Field garden experiments to assess the host specificity of Aceria solstitialis (Acari: Eriophyoidea), potential biological control agent for Cen-taurea solstitialis (Asteraceae)

Centaurea solstitialis L. (yellow starthistle) is an annual noxious weed that currently infests millions of acres of rangelands, non-cultivated and natural areas in the Western USA. It displaces native plant communities reducing plant diversity and forage production for livestock and wildlife. Aceria solstitialis L. is an eriophyoid mite found exclusively in association with C. solstitialis in Turkey and Bulgaria. This mite damages bolting plants causing stunting, leaf curling and incomplete flower development. During 2008 and 2009, two open field tests were conducted in Bulgaria, to study the mite’s dispersal behavior and host range. The experiments were conducted on plots of 100 m2 at the experimental field of Agricultural University of Plovdiv. Five plant species were included in the experiment: C. solstitialis (infested and not-infested), C. diffusa Burm.f. .C. cyanus L., Carthamus tinctorius Mohler, Roth, Schmidt & Boudreaux, and Cynara scolymus L. The plants were infested with mites before transplanting them in the field. An infested leaf cutting, with at least 30 mites, was placed on each test plant except on the negative control (C. solstitialis notinfested). Results of these field experiments showed that A. solstitialis mites were present in high population densities only on intentionally infested C. solstitialis and C. cyanus.