Genetica 114: 207–215, 2002. © 2002 Kluwer Academic Publishers. Printed in the Netherlands. 207 Polytene chromosomes of Simulium craigi (Diptera: Simuliidae) Fiona F. Hunter Department of Biological Sciences, Brock University, St. Catharines, Ontario, Canada L2S 3A1 (Phone: 905-688- 5550, ext. 3394; Fax: 905-688-1855; E-mail: hunterf@spartan.ac.brocku.ca) Received 2 February 2001 Accepted 17 November 2001 Key words: clinal variation, cytotaxonomy, polymorphism, polytene chromosomes, Simulium craigi Abstract Simulium craigi Adler and Currie is a polymorphic species based on polytene chromosome banding patterns in the long arm of chromosome III (IIIL). Three cytotypes are described based on the predominant IIIL sequences. These correspond to three broad geographic areas: cytotype ‘CC’ from Pennsylvania; cytotype ‘AF’ from Ontario and Manitoba; and cytotype ‘ACF/BCF’ from New Hampshire. In the absence of sympatric populations, these cytotype differences are best explained by clinal variation within a single species. The relationship of S. craigi to other described members of the S. vernum group is discussed. Introduction In black flies (Simuliidae) the micromorphological features of larval salivary gland polytene chromo- somes have been used extensively to differenti- ate among species, sibling species, and cytotypes. Rothfels (1981) elaborated on the assignment of sib- ling species status through the recognition of sibling- specific autosomal sequences (commonly the result of fixed inversion differences or interchanges), sex chro- mosome differences, and/or autosomal polymorphism profile differences. In the absence of sympatric pop- ulations, the term ‘cytotype’, the more conservative designation, is preferred. There have been several cytological treatments of species in the Simulium vernum Macquart (com- plex) group. The chromosomes of S. vernum s.l. (as Eusimulium vernum) were first studied in detail by Brockhouse (1985). Included in Brockhouse’s 1985 publication are descriptions of 14 S. vernum cyto- types along with descriptions of two closely allied species, S. bicorne Dorogostaisky, Rubtsov, and Vlasenko and S. ‘Yukon’. Adler and Currie (1986) formally described ‘Yukon’ as S. decolletum Adler and Currie. One of Brockhouse’s vernum cytotypes, ‘Cale- don’, was subsequently raised to morphospecies status by Adler and Currie (1986) and is now known as S. caledonense Adler and Currie. Hunter and Connolly (1986) described the chromosomes and presented a working hypothesis for relationships among seven species in the S. vernum group from North Amer- ica. This included S. aestivum Davies, Peterson, and Wood, S. gouldingi Stone, S. croxtoni Nicholson and Mickel, S. fionae Adler (as ‘Simulium sp.’), S. impar Davies, Peterson, and Wood, S. pugetense Dyar and Shannon, and S. quebecense Twinn. Hunter (1987a) characterized four related Western European species: S. carpathicum (Knoz), S. cryophilum (Rubtzov), S. costatum Friederichs, and S. vernum. Adler (1987) described a new species in the group, S. loerchae Adler, found in North America. Reference to the chro- mosomes of S. silvestre (Rubtsov) of the Nearctic region has also been made (Adler, in Currie, 1997). Hunter (1989) examined S. furculatum Shewell, but concluded that it did not belong to the S. vernum species group. The current paper deals with the polytene chromo- some analysis of diverse populations of S. craigi Adler and Currie, a North American species previously de- scribed by Adler and Currie (1986). The objectives are to determine: (1) the taxonomic status of S. craigi given its wide geographic distribution and (2) the relationship of these populations to other described members in the S. vernum group.