Abstract
We review the species of Bidessus of Madagascar and describe Bidessus anjozorobe sp. nov. from material collected in Anjozorobe forest. Anjozorobe is part of the Anjozorobe-Angavo Protected Area, which is an important corridor of transition forest between typical eastern humid forests and the residual sub-humid forest of the Central Highlands. Bidessus longistriga Régimbart, 1895 and Bidessus perexiguus Kolbe, 1883 are widespread but endemic low-altitude species on Madagascar. Bidessus nesioticus Guignot, 1956 is an alpine species described from near the peak of the Ankaratra mountain massifs at 2500 m a.s.l. We recollected the species for the first time since its description, in Ankaratra and in a new area above 2000 m a.s.l. in the Andringitra mountain further south. Bidessus cf. nero Gschwendtner, 1933 is tentatively recorded for Madagascar for the first time but further studies are needed to test the status of mainland and insular populations. Bidessus apicidens Biström & Sanfilippo, 1986 has not been recollected on Madagascar since 1970. All species are endemic to Madagascar except potentially Bidessus cf. ceratus and Bidessus cf. nero described from Uganda and the Democratic Republic of the Congo, respectively. The older records of the two non-endemic species Bidessus complicatus Sharp, 1904 and Bidessus ovoideus Régimbart, 1895 on Madagascar could not be verified.
Highlights
Bidessus Sharp, 1882 is a genus of very small-bodied diving beetles reaching only 1.3–2.3 mm in body length and confined to the Palaearctic and Afrotropical regions (Miller & Bergsten 2016)
During his revision Biström (1985) was unable to verify either of these records or the presence of either of the two species on Madagascar
We have visited Manjakatompo Ankaratra several times but have not collected these species. We consider their occurrence on Madagascar dubious until they can be verified with specimens and have not included them in the key
Summary
Bidessus Sharp, 1882 is a genus of very small-bodied diving beetles reaching only 1.3–2.3 mm in body length and confined to the Palaearctic and Afrotropical regions (Miller & Bergsten 2016). Bidessus is most diverse in the Afrotropical region (35 spp.) where all species belong to the Bidessus sharpi species group (Biström 1985). Six species are currently known from Madagascar, four of which are endemic (Biström 1985; Biström & Sanfilippo 1986; Rocchi 1991). Its location is more westerly and at a higher elevation than most of the eastern humid forests in Madagascar. As such, it constitutes an important and unique transition forest between the eastern humid forests and the remaining fragments of the Central Highland sub-humid forests. In 2014, the first two authors surveyed water beetles in the Anjozorobe forest near Saha Forest Lodge. The second author performed more extensive surveys of Anjozorobe in 2016 and found the species again near a stream close to the first locality
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