354 Florida Entomologist 89(3) September 2006 VARIABILITY IN LARVAL CHARACTER STATES USED TO DISTINGUISH BETWEEN SPECIES OF PANTALA HAGEN (ODONATA: LIBELLULIDAE) BRETT H. P. LANDWER AND ROBERT W. SITES Enns Entomology Museum, Division of Plant Sciences, University of Missouri, Columbia, Missouri 65211, U.S.A. (e-mail: [email protected] and [email protected]) ABSTRACT Despite widespread distributions and abundance, previously published diagnoses of the lar- vae of the two species of the dragonfly genus Pantala often were contradictory or confusing. Morphometric analysis of mensural characters and qualitative analysis of relative character states were used to determine the ability of previously published characterizations to accu- rately distinguish larvae of the two species. We found that many published characterizations were inaccurate or insufficient, and their use in making species level determinations would result in frequent misidentifications. In distinguishing between the two species, the most useful and reliable characteristic was the palpal setal count. However, in specimens where this count is intermediate, other characteristics may need to be evaluated. RESUMEN A pesar de su distribución amplia y su abundancia, las diagnosis publicadas anteriormente de las larvas de dos especies de libélulas del género Pantala a menudo son contradictorias o confusas. El análisis morfométrico de los carácteres mensurales y el análisis cualitativo de los carácteres de estado relativos fueron empleados para determinar la abilidad de las ca- racterizaciones publicadas anteriormente para distinguir las larvas de las dos especies con exactitud. Nosotros encontramos que muchas de las caracterizaciones publicadas fueron inexactas o insuficientes, y su uso para hacer determinaciones a nivel de especie resultarían frecuentemente en identificaciones equivocadas. Para distinguir entre las dos especies, la ca- racterística mas útil y confiable es el conteo de las setas del palpo. Sin embargo, en especi- menes donde el conteo es intermedio, se necesitan que otras características sean evaluadas. The genus Pantala Hagen is represented However, authors continued to characterize the worldwide by two species, both of which are wide- movable hook of P. hymenaea as 2 times as long as spread and abundant in the United States. Many the crenulations of the labial palp while charac- characters have been used to diagnose the larva of terizing that of P. flavescens as less (Byers 1930; each species and distinguish between them. How- Smith & Pritchard 1956; Walker & Corbet 1975; ever, character states attributed to each species Huggins & Brigham 1982). frequently have been contradictory among au- Two of the interspecific distinctions that appear thors, raising questions as to the diagnostic reli- most commonly in the modern literature without ability of these characters. contradiction were first given by Musser (1962), Kennedy (1923) was the first to distinguish be- who stated that the lateral spines of abdominal seg- tween P. hymenaea (Say) and P. flavescens (Fabri- ment IX were less than three times as long as the cius). Needham (1901) had previously character- basal width in P. hymenaea, and at least three times ized the movable hook of P. flavescens as “hardly as long in P. flavescens. Musser also mentioned a longer than the teeth.” Kennedy described the “slight hump midway along” the dorsal margin of larva of P. hymenaea and distinguished it from the epiproct, and diagrammed the dorsal margin Needham’s diagnosis of P. flavescens on the basis abruptly decurved at a point somewhat beyond of the moveable hook of the former as “twice as midlength in P. hymenaea, while characterizing and long as the crenulations of the distal edge of the depicting a straight dorsal margin of the epiproct in lobe.” Lamb (1929) investigated this character P. flavescens. Both of these distinctions subse- and found that the mean ratio of the length of the quently have been repeated, and the accompanying movable hook to length of the first palpal crenula- diagrams reproduced, in several faunistic treat- tion was 2.2 in P. hymenaea (3 specimens, 1 ments (e.g., Walker & Corbet 1975; Huggins & reared) and 2.6 in P. flavescens (8 reared speci- Brigham 1982; Needham et al. 2000). Paulson mens). Musser (1962) examined more specimens (1966) also noted that the lateral spines of P. flave- than the previous authors (60 P. hymenaea, 1 with scens were more elongate than those of P. hymenaea associated adult; 39 P. flavescens, 3 with associ- but offered no quantification other than that the ated adults) and found the ratios to be 2.0 and 2.5- spines of VIII reach or exceed the apical margin of 3.0 for P. hymenaea and P. flavescens, respectively. IX in the former and not the latter. Landwer & Sites: Larval Characters to Distinguish Pantala species 355 Palpal setal counts also have been used to were measured on one side of the specimen, along characterize each species of Pantala and to distin- a line parallel to the long axis of the body, from the guish between them. P. flavescens is generally posterior margin of the segment immediately ad- characterized as bearing 12-14 palpal setae jacent to the base of the spine to the level attained (Needham 1901; Lamb 1929; Needham & Hey- by the tip of the spine. The basal width of a lateral wood 1929; Byers 1930; Klots 1932; Smith & Prit- spine was measured along a tangent perpendicu- chard 1956; Musser 1962; Walker & Corbet 1975; lar to the long axis of the body, from the point on Huggins & Brigham 1982) and P. hymenaea as the posterior margin of the segment immediately bearing 15 (Kennedy 1923; Needham & Heywood adjacent to the base of the spine to the lateral 1929; Byers 1930; Klots 1932; Smith & Pritchard margin of the segment. Mid-dorsal segment 1956; Musser 1962; Walker & Corbet 1975; Hug- length was measured from the anterior to the pos- gins & Brigham 1982) or more (Lamb 1929; Klots terior margin of the tergite. Palpal setae were 1932; Musser 1962). Paulson’s (1966) table of pal- counted on each palp. pal setal counts is the only work documenting in- Other characteristics were evaluated qualita- traspecific variation and, in P. flavescens, he found tively. Specimens were examined in lateral view 14 or fewer setae on at least one palp in all 16 to determine if the apex of the epiproct exceeded specimens examined (4 reared), but found 15 on a the apices of the paraprocts. The color pattern single palp in two specimens, and 16 and 17 on a was considered distinct or indistinct. Due to non- single palp in one specimen each. In P. hymenaea, uniform telescoping reported in the abdomens of he also found 16 or more palpal setae on at least larval and exuvial specimens (see Calvert 1934; one palp in each of 13 specimens examined (1 Huggins & Harp 1985), the posteriormost dis- reared), but found 15 on a single palp in one spec- tance on segment IX attained by the lateral imen. spines of VIII was not evaluated. Also, precise Needham & Westfall (1955) presented two measurements of the relative lengths of the move- novel characters to distinguish between species of able hook and crenulations of the labial palps Pantala. They characterized the epiproct of P. fla- were very difficult to obtain without damaging vescens as longer than the paraprocts, and that of the specimens, and were evaluated comparatively P. hymenaea as subequal to the paraprocts. This between species. The convexity of the dorsal mar- distinction was adopted by Young & Bayer (1979). gin of the epiproct in lateral view also was evalu- Paulson (1966) believed this to be a fairly reliable ated comparatively. distinction, but found some specimens of each Material examined.—CALIFORNIA: Fresno species to be indistinguishable based on this dis- Co., Enterprise Canal E. Clovis, 1 Nov 1976, S. W. tinction. Musser (1962) also agreed that this was Dunkle (exuviae of 4 reared P. hymenaea); FLOR- generally the case, but found measurement of IDA: Alachua Co., NE Gainesville, Nov 1975, S. W. these characters too difficult to reliably quantify Dunkle (exuviae of 6 reared P. flavescens); same and be useful. Needham & Westfall (1955) also data, Austin Cary Fishpond, coll. 22 Sep 1978, distinguished P. hymenaea from P. flavescens on emerged 23 Sep 1978, S. W. Dunkle (exuviae of 1 the basis of a more marked color pattern in the reared P. flavescens); MISSOURI: Audrain Co., R. former, which also was adopted by Young & Bayer M. White II Conservation Area, Sep 9, 1998, (1979). Paulson (1966) and Musser (1962) both re- BHPL & N. Whiteman (2 P. flavescens larvae); futed this distinction as unreliable, yet it ap- Benton Co., Lost Valley Fish Hatchery, 6 Oct peared again in Needham et al. (2000). 2000, L. Trial (exuviae of 3 unreared, 1 larval P. flavescens); Boone Co., Ditch near Vet. School, MATERIALS AND METHODS University of Missouri campus, 30 Jul 2001, BHPL (exuviae of 1 reared, 3 larval P. hymenaea); A total of 46 specimens of Pantala was exam- Christian Co., SW Nixa, ca. 200 gallon stock tank, ined. Of these, 27 specimens were P. hymenaea: 15 Aug 2001, BHPL (exuviae of 11 reared P. hyme- 23 from Missouri (16 reared exuvial specimens, 7 naea); Jackson Co., Jacomo Lake, no date, S. final instars) and 4 from California (all reared ex- Thewke (1 P. flavescens larva); Pemiscot Co., Uni- uvial specimens). Nineteen specimens of P. flave- versity of Missouri Lee Farm, rice paddy, 25 Jul scens were examined, including 12 from Missouri 2001, BHPL & C. Luppens, (exuviae of 1 reared, (1 reared exuvial specimen, 11 final instars) and 7 1larval P. flavescens; exuviae of 3 reared, 4 larval from Florida (all reared exuvial specimens). Mis- P. hymenaea); Texas Co., 4 mi. S Simmons, 4 Oct souri specimens are deposited in the Enns Ento- 1972, S. Thewke (3 P.