Page 5 - Volume 3, Issue 2, July 2010

© Benaki Phytopathological Institute
Mosquito oviposition aggregation pheromone 35
ral form, but also for the erythro enantiom-
ers and for all four diastereoisomers of the
6-acetoxy-5-hexadecanolide.
1. Oviposition Bioassays
1.1. Egg-associated pheromone bioas-
says and observations
The first oviposition-inducing activity,
caused by an egg-associated pheromone, was
reported in the early ’70s by Osgood (1971)
(Table 1). This was demonstrated with Culex
tarsalis employing 3 densities of egg rafts
and also by split-airstream olfactometer. Pre-
liminary analysis of the droplet indicated that
this new chemical was a lipid, with low va-
por pressure and consisted of a mixture of es-
trolide 1,3-diglycerides, that were composed
of mono- and diacetoxy fatty acids (Osgood,
1971; Starratt and Osgood, 1972; Starratt and
Osgood, 1973). Further studies concluded that
the conclusion that the apical droplet of the
mosquitoes’ eggs contains straight-chain ali-
phatic fatty acids of C-12, C-14, C-16 and C-18.
In addition, C-12 β-OH and C-14β-OH fatty ac-
ids were found, with the latter to be the major
component (Aharoni and Zweig, 1973).
The use of non-specific natural attractants
(e.g. polyethylene or simulated egg rafts)
shows no effect in oviposition behavior. Also,
neither the presence of larvae, pupae and
trapped adults, nor the 5% sucrose solution
induced any response (Bruno and Laurence,
1979) (Table 2). In the same report, studies on
the stability of the apical droplet indicated
that, when the material was kept at 21°C in the
light, it remained bioactive for 21 days, where-
as when kept at 4°C in the dark, the material
appeared to be mainly inactive for 28 days.
Table 1. Number of egg rafts laid from gravid females of Culex mosquitoes when the test
bowl was primed with egg rafts of the same or another species. Reference: Bruno and Lau-
rence (1979) modified by Clements (1999).
Test species Priming species Replicate
tests
No. of
prim-
ing egg
rafts
Total no. of egg
rafts laid in test
bowls
Total no. of egg rafts
laid in control bowls
Cx. quinquefasciatus Cx. quinquefasciatus 10 1 374 46
Cx. pipiens 10 1 333 163
Cx. tarsalis 17 1 312 155
Cx. tarsalis Cx. tarsalis 19 1 225 160
Cx. tarsalis 10 10 273 113
Cx. quinquefasciatus 14 1 145 124
Cx. quinquefasciatus 10 10 295 115
Table 2. The response of Culex mosquitoes to factors other than egg rafts.
Test material Replicate
tests
Total no. of egg
rafts laid in test
bowl
Total no. of egg
rafts laid in con-
trol bowl
Reference
polyethylene egg rafts 10 58 180 Bruno and Laurence (1979)
card egg rafts 12 322 160 Bruno and Laurence (1979)
1st-instar larvae 10 105 111 Bruno and Laurence (1979)
4th-instar larvae 10 408 337 Bruno and Laurence (1979)
pupae 10 376 138 Bruno and Laurence (1979)
5% sucrose 10 84 148 Bruno and Laurence (1979)
artificial white egg rafts 10 161 152 Osgood (1971)
artificial black egg rafts 10 153 152 Osgood (1971)