Structure, ratios and patterns of release in the sex pheromone of an aphid, Dysaphis plantaginea

Stewart-Jones, Alex, Dewhirst, Sarah Y., Durrant, Lisa, Fitzgerald, Jean D., Hardie, Jim, Hooper, Antony M., Pickett, John A. and Poppy, Guy. M. (2007) Structure, ratios and patterns of release in the sex pheromone of an aphid, Dysaphis plantaginea. Journal of Experimental Biology, 210 (24), 4335-4344. (doi:10.1242/jeb.009944). (Submitted)

Abstract

Insect communication is primarily via chemicals. In
Aphidinae aphids, the structure and ratio of iridoid
(monoterpenoid) chemicals are known to be important
components of the sex pheromone. However, for enhanced
species specificity, it has been suggested that release of sex
pheromone might be restricted to a narrow time period
within the diel cycle. Here, we determine the structure,
ratios and release patterns of iridoid chemicals produced
by a serious global pest, the rosy apple aphid, Dysaphis
plantaginea. Volatiles were collected from batches of
oviparae (sexual females) and chemicals identified by
gas chromatography, mass-spectrometry and microscale
NMR spectroscopy. (1R,4aS,7S,7aR)-Nepetalactol and
(4aS,7S,7aR)-nepetalactone were detected in a 3.7:1 ratio.
To investigate timing of release, we constructed a
sequential sampling device that allowed volatile chemicals
to be captured hourly from 95 same-aged oviparae over
20 consecutive days. Release patterns of the two sex
pheromone components show that D. plantaginea oviparae
release high levels of the two components during
photophase and low levels during scotophase. Release of
the two components increased significantly during the first
3·h of photophase and thereafter remained at a high level
until the onset of scotophase. The ratio of (1R,4aS,7S,7aR)-
nepetalactol to (4aS,7S,7aR)-nepetalactone released did not
change significantly between days two to 14 of the adult
stadium, but from the 15th day onward there was a
significant decrease in the relative amount of
(1R,4aS,7S,7aR)-nepetalactol. Pheromone release was
greatest on the eighth day of the adult stadium, with up to
8.4·ng of pheromone released per ovipara per hour. This is
the first report on the full structural identification and
ratios of volatile iridoid components collected from D.
plantaginea oviparae and is also the most detailed temporal
study on sex pheromone release from any aphid species.
The lack of a temporally narrow and distinct period of very
high sex pheromone release suggests that alternative
mechanisms or factors for species recognition and isolation
may be important. Findings are discussed broadly in
relation to the biology of the aphid.

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