Olfactory responses of stable fly (Diptera: Muscidae) larvae to volatile organic compounds

The stable fly, Stomoxys calcitrans L., is a ubiquitous, blood-feeding pest of livestock.  Effective stable fly management is heavily dependent upon larval source reduction; however, larvae develop in a wide variety of decaying material and the characterization of environmental parameters suitable for successful development is not fully complete. For example, an active microbial community is one known requirement of development, but identification of specific species or functional groups remains unknown.  Volatile organic compounds (VOC) are metabolic byproducts of microorganisms and, through behavioral assays, may assist the identification of functional groups essential for development.  Our objective was to characterize larval responses of stable flies to VOCs associated with common developmental sources. VOCs were serially diluted to 10^-6 in 48-well plates and each dilution tested with a fresh cohort of 15 larvae. Each dilution of each VOC was tested in triplicate. Behavioral responses of third-instar larvae to 29 chemicals from 9 classes were observed.  Most chemicals tested yielded no response or repulsion at high concentrations. Larvae were highly attracted to ammonia and the esters ethyl butyrate, isobutyl acetate, and ethyl hexanoate. Responses were dose-dependent; attraction decreased as VOC dilution increased. This study lays a groundwork towards understanding larval-environment interactions.