Ensuring the Safety of Classical Biological Control for Cabbage Seedpod Weevil in Canada: Assessment of the Ecological Host Range of Candidate Ectoparasitoids in Europe and Clarification of their Taxonomic Status

Abstract

Classical biological control of insect pests and weeds can lead to potential conflicts, particularly if the insect pest and weed agents are closely related. Such a conflict may occur in biological control of the Cabbage Seedpod Weevil (CSPW), Ceutorhynchus obstrictus (Marsham) [=C. assimilis (Paykull); see Colonnelli (2004)] (Coleoptera: Curculionidae), which belongs to the same subfamily, Ceutorhynchinae, as a number of agents introduced or proposed for introduction against invasive alien weed species in North America. The CSPW is a serious pest of canola and rapeseed in North America. Some of the known European parasitoids such as Trichomalus perfectus Walker and Mesopolobus morys Walker (both Hym.; Pteromalidae) show the greatest potential for incorporation into an IPM programme in North America and are currently being considered for introduction. Prior to importation, several issues have to be assessed, and results are presented here: Taxonomy of the European species of the genus Trichomalus and Mesopolobus associated to Ceutorhynchinae hosts were revised and illustrated keys provided to ensure up to date information is available to biological control practitioners. A three years field survey has been carried out in five European countries to field collect Ceutorhynchinae hosts, rear their ectoparasitoids and identify them. Furthermore, implications of the host-parasitoid associations recovered by the surveys are discussed relative to introduction of species to North America for classical biological control of cabbage seedpod weevil.The host specificity of the candidate ectoparasitoids has to be determined in their native cultivated and non-cultivated habitats. A three year field survey has been carried out to document the European parasitoid assemblages associated with several Ceutorhynchinae species either already introduced in North America as classical weed biological control agents (Microplontus edentulus (Schultze) against scentless chamomile, Tripleurospermum perforatum (Mérat) Laínz (=Matricaria perforata Mérat) [Asteraceae]; Hadroplontus litura (Fabricuius) against Canada thistle, Cirsium arvense (L.) Scopoli [Asteraceae]), proposed for introduction (Ceutorhynchus turbatus Schultze against hoary cress, Lepidium draba L. (=Cardaria draba) [Asteraceae]) or of importance in term of conservation (Ceutorhynchus typhae (=C. floralis) (Paykull) on Shepherd s purse, Capsella bursa-pastoris (L.) Medicus [Brassicaceae]). These results are discussed to estimate potential non-target effects on other Ceutorhynchinae species and implications for classical biological control of cabbage seedpod weevil.