Characterization of olfactory sensilla of Stomoxys calcitrans and electrophysiological response to odorant compounds associated with their host and oviposition media

Stable flies, Stomoxys calcitrans (Diptera:Muscidae)are economically important biting flies that have caused billions of dollars in losses in the livestock industry. Field monitoring studies have indicated olfaction may play an important role in host location. To further our understanding of stable fly olfaction, we examined the electron microscopic(SEM)techniques. Four major types of sensilla were found and classified as:1)basiconic sensilla, 2)trichoid sensilla,3)clavate sensilla, and 4)coeloconic sensilla. No significant differences in abundance(total numbers)of sensilla were observed among these sensilla types between male and female stable flies,except the medium-sized trichoid sensilla. The distinctive pore structures found on the surface of basiconic sensilla and clavate sensilla suggest they are olfactory sensilla,with chemoreceptory functions. No wall pores were found in both trichoid and coeloconic sensilla suggesting these two types of sensilla may function as mechano-receptors, though the latter one was also described as thermo-hygroreceptors from other fly species. Details in distributions of different sensillar types located on the funicle of the stable fly antennae were also introduced. Electroantennogram results indicated significant antennal responses to host associated compounds. The importance of stable fly olfaction relative to host and host environment seeking are also discussed. This research provides valuable new information that will enhance future developments in integrated stable fly management.