Repellency of Various Oils and Pine Oil Constituents to House Flies (Diptera: Muscidae)

Comparative repellency of pine, mineral, motor, and silicon oil to house flies, Musca domestica L., was tested. In binary choice bioassays with flies feeding on 20 microliter of watery honey solutions mixed with (treatment) or without (control) 10 microliter of one of the oils under investigation, only pine oil completely suppressed feeding and remained inhibitory even after 24 h. Approaching pine oil-treated honey solution, 95% of flies were repelled at a distance >6 mm from the source. Analysis of pine oil volatiles by coupled gas chromatographic-electroantennographic detection (GC-EAD) analysis revealed 5 antennally active compounds, 4 of which were identified by coupled GC-mass spectrometry as myrcene, p-cymene, gamma-terpinene, and (+/-)-linalool. Treatment of honey solution with pine oil, the 4 compounds singly, or in quaternary combination at 10 microliter each, equally and significantly reduced the number of feeding flies compared with untreated honey solution. At an amount of 1 microliter, only the linalool treatment inhibited feeding. In binary choice experiments both feeding and oviposition were significantly reduced on linalool-treated sources. Because fly maggots naturally develop in and rely on microbe-rich organic sources, gravid females may perceive and avoid potential oviposition sites that are rich in antimicrobial compounds such as linalool.