Open field host range tests of Ceratapion basicorne (Illiger) (Coleoptera: Apionidae), a candidate for the biological control of Centaurea solstitialis L. Rüstem Hayat 1, Göksel Tozlu 1, Gloria Antonini 2, Carlo Tronci 2, Francesca Lecce 2, Massimo Cristofaro 2, Lincoln Smith 3 1 Ataturk University, Faculty of Agriculture, Plant Protection Department, Erzurum, Turkey, 2 Biotechnology and Biological Control Agency, Via del Bosco, 10, Sacrofano, Italy 3 USDA, Agricultural Research Service, Exotic and Invasive Weeds Research Unit, 800 Buchanan Street, Albany, CA Centaurea solstitialis L. (Yellow starthistle, YST, Fig. 1) is an alien weed native to Southern Europe and Western Asia that has invaded about 9 million hectares of rangeland and pastures in the western U.S.A. In the framework of the search for new biological control agents attacking the weed at early, pre-flowering phenological stages, extensive field surveys were carried out in the Mediterranean basin and Western Asia between 2001 and Among the new potential beneficial insects selected, high priority was given to one Turkish population of the Apionid weevil Ceratapion basicorne (Fig. 2) on the basis of the positive combination of apparently strict host specificity, high infestation rates and damage caused to the host. C. basicorne is an univoltine root-crown boring beetle; females oviposit on young rosettes, larvae develop in the roots causing often important damage to the plant especially when in large number (Fig. 3). Figure 1. C. solstitialis Figure 2. C. basicorne Laboratory host range trials were carried out on the full YST test plant list, including weeds, native North American plants and commercial crop varieties belonging to the Asteraceae family, related to C. solstitialis. Such tests revealed that the weevil, although safe for the majority of the plant tested, was able to develop on two safflower (Carthamus tinctorius L.) commercial varieties in both choice and no-choice conditions. With the objective to assess the real potential risk of a non-target attack of C. basicorne on safflower, open field choice trials were carried out at three locations in the Erzurum Region, Turkey between 2002 and The experiment areas were all characterized by high abundance of wild YST with a C. basicorne infestation rate > 80% (Fig. 4). At each site a 12x6 m field plot was set up. Laboratory-grown potted Yellow starthistle, Turkish and US biotypes plus two commercial safflower varieties (characterized by higher content in oleic and linoleic acid, respectively), were transplanted in the plots in mid April, at the beginning of the oviposition season of C. basicorne. The wild yst population surrounding the field plots was monitored weekly to assess the development status of the weevil population at each site. As soon as the first pupae were found, all test plants were harvested and kept in ventilated bags in laboratory in order to allow adult emergence. Figure 4. Open field choice tests in Turkey and map of plot locations The experiments were carried out at 3 sites (Askale, Cat and Horasan) in 2002, and at 2 sites (Askale and Horasan) in 2003 and Results showed that at two locations the safflower test plants were never attacked by any insect, while at the Askale site, several weevil species emerged from a significant portion of the safflower test plants. Nevertheless, none of such insects was identified as C. basicorne, while almost 100% of the insects recovered from C. solstitialis test plants was identified as C. basicorne (Tab. 1). During the field trials carried out in 2004, molecular techniques were used to identify the immature weevil stages found in test plants upon harvesting. In particular, DNA sequences of the cytochrome C, subunit I (COI) obtained from larvae and pupae found in test plants were compared with the correspondent sequences obtained from identified adults. A sample of 10 immature stages was analyzed for each test plant species/variety allowing to confirm that C. basicorne doesn’t attack safflower, while, again, 100% of the samples from YST were identified as C. basicorne. The results indicate that C. basicorne does not attack safflower under field conditions and that it would not risk damaging this crop if it is introduced to the U.S.A. a Values followed by the same letter in the same row are not significantly different (chi-square test, P < 0.01). b Adults identified: 4 C. scalptum, 1 C. orientale, 2 C. onopordi. c Adults identified: 2 C. scalptum. d Adults identified: C. scalptum, C. orientale. e Adults identified: 8 C. scalptum, 2 C. orientale. Proportion of plants infested (%) a No. Safflower plants Figure 3. C. basicorne damage on YST roots Table 1. Summary of the results of the open field host-range experiments. YST(US)=C. solstitialis US biotype; YST(TR)=C. solstitialis Turkish biotype; Oleic and Linoleic= Commercial safflower varieties.