Biology Reference
In-Depth Information
may promote a greater spore uptake. Repeated
exposure to fungi may also increase the dose the
insects acquire, resulting in higher mortality
(Blanford
et al.
, 2005). Continuously returning
for blood meals creates multiple opportunities
for exposure of mosquitoes, thus maximizing
coverage.
Mosquitoes also may pick up spores from
other mosquitoes through copulation. Hori-
zontal transfer of fungi between infected and
uninfected mosquitoes has been demonstrated
in three laboratory studies. Copulation of
unexposed male and infected female anophelines
resulted in subsequent infection and reduced
survival of male
An
.
gambiae
s.s. (Scholte
et al.
,
2004b). Male
St
.
aegypti
mosquitoes treated
with
M
.
anisopliae
and
B
.
bassiana
were also able
to transfer spores to untreated females resulting
in 90% mortality within 15 days, reductions in
fecundity of up to 95% and lower female
insemination rates (Garcia-Munguia
et al.
,
2011; Reyes-Villanueva
et al.
, 2011). However,
these studies were carried out in the laboratory
in small cages where the opportunity for close
contact is increased, and further work in semi-
fi eld and fi eld systems is required to see whether
such ef ective horizontal transfer does also occur
in nature.
housefl ies that are implicated with diarrhoeal
disease (Dimbi
et al.
, 2003; Lecuona
et al.
, 2005);
cof ee plants treated with suspensions of
B
.
bassiana
have been investigated for control of
Phlebotomus papatasi
and
Lutzyomia longipalpis
sandfl ies, the primary vectors of leishmaniasis
(Reithinger
et al.
, 1997); nesting boxes to attract
mice (reservoirs for
Borrelia burgdorferi
, the
agent of Lyme disease)
on which
Ixodes scapularis
ticks feed were treated with
M
.
anisopliae
spores
(Hornbostel
et al.
, 2005); boxes baited with
carbon dioxide were treated with
B
.
bassiana
against
Triatoma infestans
bugs, vectors of
Trypanosoma cruzi
(Pedrini
et al.
, 2009).
Using light volatile oils to formulate spores,
walls inside houses can be treated in a similar
way to those during chemical indoor residual
spray programmes (IRS). Applications of
M
.
anisopliae
and
B
.
bassiana
to mud and clay tiles
are ef ective in reducing survival of adult
An
.
gambiae
s.s. and
An
.
stephensi
mosquitoes in the
laboratory. Furthermore, exposure to such
surfaces appears to result in greater mortality
than to treated cloth or cardboard surfaces
(Mnyone
et al.
, 2010; Blanford
et al.
, 2011).
Dark attractive surfaces (Hecht and Hernandez-
Corzo, 1963; Stevenson, 2008) such as black
cotton cloth (Fig. 5.6) acting as resting targets
may be used in place of direct wall treatments
against
St
.
aegypti
(Edman
et al.
, 1997; Paula
et
al.
, 2011). Laboratory experiments have
demonstrated the ef ectiveness of treating black
cloth with spores against anopheline mosquitoes
(Scholte
et al.
, 2005; Stevenson, 2008; Mnyone
et al.
, 2010, 2012; Darbro
et al.
, 2011;
Farenhorst
et al.
, 2011). In experimental huts in
Tanzania,
B
.
bassiana
and
M
.
anisopliae
-treated
netting and black cloth installed in dif erent
ways within the hut were tested for subsequent
infection and survival of
An
.
gambiae
s.l.
mosquitoes (Mnyone
et al.
, 2012) (Fig. 5.7).
Neither treated nets nor cloth curtains around
the eaves were able to infect mosquitoes with
fungi whereas treated cloth bal es installed at
an angle caused almost 70% of mosquitoes to be
infected and reduced survival by as much as
43% compared to controls. This ef ect was
increased by treating strips of black cloth that
were hung around a bed net; 76% of mosquitoes
caught were infected with fungi and survival
was reduced by 45% (Mnyone
et al.
, 2012).
Models demonstrate that such infection rates
Delivery systems tested
The majority of reports on potential uses of
fungi against vectors are based on laboratory
assays, employing either topical application
directly on to the insect (Romana and Fargues,
1992), contact with airborne spores (Clark
et al.
,
1968), sporulating cultures (Rizzo, 1977;
Scholte
et al.
, 2004b) or treated paper surfaces
(Warburg, 1991; Maniania, 1994; Blanford
et
al.
, 2005; Lecuona
et al.
, 2005; Mnyone
et al.
,
2009b). These techniques of infecting insects
were designed mainly as proof-of-principle
experiments and are not transferable for fi eld
use. More recently, traps and devices that could
be employed in the fi eld have been designed.
Pyramidal traps for tsetse fl ies, vectors of
trypanosomes, which cause human sleeping
sickness, were modifi ed to have contaminative
devices containing
M
.
anisopliae
spores
(Maniania
et al.
, 2006); traps with spore-treated
food baits such as rice, maize cobs and molasses
have been used against
Musca domestica
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