Nephrotoma flavescens Linnaeus, 1758

Podeniene, Virginija, Naseviciene, Nijole & Podenas, Sigitas, 2014, Notes on the first instar larvae of Ctenophora and Nephrotoma (Diptera, Tipulidae), Zootaxa 3764 (2), pp. 152-168 : 157-159

Nephrotoma flavescens Linnaeus, 1758

( Figs. 18–32 )

First instar larvae. Length 1.75–1.78 mm; width 0.29–0.30 mm. Body covered with pale pubescence. Cuticle is transparent.

Head capsule. Length 0.36–0.38 mm; width 0.16–0.18 mm. Head capsule is prognatous and hemicephalic. It is elongate-oval in shape, slightly depressed dorsoventrally and, differently from the head capsule of the last instar larvae, just slightly sclerotised ( Fig. 18 ). Internolateralia and externolateralia are separated by incisions, which reach almost half-length of head capsule; each incision is continuous with deep groove (the most sclerotised part of head capsule) that extends almost to the base of antenna. Externolateralia are widely separated on the ventral side of capsule ( Fig. 19 ). Premaxillary suture separates side plates from the rest of head capsule. Side plate is wedgeshaped with a long anteromedial seta. Hypostomium is strongly sclerotised. It bears five sharp teeth. The outhermost teeth (both on dorsal and ventral part) are much smaller than the other. Small incision is on posterior part of hypostomium ( Fig. 20 ). Basally the hypostomium is fused with ventral margins of genae and with side plates. Prementum is visible from below. It is very similar to that of Ct. guttata . Frontoclypeus is short (4/5 times as long as internolateralia) and fused with internolateralia. Internolateralia are separated by fold on posterior part ( Figs. 18, 19 ). Internolateralia are much longer than externolateralia. Clypeal part of frontoclypeus is membranous and separated from labrum by deep fold. There are four short setae on the anterior part of clypeus. A short seta is situated below the anterior part of clypeus towards the base of antenna. There are four short setae below the base of antenna ( Fig. 18 ). Ecdysial and coronal sutures are not visible. Labrum is rectangular in shape and composed of two wedge-shaped sclerotised plates separated by membranous areas. Each labral lobe has distinct triangularly shaped outgrowth directed outward ( Fig. 21 ). Apical part of labrum and ephipharynx are covered with numerous hairs. One long and one short seta present on membranous part on each side of labrum ( Fig. 22 ). One long, one medium-length, two short setae and one sensory pit present on anteriolateral part, two sensory pits present on medial part, one short and one very short setae are located on posterior part of labral lobe. Antenna is short and composed of one cone-shaped segment, almost as long as wide at base ( Fig. 23 ). It has a large cone-shaped and a few small peg-like apical sensillae and subapical posterodorsal sensory pit. Mandible is one-segmented and much more sclerotised than the rest of head capsule. Five sharp teeth are present on both mandibles ( Fig. 24 ). Apical, first ventral and dorsal teeth are the most prominent. Second dorsal and second ventral teeth are much smaller. Prostheca or lacinia mobilis present on the dorsal side of inner surface of mandible ( Fig. 24 ). Lacinia mobilis is arch-shaped, with 9–10 sharp small teeth on apical part and with cushion of long hairs in the middle. Lateral surface of mandible has two very short setae at the base. A sensory pit is present at the base of dorsal side. Mandibles operate in horizontal plane. Inconspicuous larval eye spot is present below the base of mandible. Maxilla has triangularly shaped cardo, which bears two almost equal setae near the distal end ( Fig. 25 ). There are two sclerites on stipes. The inner sclerite extends around inner margin of maxilla onto its dorsal surface and the outer sclerite extends around outer margin of maxilla to its dorsal surface ( Fig. 25 ). Galea and lacinia are fused. Galea is covered with numerous short hairs. There are three long sensory structures on the ventral side of galea. Lacinia has three sharp pointed outgrooves on the outer margin.

Thorax. All thoracic segments are short and wide, covered with microscopic hairs. Prothorax has dorsal and ventral pads ( Figs. 26, 27 ).

Abdomen. Abdominal segments are longer than wide. They are covered with two types of hairs. Short hairs cover lateral parts of segment and big portion of tergal and sternal parts. Tips of these hairs are three-branched ( Figs. 28 ). Long hairs form lines on tergal and sternal parts of segments. Setae are light brown. Setae D1 and D6 are very short; D4 and D5 are twice as long as D1; D2 is three times as long as D1; D3 is more than five times as long as D1. Setae D2, D3 and D4, D5 make pairs and are very close to each other ( Fig. 29 ). Setae V1 and V2 are equal in length and twice as long as V3 and V4. Setae V1, V2 and V3, V4 make pairs and are close to each other ( Fig. 30 ). Setae L1, L2 and L3 are close to each other ( Fig. 31 ). L2 is short; L1 is three times as long as L2 and twice as long as L3; L4 is rather far away from other setae and its length is similar to that of L3.

Hairs on sixth and seventh abdominal segments are longer than those on other segments. Third thoracic and first abdominal segments are wider than long. First and second thoracic and second to eighth abdominal segments are longer than wide. Last or anal abdominal segment is constricted.

Spiracular disc. Spiracular field is surrounded by four flat and elongate round-tipped lobes ( Fig. 32 ). Lateral lobe is prominent, its length almost 1.5x the width at the base. It has two long stout apical bristles. Each bristle is almost six times as long as the lobe itself and about as long as one-third of the whole body. Three tufts of two short bristles each present on dorsal part. There are three tufts of long bristles above the spiracles. The innermost and outermost tufts consist of two bristles, the middle tuft consists of three bristles. Ventral lobes are almost as long as wide at the base. A tuft of four long bristles is on the apical part of lobe and a tuft of three slightly shorter bristles is on inner part; two tufts of two short bristles each present on the outer margin; a tuft of four bristles different in length and a single bristle are at the base of lobe. Both pairs of lobes are almost completely covered with large, wedge-shaped sclerites. Spiracles are large, oval and close to each other. Distance between them is almost the same as diameter of a spiracle itself.

Anal field. Anus is surrounded by four short, white and fleshy anal papillae. There are few long setae on anal segment (here and in other Nephrotoma species below it was difficult to establish number and arrangement of setae due to preservation).

Specimens examined. 26 egg-larvae from 1 female, female was captured in Lazdijai district, N54.24080, E23.51548, 23 VI 2011, eggs were laid on 24 VI 2011, egg-larvae hatched on 17 VII 2011.

Figures

FIGURES 18 – 27. Nephrotoma flavescens, first instar larva: 18. General view head capsule, dorsal aspect. 19. General view head capsule, ventral aspect. 20. Hypostomium. 21. Lateral plates of labrum. 22. General view of labrum. 23. Right antenna. 24. Mandible. 25. Right maxilla, ventral view. 26. The first thoracical segment, dorsal view. 27. The first thoracical segment, lateral view.

FIGURES 28 – 32. Nephrotoma flavescens, first instar larva: 28. Abdominal segment, dorsal view. 29. Dorsal abdominal setae (segments II – VII). 30. Ventral abdominal setae (segments II – VII). 31. Lateral abdominal setae (segments II – VII). 32. Spiracular field.