The partially sympatric Colorado potato beetle (CPB), Leptinotarsa decemlineata (Say), and the false potato beetle (FPB), Leptinotarsa juncta (Germar), were shown to possess a series of reproductive barriers that protect species integrity. A strongly stereotyped sequence of courtship behaviour insures that more than 85% of encounters between these congeneric species are terminated before copulation. The courtship behaviour of the FPB, described here for the first time, is similar to that for the CPB. However, the male FPB is more likely to walk off the female FPB and will repeat antennal tapping more frequently than the CPB before moving on to palp tapping and mating. Observations suggest that both species first use antennal tapping for an initial olfactory assessment of the object as a female insect of a given family or species and palp tapping for final sex recognition. If courtship behaviour fails to break up the hybridization pairs, there is no mechanical barrier to mating and sperm transfer takes place. However, there is gametic mortality. The FPB is more fecund than the CPB and seems less dependent than the CPB on multiple matings to reach its full reproductive potential.