Simulium (Inseliellum) raivavaense Craig and Porch

Craig, Douglas A. & Porch, Nick, 2013, Subfossils of extinct and extant species of Simuliidae (Diptera) from Austral and Cook Islands (Polynesia): anthropogenic extirpation of an aquatic insect?, Zootaxa 3641 (4), pp. 448-462 : 456-457

Simulium (Inseliellum) raivavaense Craig and Porch , sp. nov.

Figures: 14–17

Diagnosis. Larva: hypostoma with three sublateral teeth, lateral tooth and two paralateral teeth broadly flattened and slightly recurved medially. Frontoclypeal apotome with pigmentation not in figure eight configuration. Postgenal cleft U-shaped.

Description (Based on holotype, paratypes and numerous other specimens).

Adults. Unknown.

Pupa. Unknown.

Larva. Last instar. Head capsule: moderately pigmented, the postocciput and hypostoma more so ( Fig. 15 ). Frontoclypeal apotome ( Fig. 14 ): cuticle corrugated with bases of sensilla raised, neither markedly so; with darker medial and posterior pigmentation, similar to that of S. teruamanga ( Fig. 2, 7 ), markedly different from that of S. rurutuense ( Fig. 9 ); ecdysial line not sinuous, sharply rounded posterolaterally ( Fig. 14 ). Hypostoma ( Fig. 16 ): median tooth distinct, apex markedly posterior to line of lateral teeth; three sublateral teeth small and flanged; lateral tooth and two paralateral teeth markedly prominent, flattened and slightly recurved medially; serrations three to five, small, sharp. Five hypostomal sensilla. Postgenal cleft U-shaped, smoothly rounded apically ( Fig. 14 ). Posterior tentorial pits not markedly developed, albeit distinct. Mandibular phragma not markedly extended ventrally.

Probable penultimate instar. Hypostoma ( Fig. 17 ). Median tooth prominent, sublateral teeth of equal length, lateral tooth and paralateral teeth as for last instar; serrations three, as for last instar. Three hypostomal sensilla.

Type data. Holotype: Microscope slide, ventral head capsule of larva. Label details:- " Simulium / (Inseliellum)/ raivavaense / Austral Islands/ Raivavae, nr. Rairua/ S23.86851 W147.67853 / Acq. #17239 BPBM/ PVLP D. A. Craig. 2010/ HOLOTYPE (red)". Deposited Bernice P. Bishop Museum, Honolulu, Hawai'i.

Paratypes—four. As for holotype, but with PARATYPE. One probable penultimate instar with frontoclypeal apotome deposited Bernice P. Bishop Museum, Honolulu. Three, one of penultimate instar, deposited Australian National Insect Collection (ANIC), CSIRO, Canberra, Australia.

Material examined. Holotype, paratypes, numerous other specimens.

Distribution ( Fig. 1 ). Austral Islands, Raivavae.

Etymology. Named for the Austral Island, Raivavae.

Remarks. Recognizing a species of simuliid merely on the basis of incomplete subfossil larval head capsules is problematic. However, the hypostomata are well preserved, including one frontoclypeal apotome, and provide clear evidence about the specific distinctiveness of this material. Using the hypostoma as a major diagnostic character for species has been successfully employed by Craig and Joy (2000) for Polynesian simuliids and the overall problem was discussed by Craig (1987, 1997). Simulium raivavaense differs markedly in hypostomal expression from that of extant S. rurutuense from Rurutu ( Fig. 3, 4 ) and subfossil material from Tubuai. The median and sublateral teeth are relatively similar in size, but the lateral and paralateral teeth differ— S. rurutuense has five to six paralateral teeth, whereas there are only two markedly enlarged such teeth in S. raivavaense . In S. rurutuense the median tooth is subequal in length to the most prominent lateral teeth ( Fig. 11 ), whereas in S. raivavaense the median tooth is markedly shorter ( Fig. 16 ). The serrations also differ distinctly—small and rounded in S. rurutuense , sharp and distinct in S. raivavaense .

There is little question that S. raivavaense falls within the Cook-Austral Islands clade of species ( S. teruamanga plus S. rurutuense ), agreeing in expression of hypostomal teeth, cuticular corrugation and raised sensilla bases. That this is probably the correct grouping is confirmed by the poorly developed ventral extension of the mandibular phragma in S. raivavaense . This character state is expressed in the majority of Inseliellum species, but not a small segregate of Society Islands species, the mesodontium -subgroup, which have superficially similar hypostoma.

Simulium raivavaense and S. rurutuense can be distinguished from S. teruamanga by possession of only three sublateral teeth on either side of the median tooth of the hypostoma; the latter species has four.

Subfossil simuliid material from Raivavae included a single specimen that retained the frontoclypeal apotome and shows specific differences from S. rurutuense . The apotome has a pigmentation pattern ( Fig. 14 ), albeit faint, more like that of S. teruamanga ( Fig. 2 ), not the figure-of-eight shape diagnostic for S. rurutuense ( Fig. 9 ). Further the hypostomal teeth have only two paralateral teeth and the serrations are developed as small teeth, not rounded structures as for S. rurutuense . The median tooth is poorly developed (cf. Fig. 11, 16 ). That this is a derived condition is bolstered by the more generalized development of the teeth in a penultimate instar subfossil ( Fig. 17 ) where the median tooth is more prominent. Such ontogenetic development of apomorphic hypostomal teeth is well known for Inseliellum (Craig 1997).

The site of collection of this material is today an extensively weed-invaded former taro swamp: immediately adjacent to the core site there are extensive contemporary taro gardens. Prior to human arrival (sometime not long before 1300AD) the sediments suggest significantly more running water and a forested landscape paralleling the general trends in other palaeo-records from the region (Anderson and Kennett 2012).

Rapa-iti, often referred to as Rapa, further to the east lacks introduced fish and crustaceans (Englund 2004). Simuliids are not known from this island, neither are subfossils, so an assumption might be that they never reached this far east. Rapa appears to have less biogeographic affinity to the other Austral Islands than it does to the Society Islands (Englund 2004; Gillespie et al. 2008). A sedimentary sequence from Rapa (Core 2 of Prebble et al. 2012) has been examined for insect remains and despite containing extensive subfossil insect material, none are of simuliids.

Figures

FIGURE 1. Distribution of known simuliid material on Cook and Austral Islands. Simulium (I.) teruamanga — squares, S. (I.) rurutuense — circles. Simulium (I.) raivavaense — asterisk. Solid shapes indicates extant species, stippled subfossil material. (Adapted from Craig et al. 2001).

FIGURES 9 – 17. 9 – 13. Simulium (I.) rurutuense. Fig. 9. Dorsal view of head of extant larva. Vaipapa Stream, Rurutu (scale bar 0.1 mm). Fig. 10. Hypostoma and postgenal cleft of extant larva (scale bar 0.1 mm). Fig. 11. Hypostoma of extant larva (scale bar 0.02 mm). Fig. 12. Hypostoma, postgenal cleft and genae of subfossil larva. Mihiura Swamp, Tubuai (scale bar 0.1 mm). Fig. 13. Hypostoma of subfossil larva (scale bar 0.05 mm). 14 – 17. Simulium (I.) raivavaense. Near Rairua, Raivavae. Fig. 14. Frontoclypeal apotome of extinct subfossil larva—note anteromedial palatal brush (scale bar 0.05 mm). Fig. 15. Hypostoma, postgenal cleft and genae of extinct subfossil larva (scale bar 0.05 mm). Fig. 16. Hypostoma of last instar of extinct subfossil larva (scale bar 0.02 mm). Fig. 17. Hypostoma of probable penultimate instar of larva (scale bar 0.02 mm).

FIGURES 2 – 8. Simulium (I.) teruamanga. Fig. 2. Dorsal view of head of extant larva. Matavera Stream, Rarotonga (scale bar 0.1 mm). Fig. 3. Hypostoma and postgenal cleft of extant larva (scale bar 0.05 mm). Fig. 4. Hypostoma of extant larva (scale bar 0.02 mm). Fig. 5. Hypostoma, postgenal cleft and genae of subfossil larva. Near outlet Tamarua East swamp, Mangaia (scale bar 0.1 mm). Fig. 6. Hypostoma of subfossil larva. Near outlet Tamarua East swamp, Mangaia (scale bar 0.02 mm). Fig. 7. Hypostoma, postgenal cleft, frontoclypeal apotome and antenna of subfossil larva. Near Lake Te Roto, Atiu (scale bar 0.1 mm). Fig. 8. Hypostoma of subfossil larva. Near Lake Te Roto, Atiu (scale bar 0.02 mm).