ANTENNAL SENSILLA AND SEXUAL DIMORPHISM OF THE ADULT LADYBIRD BEETLE SEMIADALIA-UNDECIMNOTATA SCHN (COLEOPTERA, COCCINELLIDAE)

The antennal receptors of the adult male and female ladybird beetle, S emiadalia undecimnotata (Coleoptera : Coccinellidae), were examined by scanning and transmission electron microscopy. Twelve types of recept ors were characterized and grouped into 5 morphological classes: Bohm, trichoid, coeloconic, basiconic, and chetiform sensilla. Sensory func tion was determined on the basis of sensillar ultrastructure and elect rophysiological response. Olfactory sensilla are confined in both sexe s to the 2 terminal antennal segments. In contrast, gustatory and mech anosensitive organs are present along the entire length of the antenna e. Sexual dimorphism of antennal receptors is limited to the latter 2 functional classes. The principal characteristics of this dimorphism a re the following: a) males possess 540 sensilla (all types), while fem ales possess only 500; b) males exhibit 2 types of taste receptors not present in females; c) females exhibit one type of mechanoreceptor ab sent in males; d) the 3 sex-specific types of sensilla, which occupy t he same position in males and females, are confined to the inner side of the antennae. The possible role of male-specific sensilla in inters exual communication is discussed.