Melophagus ovinus (Linnaeus 1758), Hippobosca equina Linnaeus, 1758, and Hippobosca longipennis Fabricius, 1805 (Diptera: Hippoboscidae) are economically and medically important ectoparasites that can act as mechanic vectors of pathogens and cause myiasis in both human and domestic animals. As essential olfactory organs, antennae of these adult hippoboscids were examined using stereoscopic and scanning electron microscopes. General morphology of the antenna is provided in detail, combined with distribution, types, size, and ultrastructures of antennal sensilla. On the antennal funiculus, two types of sensilla are observed, including basiconic sensilla and coeloconic sensilla. Four common characters are shared among the three species: (1) the scape is either obsolete or fused with the fronto-clypeus; (2) branched antennal structures (branched pedicellar microtrichiae and branched arista with only one segment) are detected; (3) the enlarged antennal pedicel completely envelops the antennal funiculus; and (4) less types of sensilla on funiculus. Disparity and diversity of the antennal and sensory structures are analyzed from the phylogenetic and functional perspective. We suggest that hippoboscids are potential model for the study of the function of coeloconic sensilla in Calyptratae.

Lucilia sericata (Meigen) is a cosmopolitan synanthropic fly of forensic and medical importance, which can work as a mechanic vector of pathogens or cause myiasis of both human and sheep. As essential olfactory organs, antennae of adult L. sericata were examined with stereoscopic microscope, scanning electron microscope, and laser scanning confocal microscope. On antennal scape and pedicel, both microtirchiae and several bristles are detected, while another two structures, setiferous plaques and pedicellar buttons, are also found on the antennal pedicel. Seven subtypes of antennal sensilla are observed on antennal funiculus including one subtype of trichoid sensilla, two subtypes of basiconic sensilla, two subtypes of coeloconic sensilla, and two subtypes of sensory pits. Size and density of the former four types of sensilla on antennal funiculus are measured. Three distinctive sensillar characters of L. sericata are detected, which may contribute to greater olfactory sensitivity of this species and their wide distribution throughout the world. Unlike the common poreless pedicellar button with mechanoreceptor function, every pedicellar button in L. sericata is perforated by three pores, which might indicate potential chemoreceptor function of this structure. Besides, another unique feature is greater number of setiferous plaques in genus Lucilia than calliphorids of other genera. Expect for the common sensory pits with basiconic or basiconic-like sensilla in them, sensory pits filled with rarely described coeloconic-like sensilla are founded in L. sericata as well. After comparison with previous equivalent findings, the functions of these specific structures are discussed according to the life history of this calliphorid.

Blow fly, Triceratopyga calliphoroides Rohdendorf, is a common and synanthropic species of medical and forensic significance in eastern Asia. Field monitoring studies have indicated that olfaction system plays an important role in guiding the behavior of insect species. To further our understanding of fly olfaction, scanning electron microscopy (SEM) and laser scanning confocal microscopy (LSCM) are applied to examine the sensillar morphology of adults, with an emphasis on sensory pit and sacculus. Both microtrichiae and several mechanoreceptors are detected on antennal scape and pedicel. Except for these two structures, pedicellar buttons are also found in antennal pedicellar depression after the separation of antennal pedicel and funiculus. Eight types of antennal sensilla are observed on external surface of antennal funiculus (one type of trichoid sensilla, three types of basiconic sensilla, three types of coeloconic sensilla, and one type of clavate-like sensilla), while two types (one type of basiconic sensilla and one type of coeloconic-like sensilla) are detected at the inner surface of sensory pits or sacculus. As the first to investigate cuticular invaginations of blow flies via paraffin section, the internal structure of abundant sensory pits and an excessively complex sacculus on antennal funiculus are revealed. After comparison to other species previously studied, this phenomenon is proved to be the most unique feature of T. calliphoroides, armed with a discussion on its morphology, function, and possible evolutionary implications.

Rhinoestrus purpureus (Brauer, 1858) (Diptera: Oestridae) is an economically important parasite that can cause severe nasal myiasis in equids or even attacking humans. The antennae of R. purpureus were examined using stereoscopic microscopy and scanning electron microscopy. The general morphology was provided detailedly, together with distribution, type, size, and ultrastructure of antennal sensilla. All the three antennal segments, antennal scape, pedicel, and funiculus, are interspersed by microtrichiae. Only mechanoreceptors are detected on antennal scape and pedicel. On antennal funiculus, three types of sensilla were observed, including basiconic sensilla, coeloconic sensilla and clavate sensilla. Two features are characterized of this host-specific bot fly: (1) numerous sensory pits with branched basiconic sensilla on antennal funiculus and (2) the absence of trichoid sensilla. The function of these distinctive traits are discussed in association with the life history. We suggest that more sensory pits with branched sensilla could increase the sensitivity of olfactory system for host orientation, while the capability of pheromone identification might be reduced due to the absence of trichoid sensilla. Besides, we support both thermo- and chemo-functions of coeloconic sensilla.

Hypoderma lineatum (Villers, 1789) (Diptera: Oestridae) is a hypodermosis fly that has resulted in great economic losses worldwide. The antennae of cattle grub males and females were examined through stereoscopic microscopy and scanning electron microscopy to reveal the general morphology, combined with distribution, type, size, and ultrastructure of the antennal sensilla. All of the three antennal segments (antennal scape, pedicel, and funiculus) possess microtrichiae on their surface. Mechanoreceptors only exist on the antennal scape and pedicel. The antennal funiculus presents four types of antennal sensilla: trichoid, basiconic, coeloconic, and clavate sensilla. Three distinctive characters of H. lineatum are obvious: (1) the relatively slender, flexible, and equal-height mechanoreceptors; (2) the enlarged antennal pedicel, and numerous antennal sensory pits and pit sensilla on the antennal funiculus; and (3) all types of antennal sensilla clustered in sensory pits, respectively. Additionally, the enlarged antennal pedicel and abundant sensory pits and pit sensilla might facilitate odor detection, enhance olfactory sensitivity and accuracy, and also protect the fragile antennal sensilla from mechanical irritation or damage.