Résumé
Eight species of Lasioglossum are recorded from New Caledonia. A new cleptoparasitic and endemic subgenus with one new species, Lasioglossum (Parachilalictus n. subg.) neocaledonicum n. sp., is described. The following new endemic species of the subgenus Chilalictus are described : Lasioglossum (Chilalictus) alticola n. sp., L. (C.) tchambae n. sp. and L. (C.) webbi n. sp. A new subspecies, Lasioglossum (Chilalictus) polygoni austrocaledonicum n. ssp. is described from New Caledonia and Australia. The Australian species L. (Chilalictus) lanarium (Smith 1853) and L. (C.) instabilis (Cockerell 1914) are recorded for the first time from New Caledonia. Lasioglossum (Parasphecodes) sulthicum (Smith 1853) is the first species of this Australian subgenus to be recorded from New Caledonia. The emergence of cleptoparasitism and speciation in this insular situation are discussed. The cleptoparasitism of this new subgenus Parachilalictus n. subg. can be demonstrated by examining a set of convergent morphological characters among groups of parasitic Halictids, such as a reduced pollen collecting brush on the hind legs and flattening of the keel of labrum. The strong resemblance of Parachilalictus n. subg. to endemic species of Chilalictus and its absence in Australia suggests recent and local speciation. The two new endemic species described in the subgenus Chilalictus, from which Parachilalictus n. subg. might have emerged, both have a mountain distribution. Within the L. polygoni species-complex, speciation is expressed through variation in the density and strength of punctuation. At low altitude and along the drier west coast, we find the typical subspecies polygoni. At altitude ranging from 5 to 1150m, there are clearly two other subspecies. The new subspecies austrocaledonica is found only in the southern part of the island, in an open "maquis" environment, while the subspecies delobeli Munzinger & Pauly 2003 has a wider distribution on the mountains of the east, and was mainly seen in forest tracks in the rainforest. The latter subspecies occurs also in Australia.