Myllocentrini, Massa, 2023

Massa, Bruno, 2023, Biodiversity hotspot in the Sangha Trinational Protected Area revealed through Orthoptera Tettigoniidae, Zootaxa 5331 (1), pp. 1-67 : 37-40

New Tribe Myllocentrini ( Figs. 23a– 23g , 24a–24d )

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According to Ragge(1962) the genus Myllocentrum Ragge,1962 is not related to the genera of the tribe Phlaurocentrini , though shares with them the greatly reduced ovipositor. Actually, the fastigium of the vertex of Myllocentrum is not as compressed as in Phlaurocentrum Karsch, 1889 , Buettneria Karsch, 1889 and Leiodontocercus Chopard, 1954 , the legs are clearly shorter, and the last tergite of both sexes is unmodified. For similar reasons Ragge (1962) excluded its affinity with Enochletica Karsch, 1896 and consequently Myllocentrum was not included in the tribe Preussini Karsch, 1890 . Considering the peculiarity of the two species belonging to the genus Myllocentrum [ M. stigmosum (Karsch, 1896) and M. raggei Massa, 2013 ] ( Figs. 23a, 23b ), a distinct tribe is proposed for this genus, Myllocentrini new tribe.

Diagnosis of the new Tribe Myllocentrini . Medium sized, fastigium of vertex narrow, a little raised, pointed and furrowed, as large as first antennal segment, face large and short ( Fig. 23c ). Eyes round, prominent, scapus placed within an area with raised margins. Pronotum flat and smooth, nearly as long as high, moderately compressed, with lateral margins and well-developed humeral excision, lateral lobes rounded on hind and lower margins. Legs short and slender; fore coxae armed, fore femora inferiorly sulcate. Tympana conchate on inner side, open on outer side. Dorsal margin of fore tibiae furrowed. Tegmina well developed, slightly shorter than hind wings. Mirror absent. Fairly exclusive is the presence of conspicuous, prominent and regularly placed small bristles on 6–7 veinlets in the anal area of the right female tegmen ( Figs. 23d, 23e ), certainly involved during the female reply to male song. Medial field with crossed veinlets, two apically divided branches radiate from radial vein. 10 th tergite unmodified, subgenital plate a little concave, provided with short styli. Cerci stout and incurved. Females with ovipositor much reduced, apically pointed ( Fig. 24a ). Black spots on the tegmina and black markings on the body characterize the two species of the genus Myllocentrum ( Figs. 23a, 23b ).

Remarks. Ragge (1962) already highlighted the presence of veinlets in the anal area on the right female tegmen certainly used to produce sounds.Analogous structures have been found in most females of Phaneropterinae ( Heller et al. 2015) and a similar acoustic system has been noticed on the female right tegmen of the genus Arantia (tribe Holochlorini ) ( Hemp & Massa 2017). In addition, females belonging to the tribe Phlaurocentrini have these structures, but unlike Myllocentrum , they are placed rather irregularly on the right tegmen, not on parallel veinlets ( Figs. 23f, 23g ).

There is also an important morphological difference in the ovipositor shape between the new tribe Myllocentrini and that of Phlaurocentrini ; species belonging to the new tribe Myllocentrini have an ovipositor of normal shape, but reduced in size. Both valves, ventral and dorsal are flattened laterally, directed upwards and are parallel ( Fig. 24a ), while in Phlaurocentrini the valves of the ovipositor are not flattened laterally, the 10 th abdominal tergite of the female is hood-like and conceals the supra-anal plate; the ovipositor is much reduced and with smooth and short valves. Ventral valves of Phlaurocentrini are short, directed upwards and apically pointed, dorsal valves longer than ventral ones, straight like two short fingers ( Figs. 24b, 24c, 24d ). This has also ecological implications; the species belonging to the new tribe Myllocentrini , like the other Phaneropterinae , lay flat eggs between the layers of the leaf epidermis, while those belonging to the tribe Phlaurocentrini lay round and thick eggs between cracks of tree bark (Massa 2020).

Figures

FIGURE 23. Habitus of Myllocentrum stigmosum (Karsch, 1896) (a) and M. raggei Massa, 2013 (b), frontal view of the head (c), dorsal view (d) and frontal view of female right tegmen of M. raggei (e) (new tribe Myllocentrini), frontal view of female right tegmen in Phlaurocentrum sp. (f) and Leiodontocercus sp. (g) (tribe Phlaurocentrini Karsch, 1889). Arrows show the peculiar area of veinlets certainly involved in the female song.

FIGURE 24. Lateral view of the ovipositor of Myllocentrum raggei Massa, 2013 (a), Leiodontocercus spinicercatus Massa, 2020 (b), Buettneria maculiceps Karsch, 1889 (c) and Phlaurocentrum latevittatum Karsch, 1889 (d) to show differences between the new tribe Myllocentrini and the tribe Phlaurocentrini Karsch, 1889.