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and exposes spores on the material surface
(Farenhorst and Knols, 2010).
Formulation of spores may also overcome
repellency. Scholte (2004) demonstrated that
conidia of M . anisopliae have a repellent ef ect on
An . gambiae , with 81% of mosquitoes escaping
from a cylinder containing a Petri dish of 5 g of
dry conidia to a chamber without conidia
compared to 11% exiting a cylinder with an
empty dish. However, this repellent ef ect was
reduced when conidia were formulated in oil
and applied to fi lter paper. Similarly, no evidence
of repellency was observed when mosquitoes
were placed in a choice chamber fi tted with
netting treated with oil-formulations of M .
anisopliae and B . bassiana at a variety of dosages
(Mnyone et al. , 2010). However, the formulation
chosen must also be carefully considered.
Certain pure oils can repel insects, for example
pure maize, thistle and linseed oils repel Triatoma
infestans bugs (Luz and Batagin, 2005). More
examples of essential oils that repel mosquitoes
are described elsewhere (Lorenz et al ., Chapter 4,
this volume).
than those mosquitoes that were exposed up to
36 h after blood-feeding, with susceptibility
resuming to pre-blood-fed levels 72 h after
taking a blood meal (Mnyone et al ., 2011). Other
studies of An . stephensi females showed that,
after 14 days, more mosquitoes survived fungal
exposure to B . bassiana if they had blood fed than
those that were solely sugar fed (Stevenson,
2008). However, here, blood-fed mosquitoes
generally survived longer and the impact of
fungal infection became evident later in life. The
proportional reduction in survival over the
lifetime of the mosquito due to fungal infection
was similar between blood-fed and non-blood-
fed mosquitoes (Stevenson, 2008).
These fi ndings have important implications
for how fungi should be applied in the fi eld. To
encourage extended resting of mosquitoes long
enough to pick up a sui cient number of spores,
targeting mosquitoes after blood feeding would
appear the most ef ective method. However, for a
faster kill and an increased likelihood of
mortality before the next blood meal (and
potentially
transmission),
targeting
unfed
mosquitoes may be more appropriate.
Gonotrophic state
Depending on where and how fungi are
deployed, adult mosquitoes may be targeted at
dif erent stages in their gonotrophic cycle.
Females may be unfed, may have fed solely on
sugars, may have taken a blood meal or may be
semi-gravid or gravid. Nutrition can greatly
infl uence the outcome of an infection. There are
reports of repeated blood-feeding increasing
mosquito Plasmodium infections (Terzian et al. ,
1956; Okech et al. , 2004) but blood ingestion
has also been associated with elevated immune
responses (Gass, 1977; Chun et al. , 1995; Koella
and Sørensen, 2002).
Studies on fungal-exposed mosquitoes that
examine comparative infection levels and
mortality of blood-fed and sugar-fed mosquitoes
have demonstrated varying results. Stegomyia
aegypti females were less susceptible to M .
anisopliae immediately after blood-feeding than
their sugar-fed counterparts, but their sus-
ceptibility returned to pre-blood-feeding levels
after the blood meal digestion (Paula et al .,
2011). Similarly, sugar-fed An . gambiae s.s.
mosquitoes exposed to B . bassiana and M .
anisopliae were more susceptible to infection
Behaviour of mosquitoes
In designing delivery systems the behaviours of
the target species must be known. Some
mosquitoes display endophagic and endophilic
behaviours (Russell et al. , 2011), whereas others
may be purely indoor resting and feeding.
Mosquitoes also show dif erent behaviours at
dif erent stages of their gonotrophic cycle. Host-
seeking mosquitoes may briefl y brush past
surfaces of curtains or nets (Farenhorst et al. ,
2011), and after blood-feeding may rest for
extended periods of time on a surface. Laboratory
experiments have shown that the longer the
exposure to fungal treated surfaces, the quicker
the kill, with this trend more evident for lower
spore concentrations (Stevenson, 2008).
Laboratory experiments with adult An . gambiae
s.s. demonstrate that sui ciently high mortality
levels can result after exposure times of 30 min
with appropriate spore concentrations (Mnyone
et al. , 2009a; Farenhorst et al. , 2011).
Anophelines have also been shown to actively
seek out and rest longer on dark surfaces
(Stevenson, 2008), therefore dark-coloured
targets or surfaces that encourage longer resting
 
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