Periodicity in the Quantity and Ratio of Pheromone Components in Volatile Emissions from Virgin Females of the Spotted Stalk Borer Moth Chilo partellus (Swinhoe)
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Volatile sex pheromone was collected from the extruded pheromone gland of females of the spotted stalk borer moth Chilo partellus and trapped on glass wool. The pheromone was collected from females on the night of eclosion, 1st, 2nd, 3rd and 5th scotophases thereafter. The female sex pheromone components, (Z)-11-hexadecenal and (Z)-11-hexadecen-1-ol were identified by gas chromatography co-injection with synthetic authentic compounds and confirmed by GC-mass spectrometry. The quantity of the pheromone components was determined by comparison of GC peak areas with that of (E,Z)-3,13-octadecadienyl acetate as an internal standard. Periodicity in the pheromone emission was uni-modal with a peak about the 7-10 h into the scotophase. During the peak period, (Z)-11-hexadecenal was emitted at a rate of 43.1, 30.9, 21.5 and 16.5 ng/30 min on the day of eclosion, 1st, 3rd and 5th scotophases, respectively. A marked reduction in the release rate of the pheromone components was recorded with progressing age of females. This decrease was faster for (Z)-11-hexadecen-I-ol than for (Z)-11-hexadecenal which resulted in a spectacular shift in the ratio (Z)-11-hexadecen-I-ol ranging from about 1:1 at eclosion to 9:1, 22:1 and 32:1 in the 1st, 3rd and 5th scotophases, respectively. The age-dependent shift in both release rate and ratio of pheromone components corresponds to the change in attractiveness of females to mate-searching males. The periodicity in the quantity and blend ratios of C. partellus pheromone is discussed in light of development of a pheromone-based bait for the management of this pest.