Vector Control Using Semiochemicals - Biological and Environmental Control of Disease Vectors - page 100

(e.g. Cx. pipiens quinquefasciatus , Cx. univattus , Cx.
theileri , Cx. rubinotus and Mansonia africana ) were
caught using this synthetic blend. It therefore
shows promise as a tool for trapping a wide range
of important disease vectors in the fi eld.
There are several potential advantages of
using odour-based trapping over other mosquito
sampling tools such as Center of Disease Control
(CDC) light traps and human landing catch. For
example, they can replace human subjects as
baits, thus reducing the ethical implications of
using human subjects for collecting mosquitoes
(Mukabana et al. , 2012). By using traps, better
consistency can be achieved as well as cost
ef ectiveness, factors that have restricted the
development of sustainable mosquito sur-
veillance systems, especially in resource-limited
countries. Traps could also be combined with
existing control tools such as insecticides and
repellents to create a push-pull strategy (Logan
and Birkett, 2007).

site-specifi c attractant kairomones, for monitor-
ing or control of a range of dif erent disease
vectors.

Culex mosquitoes
Culex mosquitoes lay their eggs in boat-shaped
clusters that are held upright and together by
interlocking tubercules on the exchorion of each
egg (Beament and Corbet, 1981). At the top of
every egg, an apical droplet begins to form that
reaches a maximum size at 18 h post-oviposition
(Laurence and Pickett, 1985). Apical droplets
have surfactant properties, which may reduce
the surface tension of the water and aid raft
fl otation (Iltis and Zweig, 1962) and, for Cx.
pipiens at least, may of er protection against
predatory ants (Hinton, 1968). A further role of
the apical droplet was proposed following
observations that gravid females of Cx. tarsalis
(Osgood, 1971) and Cx. quinquefasciatus (Bruno
and Laurence, 1979) were attracted to conspecifc
egg rafts. The behavioural activity was shown to
be elicited by a chemical present in the apical
droplets, identifi ed as erythro-6-acetoxy-5-
hexadecanolide (Laurence and Pickett, 1982)
and, as Cx. tarsalis were attracted to Cx.
quinquefasciatus rafts, indicating that attractancy
was interspecifi c (Bruno and Laurence, 1979).
This has been referred to as the ' Culex oviposition
pheromone' in much of the literature.
Since the absolute confi guration of the
pheromone has been confi rmed, and the
synthesized (-)-(5R,6S)-6-acetoxy-5-hexadec-
anolide enantiomer was shown to exhibit
biological activity comparable with the natural
material (Laurence et al. , 1985), many research
groups have attempted to synthesize the
pheromone as simply and cheaply as possible
(Dawson et al. , 1990; Tolstikov et al. , 1992;
Bonini et al. , 1995; Gravierpelletier et al. , 1995;
Couladouros and Mihou, 1999; Olagbemiro et
al. , 1999; Gallos et al. , 2000; Sun et al. , 2005;
Ikishima et al. , 2006; Sabitha et al. , 2006).
Perhaps the most novel innovative method that
could be feasibly upscaled for use in resource-
poor and disease-endemic areas of the world
used a fi xed oil extracted from the seeds of the
summer cypress plant, Kochia scoparia
( Chenopodiaceae ), and produced a cheap product,
with activity comparable to that of the pure
synthetic

6.2.2 Oviposition semiochemicals

As described previously (see Lorenz et al. ,
Chapter 4, this volume) and elsewhere (McCall
and Cameron, 1995), most arthropod disease
vectors do not exhibit brood care, so the selection
of suitable oviposition sites by gravid females
can contribute signifi cantly to the survival of
their progeny. The choice of an oviposition site
and subsequent deposition of eggs by gravid
females is infl uenced by a variety of olfactory,
visual and tactile cues (Clements, 2000; McCall,
2002). Pheromones and site-specifi c kairomones
that af ect the oviposition behaviour of mos-
quitoes (Navarro-Silva et al. , 2009) and other
haematophagous insects (McCall, 2002;
Seenivasagan and Vijayaraghavan, 2010) have
been reviewed recently. While such semio-
chemicals may operate either as deterrents or
stimulants over short distances, they can also
act as repellents or attractants over longer
distances (McCall, 2002). An optimum lure may
attract a large number of ovipositing females to
selective breeding sites, thus reducing the
amount of insecticide required to achieve
control, thereby proving to be more cost-ef ective
than some alternative strategies. This section
will address the potential of attractant ovi-
position pheromones, and their interaction with pheromone (Ogbunugafor and