Pseudagrion pruinosum ( Burmeister, 1839 )

Saetung, Tosaphol & Boonsoong, Boonsatien, 2016, Description of the final instar larva of Pseudagrion pruinosum (Burmeister, 1839) (Odonata: Coenagrionidae) from Thailand, Zootaxa 4175 (3), pp. 292-300 : 293-295

Final instar of Pseudagrion pruinosum ( Burmeister, 1839)

Material examined. 10 adults and their exuviae (5 Ƌ 5 ♀), THAILAND; 1Ƌ 2♀, 14.III.2015, Kang Som Meaw (13°24′28″N, 99°16′52″E, altitude 200 m), Ratchaburi province, T. Saetung leg.; 1Ƌ, 15.III.2015, Swiss Valley Resort (13°30′33″N, 99°17′11.8″E, altitude 17.53 m) Ratchaburi province, T. Saetung leg.; 1Ƌ 1♀, 11.IV.2015, Huay Khayeng (14o36′20′′N, 98o34′38′′E, altitude 206 m) Kanchanaburi province, T. Saetung leg.; 1Ƌ 1♀, 22.III.2015, Sarika Waterfall (14o17′46′′N, 101o16′11′′E, altitude 26.2 m) Nakhon Nayok province, Thailand, T. Saetung leg.; 1Ƌ 1♀, 22.III.2015, Nang Rong Waterfall (14o18′50′′N, 101o18′24′′E, altitude 37.2 m) Nakhon Nayok province, Thailand, T. Saetung leg.

Description. Overall, the larvae were small ( Fig. 1 ), with very slender bodies, and a coloration that varied from yellowish brown to bright green ( Figs. 2–3 ).

Head: 2.5x wider than long, with a smooth, concave occiput, round postocular lobes with minute spines, and a concave posterior margin, with three prominent ocelli. Compound eyes narrow and rounded, protruding laterally. Antennae 1.23x longer than maximum head width, filiform, and 7–segmented, antennomere III longest, I and II similar in length; relative length of antennomeres 1.00 (0.54 mm): 1.00: 1.10: 0.85: 0.45: 0.25: 0.20 ( Fig. 4 ). Labrum setose, clypeus smooth. Mandibles ( Figs. 5–8 ) with molar teeth, but lacking a molar crest, with the following formula: L 1+1’234y a / R 1+1’234 y a. Prementum ( Fig. 9 ) subpentagonal, articulation of prementum and postmentum at level of posterior margin of coxae, with one premental seta and a row of three minute setae on each side of midline. In addition, a row of 6–10 spiniform setae along distal half of lateral margins, and a prominent spoon-shaped ligula with minute setae along the margin. Labial palp ( Fig. 10 ) as long as 0.67x prementum length, with premental setae 3 on each side; apical lobe ending in well-developed end hook, a truncate, denticulate lobe with 5 teeth on anterior margin, and a movable, slender, and curved hook 0.64x as long as palp length. Maxilla: Galeolacinia ( Fig. 11 ) with 6 teeth, apical tooth the largest, three dorsal teeth of approximately same size, and three ventral teeth of different sizes.

Thorax: Narrower than head, middle lobe of prothorax with a shallow groove in middle. Pronotum approximately hexagonal, glabrous, lateral margins rounded, pronotal disc smooth. Synthorax mostly glabrous, wing pads mostly pale, anterior and posterior wing pads reaching distal margin of S4. Long, thin femora with irregular dark spots and scattered spines, with the hind femora as long as 2x length of fore and mid femora. Borders of tibiae with scattered tridentate setae and a few unidentate setae ( Fig. 12 ). Tarsal formula 3–3–3, with 2 simple claws and a pulvilliform empodium.

Abdomen: Slender and cylindrical, narrowed caudally, abdominal terga with dark spiniform setae, with a pale, longitudinal band along midline of each segment and a darker stripe to each side of this pale band. Posterior margins with a row of minute spiniform setae. Abdominal sterna with a distinct network of tracheoles, scattered spiniform setae, and a dark stripe along midline. Male gonapophyses ( Figs. 13–14 ) sharply pointed, widely divergent in ventral view, reaching basally 1/3 length of sternite 10, with a row of 8–10 spiniform setae on ventral margin and 3 spiniform setae on lateral one. Female gonapophyses ( Figs.15–16 ) with lateral valves slightly divergent and tips sharply pointed, lateral valves extending to mid-length of S10 sternite, and a row of claviform setae along ventral margin; central valves slender, apically rounded, and slightly shorter than lateral valves.

Caudal lamellae distinct, transparent, β–nodate vertical lamellar type, with division between the two portions of the gill being marked by a nodal line consisting of a thickened basal portion (antenodal region) and a thinner distal portion (postnodal region). Lamellae with well-developed tracheation, a median trachea with secondary and tertiary branches, a few dark spots on the last branches, and a postnodal region with piliform setae on the margin. Median gill ( Fig. 17 ) with a dorsal and a ventral nodal spine at end of antenodal region, with 27–31 spiniform setae on dorsal margin and 10–13 sparse spiniform setae on ventral margin; latero-median carinae with 18–22 spiniform setae on each side. Lateral gills ( Fig. 18 ) with dorsal and ventral nodal spine on antenodal region, 22–30 spiniform setae on ventral margin, 10 spiniform setae on dorsal margin, and 23–29 spiniform setae on outer side of median carina.

Measurements (in mm), with mean plus range in parentheses, as follows (n=10): total length 22.05 (21.2– 23.3), length of caudal lamellae 5.11 (4.5–5.8), maximum width of head 1.56 (1.2–1.97), length of antennae 2.33 (2.16–2.45), maximum width of prementum 1.90 (1.8–2), length of prementum 2.60 (2.4–2.83), length of labial palp 1.08 (0.93–1.2), length of movable hook 0.70 (0.67–0.73), length of inner wing pads 5.24 (5–5.5), length of outer wing pads 4.76 (4.5–5), length of fore femora 1.5 (1–2), length of fore tibiae 1.92 (1.27–2.13),

length of fore tarsi 0.77 (0.5–1), length of middle femora 1.97 (1.33–2.67), length of middle tibiae 2.08 (1.5–2.5), length of middle tarsi 0.9 (0.43–1), length of hind femora 2.74 (2.4–3), length of hind tibiae 2.59 (2.07–2.97), and length of hind tarsi 1.06 (1–1.2).

Biological notes. Larvae of P. pruinosum were collected from the roots of vegetation in shallow pool/riffle habitats on the banks of streams. The larvae were usually found together with those of Copera marginipes , Euphaea masoni, Libellago lineata, Neurobasis chinensis , Pseudagrion rubriceps , and Prodasineura autumnalis .

Figures

FIGURE 1. Pseudagrion pruinosum: (1) final instar larva, dorsal view. Scale = 1 mm.

FIGURES 2 – 3. Pseudagrion pruinosum (Burmeister, 1839): coloration of last instar larvae, lateral view; (2) yellowish brown; (3) bright green.

FIGURES 4 – 12. Pseudagrion pruinosum: (4) antenna; (5) right mandible, ventrointernal view; (6) right mandible, internal view; (7) left mandible, ventrointernal view; (8) left mandible, internal view; (9) prementum, dorsal view; (10) left labial palp; (11) right maxila, ventral view; (12) tibial comb. Scale = 0.1 mm.

FIGURES 13 – 18. Pseudagrion pruinosum: (13) male gonapophyses, ventral view; (14) male gonapophyses, lateral view; (15) female gonapophyses, ventral view; (16) female gonapophyses, lateral view; (17) median gill; (18) lateral gill. Scale = 0.1 mm (13, 15); 0.2 mm (12, 14); 1 mm (16, 17).