Phenology and temperature-dependent development of Ceutorhynchus assimilis, a potential biological control agent for Lepidium draba

Authors: VON VIRAG, ADRIEN - University Of Freiburg; BON, MARIE-CLAUDE - European Biological Control Laboratory (EBCL); CLOSCA, CORNELIA - Commonwealth Agricultural Bureau International (CABI) - Switzerland; DIACONU, ALECU - National Institute Of Research And Development For Food Bioresources; HAYE, TIM - Commonwealth Agricultural Bureau International (CABI) - Switzerland; WEISS, ROSS MICHAEL - Saskatoon Research Center; MULLER-SCHARER, HEINZ - University Of Freiburg; HINZ, HARIET - Commonwealth Agricultural Bureau International (CABI) - Switzerland

Submitted to: Journal of Applied Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/15/2016
Publication Date: 5/1/2016
Citation: Von Virag, A., Bon, M., Closca, C., Diaconu, A., Haye, T., Weiss, R., Muller-Scharer, H., Hinz, H. 2016. Phenology and temperature-dependent development of Ceutorhynchus assimilis, a potential biological control agent for Lepidium draba. Journal of Applied Entomology. DOI: 10.1111/jen.12322.

Interpretive Summary: The heart-podded hoary cress, Lepidium draba (Brassicaceae), is an invasive alien weed that is a major concern for agriculture and biodiversity in the western United States. As current control methods do not provide long-term, sustainable solutions, research has been conducted to find biological control agents. Few populations of an Eurasian weevil, Ceutorhynchus assimilis, were found to develop specifically on the target weed and therefore the weevil is being considered as a potential biocontrol agent. However this weevil species has some populations which are specific to the weed and some which are not. The specific ones are present in southern Europe only, and this raised the question of its ability to survive in colder climates in the target range (North America). Using various temperature dependent parameters to estimate cold hardiness in laboratory in Switzerland and transplant experiments in Romania where the specific ones was relocated , we were able to compare its behavior and phenology to the generalist weevil which occurs in colder climate (like in Romania). Results show that the specific weevil from southern France has the potential to establish in some parts of the target range (e.g. (such as in Washington, Oregon, south-western and north-western Idaho, wide areas of California and Nevada, northern Arizona and parts of Utah).

Technical Abstract: Heart-podded hoary cress (Lepidium draba) is an alien weed that has invaded rangeland in the northwestern USA. A host race (i;e; host-specific biotype) of the weevil, Ceutorhynchus assimilis, is being evaluated as a prospective biological control agent. This biotype is only known from southern Europe, so it is unknown whether it would be adapted to colder climates where the target weed occurs in North America. Populations of the weevil from northern Europe are known to be not specific to the target, and so would not be suitable agents. We investigated the phenology of the weevil in the field in southern France (specialist clade) and Romania (generalist clade) and measured various temperature-dependent parameters in the laboratory. In both regions weevils were univoltine. Oviposition in autumn started later in France compared to Romania, while mature larvae exited galls (to pupate in the soil) earlier the following spring. Weevils transported from France to Romania were able to develop, but their survivorship was lower than Romanian weevils. Mortality of overwintering larvae of both clades increased with decreasing temperature and exposure time. A climate match model (comparing winter temperatures) indicated that the specialist clade of the weevil from France has the potential to establish in some parts of the target range (e.g. Washington, Oregon, south-western and north-western Idaho, wide areas of California and Nevada, northern Arizona and parts of Utah)). However, temperature extremes and winters without snow cover will likely limit its establishment unless rapid adaptive evolution takes place.