Vector Control Using Semiochemicals - Biological and Environmental Control of Disease Vectors - page 97

1996). The chain of behavioural events usually
begins with long-range activation and
attraction, followed by short range attraction,
landing (and possible arrestment), probing,
feeding and engorgement.
The initial phase of the host-seeking
response typically starts with 'fl ight activation'
or 'ranging behaviour' (Gibson and Torr, 1999).
Flight activation occurs when the insect is
stationary and comes into contact with host
stimuli as a host comes into close vicinity or
the wind direction changes and carries volatile
host-odour molecules to the insect. Ranging
behaviour occurs when a fl ying insect detects
host stimuli and fl ies upwind or downwind in
order to maximize the chance of encountering a
host. In this phase, long-range cues that mediate
upwind anemotaxis are important in the
successful location of a vertebrate host (Gibson
and Torr, 1999). Semiochemicals that emanate
from a host are carried downwind in the form of
a large, undisrupted plume with intermittent
pockets of exhaled breath and a continuous
plume of skin emanations carried by convection
currents (Carde, 1996; Geier et al ., 1999). Once
host kairomones have been detected downwind,
long range responses occur, where upwind
fl ight is modulated by odour-mediated anemo-
tactic, optomotor anemotactic, orthokinetic
and klinokinetic responses (Kennedy, 1978).
Changes in fl ight speed, turning angle and
angular velocity may help insects to follow the
host odour to its source by entering and leaving
the plume. When the insect is in close vicinity to
its host, short-range behaviours such as changes
in fl ight speed, turning angle and landing occur
(Gibson and Torr, 1999).
As host-derived semiochemicals can be
involved in all of the behaviours described above,
they of er an excellent opportunity for exploit-
ation into traps for surveillance or control.
Indeed, research in vector chemical ecology has
focused on the identifi cation of kairomones from
vertebrate hosts in an attempt to replicate the
complex array of semiochemicals that char-
acterize the host. Kairomones can emanate from
various locations on the vertebrate including
breath, skin (which may include gland secretions
and breakdown products of microorganisms),
urine and faeces. Several hundred potential
kairomones can be produced by any one host,
and it is therefore an extremely complex process

to determine which ones are relevant and should
be incorporated into an ef ective lure.
Understanding the role of these chemicals
allows for the development of synthetic blends
that can be used as lures to provide a better
understand of host-seeking behaviour and to be
exploited in traps for surveillance or control
through mass trapping.
Numerous semiochemicals have been
identifi ed that are capable of modifying insect
behaviour. However, this chapter will not
provide an overview of all them (Logan and
Birkett, 2007), instead it will focus on the
semiochemicals that have been utilized suc-
cessfully in relation to surveillance or control of
tsetse fl ies, mosquitoes and Culicoides midges -
vectors of many pathogens that cause diseases
including trypanosomiasis, malaria, dengue
fever, yellow fever and bluetongue virus to name
but a few.

Carbon dioxide
One of the most common semiochemicals used
in traps is carbon dioxide (CO 2 ), a major
component of vertebrate breath, which plays
a key role in the host-seeking process of
mosquitoes (Gillies, 1980; Mboera et al. , 1997;
Dekker et al. , 2001; Dekker et al. , 2005; Kline,
2006, 2007; Qiu et al. , 2007a,b; Spitzen et al. ,
2008). Many haematophagous insects are
af ected by CO 2 , including most biting Diptera as
well as Hemiptera such as bed bugs and
triatomines. This cue is known to elicit
behavioural responses in a variety of vectors
and most trap catches are enhanced when it is
used as a lure.
One of the drawbacks of using CO 2 in traps
is that it is logistically dii cult to deploy. For
example, CO 2 cylinders are dii cult to transport
to trapping sites, which are often remote and in
resource-poor countries. Dry ice can be used as
an alternative, but this can be dii cult to source
in some countries and it does not last a long
time, particularly in high temperatures. Also, its
release rate of CO 2 can be highly variable
(Mboera et al. , 1997; Saitoh et al. , 2004). Other
technologies have been developed to produce
CO 2 by burning butane or propane using a
catalytic converter, as with the 'MozzieMagnet',
or by mixing chemicals together to produce CO 2
(Kline, 2002).