381 On the misidentification of chalcid (Hymenoptera: Chalcidoidea) parasitoids of the cabbage seedpod weevil (Coleoptera: Curculionidae) in North America Gary A.P. Gibson1 Agriculture and Agri-Food Canada, Biodiversity and Integrated Pest Management, K.W. Neatby Building, 960 Carling Avenue, Ottawa, Ontario, Canada K1A 0C6 Hannes Baur Department of Invertebrates, Naturhistorisches Museum, Bernstrasse 15, CH-3005 Bern, Switzerland Bryan Ulmer, Lloyd Dosdall Department of Agricultural, Food and Nutritional Science, 4–10 Agriculture/Forestry Centre, University of Alberta, Edmonton, Alberta, Canada T6G 2P5 Franck Muller CABI Bioscience Centre, Rue des Grillons, Delémont, Switzerland Gibson403 et al. Abstract—Previous identifications in North America of Trichomalus perfectus (Walker, 1835) and Mesopolobus morys (Walker, 1848) (Chalcidoidea: Pteromalidae), the principal chalcid parasitoids of the cabbage seedpod weevil (Ceutorhynchus obstrictus Marsham, 1802) in Europe, are shown to be misidentifications of Trichomalus lucidus (Walker, 1835) and Mesopolobus (Xenocrepis) moryoides sp. nov., respectively. Necremnus duplicatus Gahan, 1941 (Chalcidoidea: Eulophidae) is synonymized formally under Necremnus tidius (Walker, 1839) syn. nov., confirm- ing a previous, tentative synonymy. Both sexes of N. tidius, M. moryoides, and T. lucidus are il- lustrated and compared with those of similar species using macrophotography and scanning electron microphotography. Hypotheses are offered to explain why the principal chalcid parasitoids of the cabbage seedpod weevil differ between North America and Europe and how the three treated species came to be in North America. Résumé—Les insectes connus jusqu’ici en Amérique du Nord comme Trichomalus perfectus (Walker, 1835) et Mesopolobus morys (Walker, 1848) (Chalidoidea : Pteromalidae), les princi- paux chalcidiens parasitoïdes du charaçon de la graine de chou (Ceutorhynchus obstrictus Mars- ham, 1802) en Europe, sont mal identifiés; il s’agit, en fait, respectivement de Trichomalus lucidus (Walker, 1835) et de Mesopolobus (Xenocrepis) moryoides sp. nov. Necremnus duplica- tus Gahan, 1941 (Chalcidoidea : Eulophidae) devient formellement un synonyme plus récent de Necremnus tidius (Walker, 1839) syn. nov., confirmant ainsi une synonymie préliminaire anté- rieure. Des macrophotographies et des microphotographies au microscope électronique à ba- layage viennent illustrer les deux sexes de N. tidius,deM. moryoides et de T. lucidus et permettent des comparaisons avec les espèces similaires. Des hypothèses cherchent à expliquer pourquoi les chalcidiens parasitoïdes du charançon de la graine de chou sont différents en Amé- rique du Nord et en Europe et comment les trois espèces en question se sont retrouvées en Amé- rique du Nord. [Traduit par la Rédaction] Introduction The cabbage seedpod weevil, Ceutorhynchus Received 18 January 2005. Accepted 13 May 2005. obstrictus Marsham, 1802 (= C. assimilis 1Corresponding author (e-mail: [email protected]). (Paykull, 1792)) (Coleoptera: Curculionidae), Can. Entomol. 137: 381–403 (2005) © 2005 Entomological Society of Canada 382 Can. Entomol. Vol. 137, 2005 was introduced from Europe to western North synonymized T. fasciatus under Trichomalus America about 70 years ago. Its host range in- lucidus (Walker, 1835), and Delucchi and Gra- cludes plants of the family Brassicaceae. The ham (1956) stated that all literature records re- weevil initially was a pest of mustard, cabbage, ferring to T. fasciatus as a parasitoid of turnip, rutabaga, and Brussels sprouts (Brassica C. obstrictus probably were based on misidenti- spp.) grown for seed (Hanson et al. 1948; fications of Trichomalus perfectus (Walker, Carlson et al. 1951; Walz 1957). Since its intro- 1835). Using the description of T. perfectus duction it has become an invasive pest through- provided by Delucchi and Graham (1956), Peck out much of North America north of Mexico (1963) identified individuals of a Trichomalus (Brodeur et al. 2001; Cárcamo et al. 2001; Ma- species reared from C. obstrictus in British Co- son et al. 2004) and a major economic pest of lumbia as T. perfectus. Ever since then, this brassicaceous oilseed crops including canola name has been used for the Trichomalus spe- and rape (Brassica napus L. and B. rapa L.) cies parasitizing C. obstrictus in western North (Buntin et al. 1995; Dosdall et al. 2001). America. It was also used by Buntin (1998) for The first documented presence of parasitoids reared from the seedpods of C. obstrictus in North America was from adults B. napus in Georgia, United States of America, collected in 1931 in Vancouver, British Colum- the only locality in eastern North America for bia, Canada (Hanson et al. 1948). Baker (1936) which parasitoids of C. obstrictus have been re- subsequently reared specimens from mustard ported. seedpods in Washington State, United States of The species identified as M. morys and America, along with four hymenopterous T. perfectus were not reported in North America parasitoids that were stated to represent at least prior to being reared from C. obstrictus soon two distinct groups. Although these specimens after the first recorded occurrence of this wee- were not identified and have not been located, vil. Therefore, it has long been assumed that later rearings indicate they undoubtedly were both the parasitoid species and C. obstrictus chalcids. Gahan (1941) described parasitoids were introduced together in seed shipments reared from C. obstrictus in turnip seedpods (Hanson et al. 1948; McLeod 1953). collected in Washington in 1937 as a new spe- Trichomalus perfectus and M. morys are the cies, Necremnus duplicatus (Eulophidae). In ad- principal chalcid parasitoids of C. obstrictus in dition to the reared series, Gahan also had Europe, where parasitism rates typically exceed several specimens that he did not include in the 50%, can reach 90%, and can be high even at type series but which he stated seemed to be the low pest densities (Buntin 1998; Murchie and same species, including two individuals from Williams 1998). Trichomalus perfectus, the Netherlands reared from Brassicaceae pods. M. morys, and N. duplicatus have been reported Bou ek (1959) later suggested that as the most important parasitoids of N. duplicatus is very near, if not identical, to C. obstrictus in North America (Kuhlmann et the European species Necremnus tidius (Walker, al. 2002), but parasitism rates are generally 1839). Two other chalcid species were also much lower than those found in Europe reared from C. obstrictus soon after its initial (Harmon and McCaffrey 1997; Buntin 1998). discovery in Washington and subsequently In their review of the scientific literature re- identified as European species. Doucette (1944) lating to parasitoids of the cabbage seedpod reared an unidentified species of Amblymerus weevil, Murchie and Williams (1998, p. 165) Walker, which was identified as Disema sp. in stated that “the study of literature is hampered Doucette (1948), Xenocrepis sp. in Hanson et by synonymy and misidentification”. During al. (1948), and Xenocrepis pura Mayr in Walz the course of identifying chalcid parasitoids of (1957). These names are now recognized as ju- the cabbage seedpod weevil in western Canada, nior synonyms of Mesopolobus Westwood we confirmed that N. duplicatus is a junior syn- (1833) and Mesopolobus morys (Walker, 1848) onym of N. tidius, as has long been speculated. (Pteromalidae), respectively (Graham 1957). We also discovered that the species reported in Both Doucette (1944) and Breakey et al. (1944) the North American literature as T. perfectus also reared a species initially identified as and M. morys have been consistently misidenti- Trichomalus fasciatus (Thomson, 1878) fied. The species identified as T. perfectus is (Pteromalidae), which was a previously known T. lucidus, which is reported as a principal parasitoid of C. obstrictus in Europe (Heymons parasitoid of Ceutorhynchus alliariae Brisout, 1921). However, Graham (1956) subsequently 1860 and Ceutorhynchus roberti Gyllenhal, © 2005 Entomological Society of Canada Gibson et al. 383 1837 in Switzerland but is not known to be a UGCA University of Georgia Museum of common parasitoid of C. obstrictus in Europe Natural History, Athens, Georgia, (Klander 2001; Muller et al. 2004). The species United States of America identified as M. morys represents a new species USNM United States National Museum of of uncertain area of origin. In this paper we de- Natural History, Washington, District scribe the new Mesopolobus species and differ- of Columbia, United States of Amer- entiate its dimorphic sexes from those of ica similar European species, provide features to WFBM William F. Barr Entomological Mu- differentiate T. lucidus from T. perfectus, and seum, University of Idaho, Moscow, formalize the synonymy of N. duplicatus under Idaho, United States of America N. tidius. This is done to clarify the nomencla- WFIC Western Forest Insect Collection, ture and to provide evidence that North Amer- Corvallis, Oregon, United States of ica lacks all the principal chalcid biological America control agents of C. obstrictus found on canola in Europe. Our initial concepts of European Mesopolobus and Trichomalus were based on Graham (1969), of European Necremnus on Materials and methods Bou ek (1959) and Graham (1959), and of This study is based on voucher specimens of Nearctic Necremnus on Gahan (1941). Type species previously reported in the literature as material of the senior synonym of putative spe- reared