Biology Reference
In-Depth Information
the dif erences in habitat preferences. In Brazil, a
15-20-day anaerobic fermentation made of
fresh and mature
Panicum maximum
leaves was
the optimum infusion for trapping ovipositing
St
.
aegypti
and
St
.
albopicta
mosquitoes (Sant'ana
et al
., 2006).
Millar
et al
(1992) isolated and identifi ed
fi ve chemical compounds from a fermented
Bermuda grass infusion, which attracted and
stimulated oviposition of gravid
Cx
.
quin-
quefasciatus
females. The single most attractive
of those compounds was 3-methylindole (or
skatole), not just to
Cx
.
quinquefasciatus
in the
laboratory
(Millar
et al
., 1992) but also to other
species such as
Cx
.
tarsalis
,
Cx
.
stigmatosoma
and
Cx
.
cinereus
in the fi eld (Beehler
et al
., 1994;
Mboera
et al
., 1999, 2000a,b). Odorant
receptors of
Cx
.
quinquefasciatus
are highly
sensitive to skatole and indole (Leal
et al
., 2010;
Pelletier
et al
., 2010). Another plant-derived
compound, which has been isolated from the
summer cypress plant (
Kochia scoparia
) seed oil,
is (Z)-5-hexadecenoic acid, which gets converted
to (5R,6S)-6-acetoxy-5-hexadecanolide (also
known as plant-derived pheromone, PDP)
(Olagbemiro
et al
., 1999). Laboratory and fi eld
assays show that PDP was as ef ective in
stimulating egg-laying of gravid
Cx
.
quinquefasciatus
as a synthetic oviposition
pheromone (Olagbemiro
et al
., 2004). PDP can
be produced at a cost of approximately US$3
g
−1
, US$12 g
−1
cheaper than the conventional
synthetic methods (Logan and Birkett, 2007).
Botanical infusions made from crude plant
extracts have been found to be impossible to
standardize due to variation in fermentation
times, seasonal changes and batch-to-batch
dif erences among plants (Beehler
et al
., 1994;
Mboera
et al
., 1999; Sant'ana
et al
., 2006;
Ponnusamy
et al
., 2010b). Therefore, specifi c
habitat-derived volatiles such as skatole and
PDP, which can be produced commercially, may
be useful tools in future mosquito surveillance
and control programmes.
leaves have an oviposition deterrent and repel-
lent ef ect of 90-100% against
An
.
arabiensis
and
Cx
.
quinquefasciatus
in Sudan (Elimam
et al
.,
2009). The infusion was particularly powerful
when mosquitoes were given a choice between
untreated control and the botanical extract.
When there was no choice, gravid females laid
most of their eggs into cups containing the
lowest extract concentration (Elimam
et al
.,
2009).
Neem tree extracts can inhibit oviposition
in mosquitoes (Mulla and Su, 1999). Gravid
St
.
aegypti
were deterred from egg-laying by crude
neem leaf extract concentrations of 0.005%,
0.05% and 0.5% compared to ethanol, although
egg hatching rates were not af ected (Fuk,
2004). Oral administration of neem extracts
suppressed blood-feeding and oviposition of
Cx
.
tarsalis
and
Cx
.
quinquefasciatus
females (Su and
Mulla, 1999a).
Anopheles stephensi
and
An
.
culicifacies
adult females exposed to neem
volatiles exhibited oviposition suppression and,
after continuous exposure for 7 days, irreversible
inhibition of the gonotrophic cycle (Dhar
et al
.,
1996). Female
An
.
stephensi
treated orally with
the commercial neem formulation NeemAzal
®
(NA), consisting of limonoids, particularly 34%
azadirachtin A, laid fewer eggs (Lucantoni
et al
.,
2006). The number of eggs per microlitre
produced by
An
.
stephensi
decreased from nine
eggs in the control mosquitoes to fi ve eggs at a
concentration of 100 ppm and to zero at a
concentration of 1000 ppm NA. The oviposition
behaviour of
An
.
gambiae
, on the other hand,
was not af ected by crude neem tree extracts in
the laboratory (Howard
et al
., 2011). Overall,
the evidence so far gathered for plant-derived
oviposition repellents is scarce and contradictory.
Before botanical compounds can be used for this
purpose, more practical research is needed.
4.2 Environmental Control of Disease
Vectors with Plants
Many disease vectors rely heavily on key
resources such as suitable aquatic breeding and
larval sites to complete their life cycles. The aim
of environmental control is to modify or
eliminate these aquatic habitats in order to
reduce the number of vectors and disrupt disease
transmission whilst causing minimal adverse
4.1.5 Oviposition repellents
The use of botanical compounds to repel
mosquitoes from potential oviposition sites has
not been extensively explored. Crude aqueous
extracts from castor oil plant
Ricinus communis
![](Biological-and-Environmental-Control-of-Disease-Vectors_images/img-gen68.png)
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