Repellency of various oils and pine oil constituents to house flies (diptera: muscidae)
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Comparative repellency of pine, mineral, motor and silicon oil to house flies, Musca domestica L., was tested in 10- minute binary choice bioassays, each employing 20 caged, 4-5 day-old flies. Testing the number of flies feeding on 20 ul of watery honey solutions (HS) mixed with (treatment) or without (control) 10 ul of one of the oils under investigation, only pine oil completely suppressed feeding and remained inhibitory even after 24 hours. Approaching pine oil-treated HS, 95% of flies were repelled at a distance > 6 rom from the source, indicating that recognition of repellent constituents was based on olfaction rather than contact chemoreception. Analysis of pine oil volatiles by coupled gas chromatographic-electroantennographic detection (GC-EAD) revealed 5 antennally-active compounds, 4 of which were identified by coupled GC-mass spectrometry as myrcene, paracYmene, gamma-terpinerie and linalool. Repellency of these compounds alone or in combination was demonstrated in a 5-replicate experiment employing one treatment per cage with 50 flies each. At a 10 ul dose, significantly lower proportions (P < 0.05) of flies fed on HS treated with pine oil or one of the four pine oil constituents. At a 1 ul dose 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 percieve and avoid potential oviposition sites that are rich in antimicrobial compounds such as linalool.