We investigated the antennal morphology, sensillar types, and sensillar distribution in the dark (“melanic”) and the light (“succinea”) forms of Asian multicolored ladybirds, H. axyridis, using scanning electron microscopy (SEM). Antennae of both sexes of H. axyridis consist of the scape, pedicel, and nine flagellomeres. Seven sensillar types are distinguished: four types of sensilla trichodeae (s.tr), four types of sensilla basiconicae (s.ba), four types of sensilla chaetica, and one type each of sensilla coeloconica (s.co), sensilla sporangium (s.sp), sensilla placoidea (s.pl), and Böhm bristle (s.bm). Sensilla trichodea are the most numerous; sensilla chaetica are the next most abundant. The number of other sensillar types is greatly reduced. On the tip of the 9th flagellomere, various types of sensilla are densely packed, except for s.bm and s.pl. No remarkable differences are found in the antennal size, shape, and sensillar types between the melanic and succinea forms of H. axyridis, but there is a difference in the total number of s.tr.2 between the two forms. No differences are found in the antennal size and the total number of sensillae between males and females of each form. According to the distribution of sensillae and sensillar functions reported in the past, s.tr are presumed to be pheromone receptors in H. axyridis, s.ch may function as mechanoreceptors and chemoreceptors, s.ba and s.co are postulated as plant volatiles receptors and chemo-, thermo-, or hygroreceptions, respectively, and s.bm may be related to perceiving the antennal position and movement.
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