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J. ENTOMOL. SOC. BRIT. COLUMBIA 101, DECEMBER 2004 131 Lestes disjunctus Selys and L. forcipatus Rambur (Odonata: Lestidae): Some Solutions for Identification JOHN P. SIMAIKA1 and ROBERT A. CANNINGS2,3 ABSTRACT Five species of the damselfly genus Lestes live in British Columbia, Canada, and of these, Lestes forcipatus Rambur and L. disjunctus Selys are the most similar and most difficult to separate morphologically. Females can be readily distinguished by the size of the ovipositor, but males are difficult to separate. In British Columbia, L. disjunctus is the more common, widespread and familiar species. Before 1998, L. forcipatus specimens were mistaken for those of L. disjunctus because the former is primarily an eastern North American species and because most Lestes species are usually identified using male characters. With the discovery that L. forcipatus is part of the western fauna, an evaluation of the relative status of the two species in British Columbia is necessary. The best method for separating the two species uses the length of the anterior lamina (part of the secondary genitalia) as a unique character or as part of ratios using other measurements. In addition, in at least western North America, L. forcipatus males are more pruinescent than those of L. disjunctus, especially on the thorax. Identification using the pruinescence pattern was tested in the field and is recommended as a simple and accurate method for western North America. Soaking Odonata specimens in acetone, a common technique used to preserve colours, damages surface pruinescence and should not be used to preserve mature, pruinescent adults, including those of Lestes species. To identify L disjunctus and L. forcipatus males treated in acetone, it may be necessary to calculate ratios based on various character measurements. Future research should inves- tigate spatial and temporal differences between the species, as well as modes of inter- specific communication. Key Words: Odonata, Lestes forcipatus, Lestes disjunctus, identification, British Co- lumbia, pruinescence, acetone, anterior lamina. INTRODUCTION Five species of the damselfly genus standing water habitats with abundant Lestes (Odonata: Zygoptera: Lestidae) aquatic vegetation and, in southern BC, occur in British Columbia (BC), Canada: adults fly from mid-June to mid-October L. congener Hagen (Spotted Spreadwing), (Cannings 2002). L. disjunctus Selys (Northern Spreadwing), L. forcipatus is generally much less L. dryas Kirby (Emerald Spreadwing), L. common than L. disjunctus, although it is forcipatus Rambur (Sweetflag Spread- as abundant in some cold fen habitats, and wing), and L. unguiculatus Hagen (Lyre- both species often occur at the same site. L. tipped Spreadwing). L. disjunctus is the forcipatus does not range as far north as L. most common, widespread and familiar disjunctus and, although not known from Lestes species in the province, and one of much of BC’s north, it has been collected the most abundant odonates in Canada, in the southeastern Yukon. In the western ranging as far north as the Arctic treeline Canadian Cordillera, it is most common in (Cannings 2002). It inhabits many types of sedge fens (Cannings 2002). Walker 1 #402-1063 Foul Bay Road, Victoria, British Columbia, Canada V8S 4J3 2 Royal British Columbia Museum, 675 Belleville Street, Victoria, British Columbia, Canada V8W 9W2 3 Author to whom correspondence should be sent 132 J. ENTOMOL. SOC. BRIT. COLUMBIA 101, DECEMBER 2004 (1953) described L. forcipatus habitat in females. In L. forcipatus females the ovi- Ontario as "ponds, both temporary and positor valves reach the tips of the cerci; in permanent, marshy lakes, and slow, weedy L. disjunctus they do not (Walker 1953, streams". In BC L. forcipatus has been Cannings 2002) (Fig. 1). collected from mid-June to mid-September Lestes species are usually brown, black, (Cannings 2002). metallic green or bronze above and mostly L. forcipatus was not reported in BC pale below; especially in males, the head, until 1998, when it was first collected in thorax, base and tip of abdomen become the Rocky Mountain Trench north of pruinescent bluish white with age. Pruines- Golden and subsequently found in many cence (pruinosity) is a waxy substance other localities in the southeastern part of produced by the hypodermis in many the province. However, it probably has groups of Odonata and excreted on the long been a resident of the province; it was cuticular surface through porous canals long overlooked because of its close re- (Gorb 1994). Pruinescence is implicated in semblance to L. disjunctus (Ramsay and thermal regulation in dragonflies (Garrison Cannings 2000). Before 1998, L. forci- 1976, Paulson 1983) and is thought to play patus was not known west of Saskatche- a role in species recognition and intraspeci- wan (Walker 1953, Westfall and May fic communication -- indeed, the patterns 1996), and had just recently been found in of pruinescence in males may be a result of Washington State, the first record west of sexual selection (Jacobs 1955, Corbet Montana (Ramsay and Cannings 2000). 1999). Therefore, pruinescence patterns The species is now known from seven might offer good species identification counties in that state and one in Idaho characters, especially in males. (Paulson 2004). By 1999 L. forcipatus had The object of this project was to find been discovered at several other BC loca- novel and definitive distinguishing charac- tions farther south and west, and by 2000 teristics between males of L. disjunctus had been collected on Vancouver Island. and L. forcipatus, building on the studies Some of our old museum specimens of L. of workers in eastern North America. disjunctus from many regions of the prov- Thus, we hope (a) to distinguish males in ince have been re-identified as L. forci- the absence of associated females; (b) to patus, indicating that museum collections identify, with relative ease, the species in across western Canada probably contain the field, (c) to correct any misidentifica- many misidentified specimens. tions of specimens in BC museum collec- Males of L. disjunctus and L. forcipatus tions; and (d) to establish accurate distribu- are difficult to separate, although numer- tions for both species in BC. The first part ous characters have been employed in of the present work measures certain struc- identification (Walker 1953, Westfall and tures of the male genitalia to find the best May 1996, Catling 2002, Donnelly 2003). features to separate the species. The sec- The usual method of distinguishing the two ond part quantifies the degree of pruines- species and confirming their presence at a cence of adult males of each species. location is through identification of the MATERIALS AND METHODS Specimens. We measured 50 male L. dis- rowed from the Spencer Entomological junctus and 45 male L. forcipatus speci- Museum, UBC, Vancouver, and the Slater mens from localities in BC and Alberta Museum of Natural History, Tacoma, WA. (two L. disjunctus only from Alberta) and A list of the specimens and their collection from Washington and Maine in the United data is on file at the RBCM and is avail- States. Eighty-four of the specimens were able on request. Most specimens were in from the Royal British Columbia Museum copula or in tandem, except for three L. (RBCM), Victoria; the others were bor- forcipatus and one L. disjunctus; thus, the J. ENTOMOL. SOC. BRIT. COLUMBIA 101, DECEMBER 2004 133 Figure 1. Lateral view of apex of female abdomen. Top, Lestes disjunctus; Bottom, L. forcipatus. OV = ovipositor. identities of almost all males were con- sperm vesicle (MS) (penis vesicle of Cat- firmed using the associated females. ling (2002) and Donnelly (2003)). Measurements. During examination, each 6. Length of penis shaft (PS). specimen was held by the base of the 7. Length of sperm vesicle (SV). wings using a small padded alligator clamp Apex of abdominal segment 10 (Fig. 4): soldered to a #7 insect pin. The pin was 8. Height of apical hood (HT). This inserted into a cork mount, and the speci- structure is a triangular projection on the men held in a standardized measuring posi- dorsal apex of abdominal segment 10. The tion. Specimens were examined at 100x apex of the abdomen was viewed end-on. magnification and measurements were 9. Width of base of apical hood (HL). made to 0.01 mm. 10. Width of the abdomen (WA). The Thirteen characters were measured; greatest width of the abdomen measured terminology follows Westfall and May when the apex of the abdomen was viewed (1996) and Donnelly (2003). end-on. Cercus (Fig. 2): Other: 1. Distance from base of apical tooth to 11. Length of abdominal segment 2 base of basal tooth (AB). (S2). Measured in lateral view. 2. Distance from apex of cercus to base 12. Length of abdominal segment 3 of apical tooth (AC). (S3). Measured in lateral view. 3. Distance from swelling at medial 13. Width of head (HD). The distance base of cercus to base of basal tooth (BB) between the extreme lateral edges of the (not figured). eyes, measured dorsally. Secondary genitalia (abdominal segment We analysed the difference between 2) (Fig. 3): species for each character measured using 4. Length of the anterior lamina a z-test after checking for uniformity of (anterior hamule) (AL). Walker (1952, variance, using the MS Excel Data Analy- 1953) did not explain how to measure the sis Tool (Stinson and Dodge 2004). lamina, but Catling (2002) and Donnelly Pruinescence. (2003) prefer to measure the ventral length Pterothorax (Fig. 5). We compared the of the hamule from where it appears from extent of pruinescence on the head, ptero- above sternite 1. He notes, however, that thorax (fused mesothorax and metathorax), specimens show different degrees of bend- and abdominal segments 1 to 10 between ing in abdominal segments 1 and 2 and males of the two species.

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