The Use of Plants in Vector Control - Biological and Environmental Control of Disease Vectors - page 51

high vapour pressure, leaving the user
unprotected within 1 h after application (Curtis
et al ., 1987). Mixing citronella with larger
molecules like vanillin can successfully retard
the release rates of the volatile compounds
(Kongkaew et al ., 2011). Recently, nano-
technology has been used to increase the
duration of repellency of citronella by creating
encapsulated nanoemulsions (Nuchuchua et al .,
2009; Sakulku et al ., 2009). Another method of
extending the ef ect of citronella is by
microencapsulation using gelatin-arabic gum,
which prolongs its repellency up to 30 days on
treated fabric stored at 22°C (Specos et al .,
2010). Currently, market products containing
citronella are popular and well accepted, but its
ei cacy against nuisance insects and vectors of
disease falls short of that of other natural
repellent products available (e.g. PMD).
However, given the consumer acceptance and
market shortage of ei cient natural topical
repellents, cosmetic and chemical industries are
increasingly investing in new technologies to
improve natural repellents. Thus, the repellent
market may be revolutionized by a variety of
plant-based repellents, of ering long-lasting
repellency and widening the choice of products
available for consumers.

Bancroftian fi lariasis in the tropics, that
preferentially breeds in polluted waters, is
attracted to fermented infusions from Bermuda
grass ( Cynodon dactylon ) or hay, both in the
laboratory and the fi eld (Isoe et al ., 1995;
Burkett-Cadena and Mullen, 2007; McPhatter
and Debboun, 2009), though this preference
could be altered by a mosquito's larval
environment and prior experience (McCall and
Eaton, 2001). Other botanical infusions
attracting Culex species, such as Cx . nigripalpus
and Cx . erraticus , include oak leaf ( Quercus
virginiana ), algae ( Spirogyra sp.) and acacia leaf
( Acacia schaf neri ) (McPhatter and Debboun,
2009). The tree-hole mosquito Ochlerotatus
triseriatus , a medically important vector of the
La Crosse virus in eastern USA, is attracted to
p -cresol, a component of infusions of decayed
paper birch ( Betula papyrifera ) and other plants
(Bentley et al ., 1979). Stegomyia albopicta and St .
aegypti , which are the principal vectors of
dengue fever, are attracted to infusions made
from senescent bamboo ( Arundinaria gigantea )
and white oak ( Quercus alba ). Overall, St . albopicta
females, which breed in heavily vegetated
waters, are much less specifi c in their oviposition
preferences than gravid St . aegypti mosquitoes,
which are more attracted to infusions made
from low biomass with short fermentation times
(Sant'ana et al ., 2006; Ponnusamy et al .,
2010b). In some studies, St . aegypti mosquitoes
laid more eggs in traps baited with 10% hay
infusions than in tap water (Reiter et al ., 1991;
Chadee et al ., 1993; Polson et al ., 2002), whereas
others found no strong preference (Allan and
Kline, 1995) or a repellent ef ect of Bermuda
hay infusions (Ponnusamy et al ., 2010b). Gravid
St . albopicta females, on the other hand, respond
more strongly and are attracted at hay dilution
concentrations ranging between 10% and 100%
(Allan and Kline, 1995; Ponnusamy et al .,
2010b).
All botanical infusions are dynamic, and
their ef ects on mosquito oviposition depend on
the abundance and diversity of bacterial species,
which is af ected by duration of fermentation,
the plant biomass and the age and species of the
plants used (Ponnusamy et al ., 2010a, b). Isoe et
al . (1995) found that Bermuda grass infusions
fermented for 0-63 days stimulated Cx .
quinquefasciatus , whereas 5-25-day-old in-
fusions were stimulatory to Cx . tarsalis , refl ecting

4.1.4 Oviposition attractants

In many insects, oviposition is governed by
chemical and physical stimuli that lead females
to suitable sites for egg-laying (Bentley and Day,
1989; McCall and Cameron, 1995; Clements,
1999) (see Logan et al ., Chapter 6, this volume).
This behaviour has been exploited in the
development of gravid traps, which include
volatile compounds acting as oviposition site
cues and which attract and then trap ovipositing
females (Polson et al ., 2002; Santos et al ., 2003;
Logan and Birkett, 2007; Obenauer et al ., 2010).
Oviposition attractants have often been made of
infusions from plant materials soaked in water,
which is then used as bait in traps that can then
help to monitor arthropod populations, or even
control them if used in conjunction with
biopesticides, such as Bacillus sphaericus (Mboera
et al ., 2000a).
Culex quinquefasciatus , an important vector
of St Louis encephalitis in the USA and