Ceratapion basicorne (Illiger) (Coleoptera: Curculionidae): biosaggi di laboratorio e campo per valutarne la specificità fisiologica come agente di controllo di Centaurea solstitialis l. (Asteraceae: Cardueae)

Ceratapion basicorne (Illiger) (Coleoptera: Curculionidae): laboratory and open field trials to assess its specificity as biocontrol agent of Centaurea solstitialis (Asteraceae: Cardueae). Prospective biological control agents generally must be demonstrated to not pose risks to non-target plants. Laboratory experiments evaluating host plant specificity are the most common method of evaluating such risk; however, they are constrained by limitations of space and number of replicates, giving sometimes unclear results. Field experiments in the land of origin of the prospective agent can provide more realistic conditions. The root boring weevil Ceratapion basicorne normally oviposits in the leaves of young yellow starthistle (Centaurea solstitialis) plants, and larvae develop inside the root crown and pupate inside the plant. Despite the high specificity showed for the target weed by the weevil, during its screening as biological control agent for yellow starthistle, a permit application to release it in the U.S.A. was denied in 2006 because of the risk it could be dangerous to safflower (Carthamus tinctorius): in fact, this weevil, has been reported to develop occasionally on the non-target plant in laboratory no-choice experiments. The main concern was related to the economic importance of safflower, hypothesizing that the number of replicate plants in the previous experiments was still too small. When a small risk is perceived for a very abundant plant, such as a crop, larger scale experiments are needed to improve confidence in the results. For this reason, an additional open field test was set up in Rome, releasing adults of C. basicorne in a field experiment in which two varieties of safflower were grown in solid blocks near a small number of yellow starthistle plants. The weevil infested 54% of the yellow starthistle plants, while no individuals of C. basicorne were reared from 1021 safflower plants. Additional testing could not reduce this probability to zero; however, the consistency of results from field experiments in three countries and the absence of any report of this insect being reared from safflower in the field support the conclusion that this weevil species poses no significant risk to safflower.