Abstract: The ultrastructure of olfactory sensilla on antennae of Holotrichia diomphalia adult was studied using SEM and TEM. The results showed that the olfactory sensilla concentrated on antennal lamellae and all these sensilla were situated on the sunken cavity formed by antennal cuticle depressions. Two types of olfactory sensillum on lamellae were found both sensilla basiconca (S. ba) and sensilla placodea (S. pl). Based on the difference of cone and plate shape, S. ba was further classified into four subtypes, and S. pl. into five subtypes. The cuticle of olfaction sensillum was single-walled, with a plenty of pores and pore tubules. The number of neuron in olfactory was inconsistent, including one olfactory receptor neuron (ORN), two ORNs and three ORNs. The length of each lamella on antenna in the male was longer than that in the female, and the total number of sensilla in the male was far more than that in the female. The number of S. pl showed no obvious difference between two sexes, but the number of S. ba in the male was far more than that in the female, about nine times that of the latter. It is so inferred that the S. ba is the sensillum used for reception of pheromone and S. pl is used for reception of plant odors.

Key words: Holotrichia diomphalia, olfaction sensillum, ultrastructure, sexual dimorphism, SEM, TEM