Research Center, 800 Buchanan St, Albany, CA, (2) California Dept Food & Agriculture, Biological Control Program, 3288 Meadowview Rd, Sacramento, CA

Yellow starthistle, Centaurea solstitialis, is one of the most pervasive and damaging weeds in western USA. It has been a target for biological control for a half-century. In 1991, while releasing the approved Chaetorellia australis (Diptera: Tephritidae), a second fly species, Chaetorellia succinea, was also inadvertently released in southwestern Oregon. This second fly established and spread rapidly, and is now the most common natural enemy of yellow starthistle in California. Earlier, in our laboratory tests, we showed that Ch. succinea might also attack a native knapweed, American basketflower, (Centaurea americana). During 2006, we grew ‘trap plants’ of two varieties of American basketflower at three field locations in northern and central California where Ch. succinea was abundant. At all three locations, American basketflower was infested by this fly, but seed reduction was much less than on yellow starthistle.

Species 1: Diptera Tephritidae Chaetorellia succinea
Species 2: Asterales Asteraceae Centaurea americana (American starthistle)
Species 3: Asterales Asteraceae Centaurea solstitialis (yellow starthistle)