The first-instar larva of Meladema coriacea Laporte, 1835 is redescribed, and that of Neostutopterus hornii (Crotch, 1873) is described for the first time. A generic key to first-instar larvae of Colymbetini is presented, but it does not include the monobasic New World genera Bunites Spangler and Hoperius Fall, whose young larvae are unknown. Polarity is determined for a set of 12 characters of first-instar larvae, and the distribution of character states among genera is used to reconstruct phylogeny. It suggests that Meladema Laporte and Neoscutopterus J. Balfour-Browne together form the most derived lineage of the Colymbetini, whereas Colymbetes Clairville is the least derived genus.
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