Field release of a prospective biological control agent of weeds, Ceratapion basicorne, to evaluate potential risk to a nontarget crop

Ceratapion basicorne is a prospective biological control agent of yellow starthistle (Centaurea solstitialis), which is an invasive alien weed in the USA. Although the weevil has a strong preference for yellow starthistle, it has been reported to develop sometimes on safflower in larval transfer and no-choice experiments. Although safflower was not attacked by this insect in previous field experiments, a release permit was denied because of concern for risk to safflower. Adult C. basicorne were released in a field experiment in which two varieties of safflower were grown in solid blocks on either side of a small number of yellow starthistle plants. Plants were dissected at the time of weevil pupation. Immature insects were reared to adult stage on artificial diet or were preserved in acetone to identify by molecular genetic analysis. C. basicorne infested 54% of the yellow starthistle plants and 0% of 1021 safflower plants. A different weevil, Ceratapion orientale, infested 1.5% of the safflower plants. These results corroborate two other published field studies in which C. basicorne was not reared from safflower. The combined results of nine experiments provide a point estimate that the probability of attack is less than 0.00059, with 99.9% confidence that it is less than 0.0045. 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 in the weevil's native range support the conclusion that this insect poses no significant risk to safflower. Published by Elsevier Inc.