Sensillae on the antennae of the Colorado potato beetle,Leptinotarsa decemlineata are described using scanning (SEM) and transmission (TEM) electron microscopy and compared with SEM observations of antennal sensilla inL. haldemani andL. texana. In all the three species, 13 distinct sensillar types were identified with a higher density of sensilla in the more polyphagous species,L. decemlineata than in the moderately host specificL. haldemani and the highly host specificL. texana. Cuticular specializations and the predominance of olfactory sensilla are discussed in relation to host specificity in the three species.