Electroantennogram techniques (EAGs) were employed to record olfactory responses in the antennae of the adult female stable fly, Stomoxys calcitrans (Diptera: Muscidae), to Zanthoxylum piperitum pericarp steam distillate (ZP-SD), Z. armatum seed oil (ZA-SO) and their 29 volatile constituents alone as well as binary mixture of the ZP-SD and ZA-SO with 1-octen-3-ol. The electrophysiological responses of the test materials were compared with those of DEET and 1-octen-3-ol. At concentration of 10-1 (v/v) in mineral oil, ZP-SD, ZA-SO, and all volatiles elicited EAG responses in the fly antennae except for DEET, which is extremely low volatile. ZP-SD, ZA-SO, and some of the test volatiles elicited EAG responses rather lower than 1-octen-3-ol, which showed vapor phase repellency and toxicity to the fly in our previous behavioral research. This suggests that the stable fly possesses olfactory receptor neurons responding to given repellent compounds per se. In binary mixture with 1-octen-3-ol at concentration of 10-1, ZP-SD and ZA-SO elicited 16±0.55 and 18±0.63 mV while ZP-SD, ZA-SO, and 1-octen-3-ol alone elicited responses of 14±0.45, 15.8±0.37 and 16.2±0.58 mV, respectively. Among the volatile compounds, terpinen- 4-ol, β-myrcene, α-phellanderene, citronellal, and limonene oxide elicited 80 – 96% relative EAG amplitude compared to 1-octen-3-ol as a reference (100%). Based on structure-activity relationships, constituents having aldehyde moiety elicited bigger EAG responses than those of alcohol or ether one. The perception in the fly antenna to plant volatile compounds exhibited complicated patterns of olfactory responses. Current and future directions of this study on sensory processing mechanisms underlying repellent behaviors will be discussed.

The repellent constituents of essential oils from Zanthoxylum armatum (Rutaceae) seed and Zanthoxylum piperitum fruit against female Stomoxys calcitrans were analyzed by gas chromatography and gas chromatography-mass spectrometry. The repellency of two Zanthoxylum essential oils and 11 oil compounds against female S. calcitrans was examined using a skin bioassay. Results were compared with those of the most widely used repellent DEET. Both Z. armatum seed and Z. piperitum fruit oils provided complete and good protection from fly bites for 30 min at 0.4 and 0.2 mg/cm2, respectively. At 0.05 mg/cm2, both oils gave ca 70 and 40% repellency at 30 and 60 min post-treatment, respectively, whereas DEET provided 83 and 73% protection. Of test compounds, cuminaldehyde at 0.05 mg/cm2 gave 92 and 69% repellency at 10 and 30 min post-treatment, respectively, whereas 1,8-cineole, and citronellal provided approx. 76% repellency at 10 min. The Zanthoxylum oils and their constituents, particularly cuminaldehyde, merit further study as potential insect repellents for the protection from humans and domestic animals from biting and nuisance caused by S. calcitrans.