Page 4 - Volume 3, Issue 2, July 2010
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© Benaki Phytopathological Institute
Mihou & Michaelakis
34
Introduction
In species with aquatic larvae, maternal re-
productive success depends on the selec-
tion of a suitable site for depositing their
eggs. This selection determines the continu-
ation of such a species since, once in a hostile
environment, immature stages are unable to
move to another more suitable habitat and
will perish (Mokany and Shine, 2003). The se-
lection of the appropriate oviposition site by
a gravid female mosquito is influenced by an
oviposition aggregation pheromone. Each
egg releases this pheromone, which acts as
a signal to other
Culex
female adults to ovi-
posit in the same water body.
Species of
Culex
,
Culiseta
, and
Uranotae-
nia
lay their eggs in raft (Figure 2, egg rafts)
(Clements, 1999). These egg rafts, depending
on the species, consist of 100 to about 400
eggs and are boat-shaped; the lower surface
of each raft is convex and larger while the
upper surface is concave and smaller (Cle-
ments, 1999; Christophers, 1944). Each egg
forms a small droplet at the posterior. The
first report on the existence of this droplet
was in 1944 by Christophers (1944) who no-
ticed that all egg droplets are of similar size
and appearance, they appear shortly after
oviposition and, if removed, they are formed
again. Further studies reported that the api-
cal droplet has also a righting function, turn-
ing capsized egg rafts to their normal po-
sition on the water surface (Iltis and Zweig,
1962) and that eggs are joined together by
inter-digitation of the regularly spaced tu-
bercles (Beament and Corbet, 1981).
The chemical composition of the droplet
did not become known, until almost 40 years
after it was first described. A series of chem-
ical syntheses and bioassays confirmed that
the droplet contained a pheromone, whose
chemical structure was found to be the (–)-
(5
R,
6
S
) isomer of 6-acetoxy-5-hexadecan-
olide, 1a, (Laurence and Pickett, 1982 and
1985) (see in Figure 3 all 4 diastereoisomers).
Alongside the discovery of this pheromone,
equally important and interesting have also
been the various synthetic approaches that
have been developed, not only for its natu-
Figure 2.
A typical mosquito egg raft measuring 11 mm in
length.
Culex
mosquitoes lay their eggs one at a time, sticking
them together in the form of a “raft”.
Source of figure:
Figure 3.
The four diastereoisomers of 6-acetoxy-5-hexadecanolide.
