J. Appl. Entomol. 130(8), 401–409 (2006) doi: 10.1111/j.1439-0418.2006.01085.x Ó 2006 Agric. & Agri-Food Canada Journal compilation Ó 2006 Blackwell Verlag, Berlin Importance of long-term research in classical biological control: an analytical review of a release against the cabbage seedpod weevil in North America D. R. Gillespie1, P. G. Mason2, L. M. Dosdall3, P. Bouchard2 and G. A. P. Gibson2 1Agriculture and Agri-Food Canada, Research Centre, Agassiz, British Columbia; 2Agriculture and Agri-Food Canada, Research Centre, Ottawa, Ontario; 3Department of Agricultural, Food and Nutritional Science, University of Alberta, Edmonton, Alberta, Canada Ms. received: April 18, 2006; accepted: July 3, 2006 Abstract: Cabbage seedpod weevil, Ceutorhynchus obstrictus (Marsham) (Col., Curculionidae), is an invasive alien pest that is spreading in North America. To aid with planning for introductions of European parasitoids in North America, we examined the status of the only classical biological control release against this pest in North America, which in 1949 introduced Mesopolobus morys, Stenomalina gracilis and Trichomalus perfectus (Hym., Pteromalidae). Weevils and parasitoids were reared in 2005 from mass collections of seedpods of Brassica napus, Brassica rapa and Raphanus raphanistrum (Brassicaceae) from 18 sites in the Fraser Valley, near Vancouver, British Columbia, Canada. Of the three European parasitoid species that were originally released, only S. gracilis was found. The predominant hymenopterous parasitoid species were Trichomalus lucidus, S. gracilis, Mesopolobus moryoides (Pteromalidae), Necremnus tidius (Eulophidae) and Eupelmus vesicularis (Eupelmidae). These constituted over 97% of the parasitoids reared, although overall parasitism was low. Only M. moryoides is clearly North American in distribution; other than S. gracilis, the remaining species were either accidentally introduced or are Holarctic in distribution. Based on these results, re-releases of M. morys and T. perfectus in North America should be considered as part of a classical biological control programme. However, redistribution of S. gracilis is not recommended at present because of potential conflicts with biological control programmes against weeds. Ongoing re-examination of classical biological control programmes can further our understanding of failure of release programmes, particularly when re-examination can be made in the light of improved taxonomy and systematics of the target and agent species. Key words: Ceutorhynchus assimilis, Stenomalina gracilis, cabbage seedpod weevil, Ceutorhynchinae, classical biological control, parasitoids, Pteromalidae 1 Introduction why failures have occurred and so improve future chances for success in biological control (Hopper Biological control has provided important solutions to 2001). invasions of alien insect pest species in agricultural and Cabbage seedpod weevil, Ceutorhynchus obstrictus forest ecosystems since formal programmes were (Marsham) [C. assimilis (Paykull); see Colonnelli 1990, implemented more than 100 years ago. The ecological 1993], an invasive species of European origin, is a basis of classical biological control is to reconstruct the serious pest of canola and rapeseed (Brassica napus L. natural enemy complexes of non-indigenous plant or and Brassica rapa L.) in North America (McCaffrey arthropod species that have become pests in regions 1992; Buntin et al. 1995; Ca´rcamo et al. 2001; Dosdall where they have been accidentally introduced (Mills et al. 2002; Mason et al. 2004). Economic losses result 1994). Despite the many successes in biological con- from adult feeding on flower buds (bud-blasting) and trol, a great number of releases have failed in one way larvae feeding within seedpods (McCaffrey et al. 1986; or another (Turnbull and Chant 1961; Beirne 1975; Buntin and Raymer 1994). The weevil was first Van Driesche and Bellows 1996). Long-term studies of recorded in North America in 1931 at the port city the fate of classical biological control releases are of Vancouver, British Columbia (McLeod 1962), and almost universally recommended as a way to record has since spread to other parts of western and eastern and understand both the successes and failures, but North America (Baker 1936; Hagen 1946; Crowell such studies are rarely accomplished in practice. In the 1952; Walz 1957; Anonymous 1977; Dolinski 1979; absence of such long-term studies, retrospective ana- Boyd and Lentz 1994; Buntin et al. 1995; Brodeur lyses can be useful to better understand the reasons et al. 2001; Ca´rcamo et al. 2001; Dosdall et al. 2002; 402 D. R. Gillespie et al. Mason et al. 2004). It was not discovered in Alberta The discovery that T. perfectus and M. morys had in until 1995, but based on surveys conducted from 1997 fact been released in British Columbia in 1949 (Gibson to 2000, Dosdall et al. (2002) determined that it was et al. 2006a), but had never been reared from surveys dispersing at the rate of approximately 55 km per year. in western and south-eastern United States (Gibson As a result, they predicted that C. obstrictus will et al. 2005, 2006b), indicated the need for a new survey eventually establish itself throughout the entire canola- to determine whether or not either species had estab- growing region of western Canada. Furthermore, lished and is now present in British Columbia. Olfert and Weiss (2006) predicted that, with increases Trichomalus perfectus, M. morys and S. gracilis were in temperature because of climate change, the risks released in British Columbia near Dewdney and Sardis associated with C. obstrictus will become more severe in the lower Fraser Valley (McLeod 1951). Definitive in areas it presently occupies, and it will be able to information concerning their presence or absence in establish in new localities. Consequently, Brassica British Columbia would most likely be obtained industries, particularly those producing seed crops, through surveys in the area where they were first will increasingly risk damage by this pest. The only introduced. If either or both species could not be control measure currently available to producers is the found, then introductions could be considered (Kuhl- application of broad-spectrum chemical insecticides mann et al. 2002). If either or both species were (Dosdall et al. 2001). In Europe, where the North present, then populations could be redistributed into American weevil populations originated (Laffin et al. areas where C. obstrictus has more recently dispersed 2005), natural enemies provide control (Murchie 1996; and is causing extensive economic damage. Williams 2003). Thus, management strategies that The classical biological control release against C. include classical biological control should be pursued obstrictus was regarded as a Ôpartial successÕ by in North America. McLeod (1962) and Munroe (1971). Evaluation of The only attempt at classical biological control of C. the fate of the 1949 releases has gained new urgency in obstrictus in North America was the release of three the light of the extensive economic losses to western species of pteromalid larval ectoparasitoids in British Canadian canola production that are attributable to C. Columbia, Canada in 1949. These species were reported obstrictus infestations (Dosdall et al. 2001). As part of as Habrocytus sp. (Pteromalus sp.), Trichomalus fasci- a larger retrospective analysis of cabbage seedpod atus (Thomson) [Trichomalus lucidus (Walker)] and weevil biological control in North America, our Xenocrepis pura Mayr [Mesopolobus morys (Walker)] objectives were to survey populations of C. obstrictus (Hym., Pteromalidae) (Anonymous 1949). It was not in the Fraser Valley in order to clarify the presence of until over 50 years later that voucher material of the T. perfectus and M. morys in British Columbia and to introduced species was critically re-examined to sub- document the host plant and parasitoid associations stantiate their identity. The identification of M. morys that have evolved over the 70 years since C. obstrictus was confirmed but it was determined that T. lucidus and was introduced. Habrocytus sp. were misidentifications of Trichomalus perfectus (Walker) and Stenomalina gracilis (Walker) (Pteromalidae), respectively (Gibson et al. 2006a). 2 Materials and Methods Several studies have reported parasitoids reared from C. obstrictus in North America (Baker 1936; Collections were made among Brassicaceae plants at 18 sites Gahan 1941; Breakey et al. 1944; Doucette 1944, 1948; in the Fraser Valley of British Columbia (table 1, fig. 1). Hanson et al. 1948; McLeod 1953; Walz 1957; Har- Adult weevils collected from sweep-net samples made at the mon and McCaffrey 1997; Buntin 1998). Reported 18 sites were sorted and stored in 70% ethanol. We were parasitoids include Microctonus melanopus Ruthe unable to make collections at all sites on each sample date because of disruptions from mowing and other agricultural (Hym., Braconidae), and specimens identified as T. operations. Timing of attack by weevils and parasitoids was perfectus and M. morys. All three of these species are estimated from eight sites (sites 3, 7, 8, 10, 17, 22, 25, 27) important regulators of C. obstrictus populations in where it was possible to make collections throughout the Europe (Crowell 1952; Bonnemaison 1957; Jourdheuil period when weevils were present. Site 3 was located at a rail 1960; Laborius 1972; Lerin 1987; Bu¨ chi 1991, 1993; crossing where B. napus was growing in gravel on the edge of Murchie 1996; Williams 2003).