Chromosome numbers for six species ofMonoxia(Coleoptera: Chrysomelidae: Galerucinae) fall in two main groups: species with 9 or 10 bivalents and species with 16 or 19 bivalents. The sex determination system is Xyr(possibly neoXY). The intrageneric classification ofMonoxiais now based on congruent cytological, morphological, and host plant feeding information.