The status of Rhinusa antirrhini, a biocontrol agent for toadflax (Linaria) in BC, has been changed from primary (the responsibility of the Forest Practices Branch) to secondary (the responsibility of Range branch) to be used now as a tool to control its target invasive plants.
There are three invasive alien Linaria species of concern in BC, Dalmatian toadflax (L. dalmatica (L.) P. Mill. ssp. dalmatica), yellow toadflax (Linaria vulgaris (L.) P. Mill.) and broomleaf toadflax, often referred to as narrow-leaved Dalmatian toadflax, (Linaria genistifolia (L.) P. Mill.) (http://plants.usda.gov). Of these, Dalmatian toadflax is the most widespread, followed by yellow and then narrow-leaved toadflax, the latter being scarce in the province. All three perennial species were introduced from Europe as ornamentals and have since naturalized in North America (Groppe 1992). For example, Dalmatian toadflax was introduced as an ornamental in the USA in 1894 (Robocker 1974). These toadflax species are difficult to control manually or with herbicide due to the creeping root systems and waxy cuticles. Biological control, therefore, was sought to control these species.
Efforts to acquire biological control agents for BC Dalmatian and yellow toadflaxes began in the 1960s (De Clerck-Floate and Harris 2002). Most agents attack both yellow and Dalmatian toadflaxes as well as broomleaf toadflax, the latter two plant species being closely related, but the agents generally have host plant preferences dependent on which plant species they were originally harvested from in Europe (i.e., they have formed ‘host races’). Since the 1960’s, five agents have been purposely released into BC while an additional three were adventive, (i.e. have arrived in North America unintentionally). Although originally adventive in North America – recorded in 1909 in Massachusetts, USA and in 1917 in Montreal, Quebec (Smith 1959) - Rhinusa antirrhini (seed-feeding weevil) was subsequently screened (1989 to 1992) and purposely released into BC in 1993. Following inspection in a federal quarantine facility, the weevils were released into propagation tents by the MFR.
There are two strains of Rhinusa antirrhini in BC. One strain of weevil is specific to yellow toadflax and another is specific to Dalmatian toadflax (Powell et al. 1994). The Dalmatian toadflax strain of R. antirrhini from Yugoslavia, which was screened and released in BC in 1993, (De Clerck-Floate and Harris 2002) established first in tents and subsequently in field releases. Often little is known about the habitat requirements of new agents when compared to available habitat details from the agent’s native country.
Following confirmed establishment, the weevils were collected and moved into increasingly diverse habitat regimes in order to test their limitations and they have been found to readily increase in various populations of Dalmatian toadflax in BC. The weevils have been propagated, their establishment and habitat requirements have been studied and handling requirements have been investigated in order to provide invasive plant managers with a useful treatment tool against target invasive alien plants.
De Clerck-Floate, R.A. and P. Harris. 2002. Linaria dalmatica (L.) Miller, Dalmatian toadflax (Scrophulariaceae). In Biological Control Programmes in Canada, 1981-2000, Mason, P.G., J.T. Huber. (eds). CAB International, Oxon, UK: 368-374.
Gassmann, A., Tosevski, I., Spiewak, E., Heinlein, G., Recher, H., Yaworski, K., and Thalmann M. 2001. Biological control of toadflaxes, Linaria spp. Annual report 2001. CABI Bioscience, Switzerland Centre, Delemont, Switzerland. 25p.
Groppe, K. 1992. Final report Gymnetron antirrhini Paykull (Col.: Curculionidae). A candidate for biological control of Dalmatian toadflax in North America. CAB IIBC European Station, Delemont, Switzerland. 22p.
Harris, P. 1961. Control of toadflax by Brachypterolus pulicarius (L.) (Coleoptera: Nitidulidae) and Gymnaetron antirrhini (Payk.) (Coleoptera: Curculionidae) in Canada. 93:977-981.
Powell G., A. Sturko, B. Wikeem and P. Harris. 1994. Field Guide to the Biological Control of Invasive plants in British Columbia. Land Management Handbook Number 27. B.C. Min. For.,Res. Br.
Robocker, W.C. 1974. Life history, ecology, and control of Dalmatian toadflax. Wash. Agric. Exper.Station, Wash. State Univer. 20p.
Smith, J. Morris. 1959. Notes on insects, especially Gymnaetron spp. (Coleoptera:Curculionidae), associated with toadflax, Linaria vulgaris Mill. (Scrophulariaceae), in North America. Can. Entomol. Vol. XCI, No.2: 116-121.