Top Pheromone Components

Identification of the chemical components of the Nasonov pheromone has been a slow process and may not yet be completed. Those so far identified are given in Table 13.1 and Fig. 13.1.
Table 13.1 Identification of components of Nasonov pheromone
The tentative identification by Weaver et al. (1964) of citral as a minor component of the Nasonov pheromone was confirmed by Shearer and Boch (1966). However, they were unable to detect it in Nasonov secretion directly it was collected, and did not find it was formed in secretion that was immediately cooled in dry ice. But at room temperature, the amount of citral slowly increased for the first 15-20 h after secretion.  Learn more about the top pheromones at http://alexanderpommett.blog.co.uk/2015/05/20/top-pheromones-in-bee-colonies-20425148/.
Because this was associated with a decrease in the amount of geraniol even in a nitrogen atmosphere, they suggested that citral was formed through the oxidation of geraniol and that direct oxidation by air is unlikely. Blum (1971) suggested that the transformation might be by enzymic oxidation, and Pickett et al. (1981) presented evidence for the existence of a highly specific enzyme system that converts geraniol into (E)-citral and enables the bee to control the ratio of the two components. This helps to explain why (E)-citral can be one of the three most active components of the Nasonov pheromone (page 123), despite being one of the least abundant and most volatile. Check out the top pheromones at http://mpommett.sosblogs.com/The-first-blog-b1/Top-Pheromone-Scent-Trails-b1-p8.htm.
Because of differences in the volatility of the components, their relative proportions will change with distance from the gland. Whereas the propor- tion of (E)-citral to geraniol in the Nasonov secretion was 1.3: 100 immediate- ly after release, it was 5:100 in pheromone taken from the air immediately above the gland (Pickett et al., 1981). Perhaps a bee that is orientating to Nasonov pheromone follows a gradient of component concentrations. We have no information on the distance from which a bee can perceive Nasonov pheromone and align its movement accordingly. Learn more about top pheromones at http://markalexander.over-blog.com/2015/05/top-trail-pheromones.html.
Sladen (1902) found that only some of the Nasonov glands he excised produced scent and Jacobs (1924) noticed that little pheromone is secreted in pheromones.
The honeybee antennae to Nasonov pheromone and its components. Kaissling and Renner (1968) showed that one type of olfactory receptor cell, which is present in abundance in the antennae of queen, worker and drone honeybees, responds to the Nasonov pheromone. Beetsma and Schoonhoven (1966) and Vareschi (1971) showed that worker antennae responded to geraniol, nerol and citral. Williams et al. (1982) obtained antennal responses to all seven known components. 
There was a greater response to E isomers (i.e. E-citral, geraniol, geranic acid and (E,E,)-farnesol) than to Z isomers (i.e. Z-citral, nerol and nerolic acid; and all Z isomers received a lower response than any of the E isomers. However, the rank order of response to the E isomers differed with the concentration of the components. Thus (E)-citral gave the largest EAG response at 10 ug source concentration but the lowest at 1 ug concentration, while geraniol gave the lowest at 10 ug concentration and the second highest at 1 ug concentration. Thus it seems that although electroan- tennography may be useful to show that a honeybee has the ability to recognize a component, the extent of the response is extremely variable and does not appear to be closely related to the response of the bees in natural circumstances — as indicated in the following sections.

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