Vector Control Using Semiochemicals - Biological and Environmental Control of Disease Vectors - page 105

more likely to oviposit in the laboratory when
exposed to S. damnosum oviposition pheromone
than to a control (Wilson et al. , 2000).

devices that detect the presence of a pheromone,
thus signalling the presence (or threshold
population size) of a specifi c vector (Logan and
Birkett, 2007).

Phlebotomine sandfl ies
There is evidence that the sandfl y vector of
visceral leishmaniasis in South America,
Lutzomyia longipalpis , produces a pheromone in
the accessory glands that is secreted on to the
eggs during oviposition, which is attractive and/
or stimulatory to ovipositing females (Dougherty
et al. , 1992). This behaviour is not restricted to
one species of sandfl y: gravid females of Lu. renei
(Alves et al. , 2003), and even from a dif erent
genus, Phlebotomus papatasi (Srinvasan et al. ,
1995), lay more eggs in the vicinity of conspecifi c
eggs. Using GC-mass spectrometry, the
behaviourally active compound for Lu. longipalpis
was identifi ed as dodecanoic acid and, in both
bioassays and antennal electrophysiological
recordings, it evoked an equivocal behavioural
response in gravid sandfl ies as a whole egg
extract presented in biologically relevant
quantities (Dougherty and Hamilton, 1997).
Ovipositing Lu. longipalpis females were also
shown to be more attracted to a water extract of
rabbit faeces, and laid signifi cantly more eggs in
its presence than in a control solution (Elnaiem
and Ward, 1992). When the known oviposition
semiochemicals from rabbit faeces, hexanal and
2-methyl-2-butanol, were presented together
with dodecanoic acid in a bioassay, they elicited a
strong additive response in Lu. longipalpis
(Dougherty and Hamilton, 1997). Whether
oviposition semiochemicals can be exploited in
control or monitoring programmes for sandfl ies
is debatable, and little interest has been shown in
their development (Hamilton, 2008), but it is
possible that they could aid in the productivity of
sandfl y laboratory colonies, which, like
Simuliidae, are more dii cult to maintain in
comparison to other vector species.
Overall, pheromones can be dii cult to
characterize and often require sophisticated
analytical chemistry and synthesis. However,
the examples above demonstrate their ei cacy in
traps and their potential use in monitoring a
number of dif erent vectors. In some
circumstances, pheromones may even of er an
ef ective means of detecting specifi c vectors
through pheromone lures in trapping systems or

6.3 Evidence for Impact of
Semiochemicals on Vector
Populations

Ultimately, the aim of trapping is to reduce the
target insect population. This can be done by
using mass trapping, where the majority of
individuals are caught and simply removed from
a population. Or it can be achieved by 'lure and
kill' whereby the lure is used to bring insects into
contact with a toxicant, sterilant or pathogen.
Mass trapping can be dii cult for several reasons.
Many insects, such as mosquitoes, have a
signifi cant reproductive potential, and therefore
trapping often has a minimal ef ect on population
size. Additionally, insects can travel and
repopulate an area quicker than traps can
remove those individuals. For these reasons,
high numbers of traps are often required, which
can be expensive and time consuming to deploy
and maintain, but there are several examples of
where trapping has been used successfully to
control vectors.

6.3.1 Tsetse fl ies

There is perhaps no greater example of vector
control using semiochemicals than the control
of the tsetse fl y. Due to their very slow
reproductive rate, populations can be driven to
extinction with vector control measures much
more easily than other insects such as mos-
quitoes. For example, tsetse can be eliminated by
an intervention that removes just 3% of the
adult female population (Hargrove, 1988). This,
combined with their need to feed on hosts
regularly, approximately every 3 days, means
that semiochemicals that interfere with the
feeding process of er great potential for their
control.
Although it was originally thought that
tsetse fl ies located their hosts via visual stimuli, it
has since been demonstrated that for most tsetse
species, odour does play a role. For example, in
1974, it was shown that hosts contained inside a