A review of the New Guinea species of Laccophilus Leach 1815 with notes on regional melanism (Coleoptera Dytiscidae)

Laccophilus bapak n. sp., L, ekari n. sp., L. papuanus n. sp. and L, ramuensis n. sp. are described from New Guinea. The sister-species of L, bapak is L, seminiger Fauvel 1883, whereas L, papuanus is close to L. univittatus Regimbart 1891. L, ekari and L, ramuensis are both close to L. transversalis Regimbart 1877. There is strong evidence that many species-groups of Laccophilus Leach 1815 as currently delimited are paraphyletic, and features supporting this hypothesis are briefly discussed. Apically bifid metatibial spurs are an apomorphy of the genus Laccophilus, thus the acute spurs in L. bapak are interpreted as a character reversal according to the cladistic analysis carried out here. Recent New Guinea localities are listed for all the Laccophilus species. Features for the identification of L, seminiger and L, univittatus are also given. Twelve species of Laccophilus are known at present from New Guinea, but the report of four additional species by GUEORGUIEV & ROCCHI 1993 (L, decoratus Boheman 1858, L, parvulus Aube 1838, L. sharpi Regimbart 1889, and L, ritsemae Regimbart 1880) requires confirmation. The distribution ranges of all New Guinea species are summarized on maps. We also found evidence that Philodytes Balfour-Browne 1939 cannot be a valid genus but is a subgenus of Laccophilus and the occurrence of acute metatibial spurs in its only species, L, umbrinus Motschulsky 1859 is due to reversal. An unusually high proportion of the dytiscid fanua of New Guinea, including Laccophilus species, is composed of dark or melanistic forms. It is postulated that the shading of the lentic habitats by the luxuriant vegetation favours the occurrence of dark coloured water beetles.