Potamyia flavata, Banks 1934

Maneechan, Witwisitpong, Kruttha, Phassawat & Prommi, Taeng On, 2018, The larva and pupa of Potamyia flavata (Banks 1934) (Trichoptera: Hydropsychidae): Description, life cycle, and notes on its biology, Zootaxa 4394 (3), pp. 395-406 : 397-404

Description of the fifth-instar larva of Po. flavata Banks 1934

Larva: Total length 9.5–10.5 mm (n = 10). C-shape body typical for Hydropsychidae . Background color of head and notal sclerites yellow.

Head: Head capsule width 0.80–1.15 mm (n = 10). Entire head light yellow ( Figs. 2–4 ). Frontoclypeus with anterior margin concave, slightly crenulate; faint large spot anteromedially; pair of faint light marks immediately anterior of tentorial pits and faint light mark between them; posteromedian portion with one pair of small, pale, muscle scars and small cluster of muscle scars near posterior apex ( Fig. 5 ). Region around eyes and posterior quarter of head lighter yellow in dorsal view ( Fig. 3 ), ventral side darker along midline ( Fig. 4 ). Head covered with long setae, mingled with tapered setae on dorsal and lateral regions in anterior three-quarters ( Fig. 3 ). Labrum light-brown; elliptical in dorsal view; bearing dense and well-developed, brown setae anterolaterally and setae on dorsal surface, posterior margin slightly concave in middle ( Fig. 6 ). Mandibles with prominent lateral flanges, each with row of setae along lateral groove. Each mandible with 2 apical and 4 mesal teeth, right mandible with basal tooth distant from others, left mandible with mesal tuft of hairs ( Fig. 7 ). Submentum trapezoidal with posterolateral and anterolateral corners broadly rounded; anterior margin broadly Y-shaped with median cleft; cleft with sides parallel; lateral areas with setae ( Fig. 8 ). Anterior ventral apotome without or with weakly prominent anteromedian tubercle, lateral arms long, narrow, apically blunt, and posterior point acute; posterior ventral apotome small ( Figs. 4, 8 ).

Thorax: Nota yellow with covering of brown setae. Pronotum covered with long, truncate peg setae, mingled with tapered setae, same setae projecting beyond anterior margin ( Figs. 9–10 ). Meso- and metanota each covered with numerous, inclined, long, scale hairs; same setae projecting beyond anterior margin ( Figs. 9, 11–12 ). Prosternite broadly transverse, with broad dark band along posterior margin and with pair of small sclerites near posterolateral angles ( Fig. 16 ). Propleura ventrally with stout setae; foretrochantins unforked and each with rudimentary basodorsal ramus ( Fig. 13 ). Forelegs with feather-like setae mingled with palmate setae on mesal and lateral surfaces of coxae; trochanters and femora with long, feather-like setae on ventral surfaces mingled with long setae ( Fig. 13 ). Mid- and hind legs similar in size, shape, and structure; each with feather-like setae mingled with spike-like setae on posterior surface of trochanter, femur, and tibia ( Figs. 14–15 ). Mesosternum with one pair of gills; metasternum with 2 pairs of gills; gills consisting of central stem bearing many lateral filaments ( Fig. 2 ).

Abdomen: Abdominal segments with long, recumbent setae, more dense ventrally. ( Figs. 2 , 9 , 17–18 ). First sternum with 2 pairs of gills with adjacent bases ( Figs. 2 , 9 ). Segments II–V each with one pair of median gills. Segments II–VII each with one pair of lateral gills each arising from common base. Sterna VIII and IX each with pair of spike-bearing plates, sternum IX with spikes emanating from prominent sockets. Each sclerite of sternum IX entire posteriorly and triangular. Tergum IX with small lateral sclerite and pair of large ventral sclerites ( Fig. 17 ). Anal prolegs with bent apicoventral claw and apicodorsal cluster of long bristles, dorsal surfaces with spikelike setae, ventral surfaces without spike-like setae ( Figs. 2 , 18 ).

Pupa ( Figs. 19–22 ): Mandibles tapering regularly to pointed apex; inner margin with 4 large teeth ( Fig. 20 ); widened basally, with elongate setae on lateral and ventral surfaces. Dorsally, with 1 pair of anterior hook plates on each of abdominal segments III–VIII; 1 pair of posterior hook plates on each of segments III–IV ( Figs.19, 21–22 ), posterior hook plates of segment IV covered with row of long setae ( Fig. 21 ). Apical processes each with wide base narrowing distally to subapicolateral shoulder; apex obliquely truncate; ventral surface and lateral margins bearing long setae ( Fig. 22 ).

Diagnosis of larva: Several features distinguish the larva of this species from that of Po. phaidra Malicky & Chantaramongkol 1997 ( Prommi et al. 2006b). Specifically, the anterior ventral apotome of P. phaidra has a prominent anteromedian tubercle and cleft apex, whereas P. flavata has a weakly prominent anteromedian tubercle and the apex is not cleft. Potamyia phaidra has the ventral sclerites of abdominal sternum IX smaller and more widely separate, and with the inner margins concave, whereas for P. flavata , the ventral sclerites are each much broader than the space between them and the inner margins are straight. The lateral margins of the mandibles are strongly flanged for their entire length in Po. flavata , whereas for Po. phaidra , the flanges are not well-developed. Other noteworthy features that might be useful for distinguishing among the larvae of species of Potamyia include the size and shape of the black maculation on the midline of the posterior margin of the metanotum, color pattern on the head, and overall size.

Material examined: THAILAND: Ratchaburi Province: Phachi Nueng stream from Phachi watershed, 140 m, 13°32.135'N, 099°17.842'E, 26-ii-2015, Prommi, 180 larvae, 26 pupae, 15 male pupae, 56 male adults; Phachi Sarm stream from Phachi watershed, 171 m, 1327.658´N, 09915.348´E, 5-v-2015, Prommi , 133 larvae, 23 pupae, 15 male pupae, 98 male adults; Phachi See stream from Phachi watershed, 170 m, 13°34.078'N, 099°15.495'E, 4- xii-2015, Prommi, 127 larvae, 5 male adults; Phachi Harh stream from Phachi watershed, 219 m, 1322.563´N, 09916.585´E, 5-xii-2013, Prommi, 440 larvae, 126 pupae, 29 male pupae, 125 male adults; Phachi Hok stream from Phachi watershed, 180 m, 1348.379´N, 09919.152´E, 26-ii-2015, Prommi, 450 larvae, 59 pupae, 25 male pupae, 125 male adults; Phachi Jed stream from Phachi watershed, 175 m, 1331.017´N, 09927.449´E, 26-ii-2015, Prommi, 398 larvae, 98 pupae, 21 male pupae, 125 male adults; Phachi Phad stream from Phachi watershed, 123 m, 1334.275´N, 09921.778´E, 5-v-2015, Prommi , 405 larvae, 50 pupae, 59 male pupae, 59 male adults.

Larval instars of Potamyia flavata

Larval, pupal, and adult specimens were collected on all occasions during February, May, and December 2015 and revealed a multivoltine life cycle. The larvae were classified into five instars using 2,133 specimens. Head widths of first instars ranged from 0.20 to 0.29 mm (n = 22). Head widths of second instars ranged from 0.30 to 0.39 mm (n = 143), of third instars from 0.40 to 0.59 mm (n = 491), of fourth instars from 0.60 to 0.79 mm (n = 1,404) and of fifth instars from 0.80 to 1.15 mm (n = 73) ( Fig. 23 ).

Temporal distribution of larval instars varied among sampling sites ( Fig. 24 ). First instar larvae were absent from sampling sites PC1, PC4, PC7, and PC8 at all sampling times, whereas the second to the fifth instar larvae were found. Also, second instar larvae were not collected from sampling sites PC4 and PC8. Most third instar larvae were found at sampling site PC3, fourth instar larvae were present at sampling site PC7, whereas most fifth instar larvae were collected at sampling site PC8. All instar larvae were found at sampling sites PC3 and PC6.

Larval gut contents in Potamyia flavata in seven sampling sites

Larval gut contents were assessed qualitatively. Contents were separated into diatoms, green algae, filamentous algae, arthropod fragments, and detritus. Gut content analysis indicated that larvae are omnivorous filterers. The predominant items were diatoms and green algae followed by filamentous algae, detritus, and arthropod fragments ( Fig. 25 ).

Biology and habitat

The specimens were found in small and medium streams in the Phachi watershed, western Thailand, at altitudes between 123 and 220 m asl. The streams have moderately clean and slightly warm water. The annual temperature range at this site is between 26.30–29.83°C (Prommi, in press). The majority of larvae and pupae were collected in stream sections where the flows run past villages and agricultural areas. The larvae were found on substrate consisting of cobbles, pebbles, and gravel with relatively moderate–fast running waters. They construct a typical hydropsychid fixed tubular retreat with a silken filter net at the entrance, in which larvae capture small food items. The pupae were found abundantly in more slowly flowing water, with shelters firmly attached to rocks. Based on collecting data of the studied material, Po. flavata has multiple generations per year.

Other Potamyia caddisflies inhabiting the same stream habitats are Po. phaidra .

Discussion

A total of thirteen Potamyia species are recorded from Thailand. Potamyia phaidra and Po. flavata have the most widespread distributions ( Thapanya et al. 2004). Larvae of Po. phaidra and Po. flavata were associated with corresponding adults using metamorphotypes and have now been described ( Prommi 2006b; Prommi, in press), those of the other 11 Thai species have not been described. The other 11 species have broad areas of Thailand in which they have not been collected. Naturally, the known distribution of a species does not necessarily represent its actual distribution, in part because of regionally sporadic sampling efforts. For example, Po. flavata was not found in southern Thailand, but is widespread and common in northern and western Thailand and further south in Sumatra, Java, and Bali. Other congeners might be endemic to particular areas further north and west ( Malicky & Chantaramongkol 1999). Although adults of Potamyia species are known from China, the larval stages have not been recorded ( Dudgeon 1999) except for Po. chinensis ( Ulmer 1915; Zhou 2007) after the larva and male of that species were associated using DNA sequences.

Southeast Asia harbors the highest diversity of Trichoptera on the planet ( Schmid 1984; Morse 2016). However, most taxonomic studies have focused on adults. As a consequence, very few taxonomic studies have addressed the immature stages which, ironically, are more important from a water quality perspective. Clearly, more descriptions of larval morphology and biology are needed to enable a refined understanding of the benthic fauna in southeast Asian streams.

Figures

FIGURE 23. The frequency distribution of larval instars of Potamyia flavata Banks 1934 at all sampling sites, based on head capsule width (n = 2,133).

FIGURE 24. Phenological distribution of larval instars of Potamyia flavata Banks 1934 at all sampling sites.

FIGURE 25. Gut contents from Potamyia flavata Banks 1934 larvae. A = diatoms, B = green algae, C = detritus, D = filamentousalgae, E = insect legs.

FIGURES 2–8. Larva of Potamyia flavata Banks 1934: 2, habitus, right lateral; 3, head, dorsal; 4, head, ventral; 5, frontoclypeal apotome, dorsal; 6, labrum, dorsal; 7, mandibles, ventral; 8, submentum and anterior ventral apotome, ventral.

FIGURES 9–15. Larva of Potamyia flavata Banks 1934: 9, head and thorax, right lateral; 10, pronotum, dorsal; 11, mesonotum, dorsal; 12, metanotum, dorsal; 13, foretrochantin and outer face of right foreleg, posterior; 14, inner face of left midleg, anterior; 15, inner face of left hind leg, anterior.

FIGURES16–18.Larva of Potamyia flavataBanks 1934:16, prosternum,ventral;17, sterna VIII and IX, ventral; 18,terminal abdominal segments and anal prolegs, right lateral.

FIGURE19–22. Pupa of Potamyia flavata Banks 1934: 19, habitus, left lateral; 20, left mandible, ventral; 21, abdominal terga III–V, dorsal;22, apical processes of abdomen, dorsal.