No abstract

Electroantennogram, Gas Chromatography, Pheromones, (E,Z)-7,9-Dodecadienyl Acetate, Lobesia botranaA gas chromatographic detector is described which uses an insect antenna as a sensing element and permits the continuous monitoring of pheromones and other compounds with olfactory activity. In high-resolution gas chromatography allowing separations of positional and geometrical isomers, the electroantennographic detector gives precise information on the retention times of active com pounds and permits the analysis of insect pheromones with exceedingly small amounts of material.

Pheromone gland extracts of codling moth females were examined by gas chromatography coupled with mass spectrometry and electroantennography. Nine compounds elicited antennal activity: the main pheromone compound codlemone (E,E)‐8,10‐dodecadienol, the E,Z and Z,E isomers of codlemone, codlemone acetate (E,E)‐8,10‐dodecadienyl acetate, codlemone aldehyde (E,E)‐8,10‐dodecadienal, the monounsaturated alcohols (E)‐8‐dodecenol and (E)‐9‐dodecenol, and dodecanol. In wind tunnel experiments, addition of dodecanol, the E,Z isomer of codlemone and codlemone acetate augmented male attraction to codlemone at the proportions found in female glands. Larger amounts of the E,Z isomer of codlemone and codlemone acetate had a strong antagonistic effect on male attraction. The identification of pheromone synergists in codling moth is of importance for the development of pheromone‐ based control methods.

Coupled gas chromatographic-electroantennographic detection analyses of ovipositor extracts of calling Contarinia nasturtii females revealed two compounds that elicited responses from antennae of male midges. Using synthetic reference samples, these components were identified by gas chromatography mass spectrometry and enantioselective GC as (2S,9S)-diacetoxyundecane and (2S,10S)-diacetoxyundecane. In addition, trace amounts of 2-acetoxyundecane were found in ovipositor extracts, and the (S)-enantiomer was synthesized. When tested in the wind tunnel, a blend of 5 ng (2S,9S)-diacetoxyundecane and 10 ng (2S,10S)-diacetoxyundecane (mimicking the ratio found in the extracts) did not attract any of the males tested, but when 0.1 ng (S)-2-acetoxyundecane was added to the blend, 86.8% of the males were attracted to the bait. Three-component blends with lower or higher relative concentrations than 1% of (S)-2-acetoxyundecane [relative to (2S,10S)-diacetoxyundecane] were less attractive. In a field trapping experiment with released laboratory-reared C. nasturtii adults, traps baited with 500:1000:10 ng of (2S,9S)-diacetoxyundecane/(2S,10S)-diacetoxyundecane/(S)-2-acetoxyundecane applied to rubber septa or dental cotton rolls were tested. Traps without dispensers were used as controls. All three treatments were tested at 20 and 50 cm above ground. The estimated recapture rate was 30-50%, and 81.9% of the recaptured males were caught in traps positioned at 20 cm above ground, and 88.4% in traps with dental cotton rolls as dispensers.