Male. Head brown, antennae slightly brown (Fig. 2); pronotum paler than head, anterior margin wider than posterior margin. A single unbranched cervical gill as typical of the genus present on each side of mid-line (Fig. 1A). Wings subhyaline, fumose, veins brown. Forewing length ca. 6 mm, hind wing 5.5 mm. Legs brown (Fig. 2). Tergum 9 slightly sclerotised, extending posteriorly as a broad lobe over tergum 10. Tergum 10 slightly sclerotised anteriorly, but being more sclerotised along the posterior margin where a pair of lateral knobs and a pair of strong median prongs are present, both most noticeable in dorsal view, a field of 5-6 tiny spines present anteromedially (Fig. 1B). Hypoproct broad basally and tapering to a small, narrow tip, vesicle plump, length 2x width (Fig. 3B). Cerci mostly membranous, long thin and bent inwards (Fig. 1B, Fig. 3A-C). Paraprocts divided into two lobes; inner lobe slightly sclerotised, thin and long; outer lobe broad basally, large triangular, outer part curving dorsally, with outer margin darkly sclerotised and with outward directed sclerotised prong from outer margin near cerci (Fig. 3B and D). Epiproct short and broad in dorsal aspect; dorsal face with a pair of sclerotised bands each side of mid-line and distal margin of dorsal sclerite darkly sclerotised, extending anterolaterally, enveloping tip of ventral sclerite, which is more distinct in lateral and ventral views; basal sclerite membranous; ventral sclerite strongly sclerotised, broad basally and with lateral knobs at basolateral corners, becoming narrower towards apex, forming a pair of ridges each side of mid-line, each bearing a row of spines on anterior half (Fig. 3E-G).

The male of this species is characterised by two pairs of small knobs arising posteromedially from tergum 10. They are similar to I. tuberostyla (Wu 1962) in the lateral view of the epiproct, both looking like tumours, but can be separated from the latter by the knobs protruding from the posterior margin of tergum 10. In I. tuberostyla, there was no mention of knobs on the terga.

The name refers to the pair of knobs and strong prongs located posteromedially on tergum 10. The Latin adjective “tuberculata” means having knobs.

China: Sichuan Province.

Male. Head and antennae slightly brown; pronotum brown, angles blunt rounded (Fig. 4). A single unbranched cervical gill on each side of mid-line (Fig. 5A). Wings hyaline, veins brownish. Forewing length 4.8 mm, hind wing 4.0 mm. Legs brown. Abdomen pale with hairs. Tergum 10 bearing several small spines on anterior part and forming a pair of pale knobs medially, with hairs on the rounded tip (Fig. 5B and Fig. 6C). Hypoproct sub-quadrant with a small narrow tip; vesicle short, length 2x width. Cerci membranous, very long and thin with many hairs, upcurved in lateral view, sinuous in dorsal view (Fig. 6A-C). Paraprocts divided into 2 lobes; inner lobe slightly sclerotised, thin and short; outer lobe membranous mostly, broad basally, tapering to the apex, outer margin slightly sclerotised (Fig. 5C and Fig. 6A). Epiproct heart-shaped; dorsal sclerite notched apically, median part forming a pair of sclerotised bands, with a thin and slightly sclerotised protrusion between the sclerotised bands, outer margins of sclerotised bands bearing spinules; ventral sclerite with a pair of slightly sclerotised bands, each band bearing many spines (Fig. 6D-E and Fig. 7A-C).

The male of this species is characterised by the heart-shaped epiproct with a thin and slightly sclerotised structure projecting between the sclerotised bands. In I. tuberostyla (Wu 1962) and I. bituberculata sp. nov., the epiprocts are tumour-shaped and there are no structures projecting from the epiproct.

This species is named after the type locality, Medog County. “Motuo” is the spelling of “Medog” in Chinese pinyin.

China: Tibet.

Male. Head brown, antennae slightly brown (Fig. 9); pronotum brown with dark brown stripes, anterior margin wider than posterior margin. A single unbranched cervical gill on each side of mid-line (Fig. 8A). Wings subhyaline, with light spots, veins brown. Forewing length 5.9 mm, hind wing length 5.0 mm. Legs brown, the middle of femora slightly brown. Anterolateral margin of terga 1–5 sclerotised. Terga 6-9 sclerotised anteriorly, but concave mid-anteriorly. Tergum 10 sclerotised, with a pair of small knobs near mid-length at each side of mid-line, which is more distinct in lateral view, with a small oval membranous portion above the knobs. Hypoproct broad basally and tapering to the tip; vesicle plump, rectangular, length 2x width. Cerci light brown, bent inwards and upwards, with hairs (Fig. 8B-C, Fig. 10A and Fig. 11A-C). Paraprocts divided into 2 lobes; inner lobe slightly sclerotised, short, sub-oval; outer lobe sclerotised, except inner margin, outer margin darkly sclerotised, broad basally, then slender, with a pointed tip (Fig. 11B and E). Epiproct short and broad, stretching back in side view, with the tip curved down; dorsal sclerite with a pair of sclerotised curved bands each side of mid-line, extending forward. Median part of epiproct with a pair of transverse sclerotised stripes, bearing spinules laterally; ventral sclerite slightly sclerotised, forming a pair of ridges each side of mid-line, each bearing a row of spines (Fig. 10B and Fig. 11D).

The male of this species is characterised by a pair of small knobs from tergum 10, outer lobe of paraprocts with a pointed tip and epiproct bearing spinules laterally. It is similar to I. tuberostyla (Wu 1962) and I. bituberculata sp. nov. in the tumour-shaped epiproct. However, in I. tuberostyla, there is no portion extending from the epiproct anteriorly. It is similar to I. bituberculata in dorsal sclerite with a pair of sclerotised bent bands each side of mid-line. However, the length of the portion extending anteriorly is twice as long than that in I. bituberculata. Median part of dorsal sclerite in I. weii bears a pair of transverse sclerotised stripes, forming spinules laterally, which are absent in I. bituberculata.

This new species is named in honour of Professor Wei Mei-Cai (Central South University of Forestry and Technology, Changsha, Hunan, China), a taxonomist of Chinese sawfly (Hymenoptera, Symphyta) for organising the biodiversity expeditions in Tibet, Qinghai and Sichuan.

China: Sichuan Province.