Vector Control Using Semiochemicals - Biological and Environmental Control of Disease Vectors - page 103

Although a lure-and-kill approach looks
promising for Stegomyia , before wide-scale use,
the implications of skip oviposition should be
considered. It has been proposed that Stegomyia
mosquitoes, unlike Culex , practise a behaviour
known as skip oviposition where a single female
will lay a few eggs in one site but withhold the
remaining eggs for deposition in several dif erent
sites (Colton et al. , 2003). However, such
evidence has been contested (Harrington and
Edman, 2001). Should skip oviposition be
common practice, it has been suggested, from
laboratory studies where St. aegypti did not
withhold any eggs when no site choice was
available (regardless on the density of conspecifi c
eggs present), that there is a hierarchy of events
determining oviposition site selection and
semiochemicals from eggs may not be suitable
for surveillance (Williams et al. , 2008).
In laboratory studies, it was shown that
bacteria present in breeding water elicited
greater oviposition attractancy for St. aegypti
and St. albopicta than conspecifi c eggs (Pavlovich
and Rockett, 2000). In a fi eld trial, St. aegypti ,
unlike Cx. quinquefasciatus females, laid more
eggs in a fungal infusion than in a control
(Sivagnaname et al. , 2001). The authors con-
cluded that there was scope for developing a trap
incorporating the fungal infusion with an IGR
for surveillance and/or control of St. aegypti
(Sivagnaname et al. , 2001). However, grass
infusions are more typically used for trapping
and, in Brazil, the optimum infusion to be used
with ovitraps for Stegomyia surveillance was
made from 15- or 20-day-old anaerobic ferment-
ation of fresh, fully mature leaves of Panicum
maximum (Sant'ana et al. , 2006).
To screen potential oviposition attractants
using a suitable trapping method that quantify
the number of eggs laid, sticky ovitraps are
favoured over standard ovitraps, because they
capture Stegomyia mosquitoes that are attracted
to an organic infusion before they may or may
not also be stimulated to lay eggs (Ritchie et al. ,
2003; Trexler et al. , 2003; Zhang and Lei,
2008). The use of sticky ovitraps, to confi rm
electrophysiological studies, showed that fi ve
potential volatile synthetic chemicals (dimethyl
disulfi de, indole, 4-methylphenol, 3-methylindole
and trimethylamine) were not oviposition
attractants, and therefore inef ective lures for
baiting ovitraps for surveillance or control of St.

albopicta (Trexler et al. , 2003). As discussed
in the section above, a more recent approach to
identify and screen candidate compounds is
to study OBPs, and this approach was used to
develop the infusion-based lure TMA that is
currently used in gravid trapping in Brazil (Leal
et al. , 2008). Synthetic lures, such as AtrAedes,
are commonly used with a sticky MosquiTRAP
(Braga and Valle, 2007; Eiras and Resende,
2009). However, although MosquiTRAPs
captured a higher mean number of female St.
aegypti per trap than Adultraps, a disadvantage
is that, if not regularly maintained, they could
serve as potential oviposition sites for female
mosquitoes (Maciel-de-Freitas et al. , 2008).
Interestingly, for the purposes of integrated
vector management, gravid St. aegypti females
were signifi cantly more attracted to ovitraps
containing the predacious copepod Mesocyclops
longisetus , or to ovitraps with water in which
copepods were held previously, than to distilled
water, possibly due to monoterpene and sesquiter-
pene compounds such as 3-carene, -terpinene,
-copaene, -longipinene, -cedrene and
-cadinene (Torres-Estrada et al. , 2001). Similarly,
gravid St. notoscriptus oviposited more eggs in
water that had contained larvivorous Mela-
notaenia duboulayi fi sh (one fi sh in 5 l of water),
but the potential kairomone eliciting the response
was not identifi ed (Hurst et al. , 2010).
Kairomones that have been identifi ed as
oviposition stimulants for St. aegypti include
specifi c bacteria-associated carboxylic acids and
methyl esters (Ponnusamy et al. , 2008). For
example, more eggs were laid by St. aegypti in
traps baited with a synthetic mixture of 83%
tetradecanoic acid, 16% nonanoic acid and 1%
tetradecanoic acid methyl ester, at a dose of 0.6
ng NTT μl −1 (fi nal concentration in trap,
approximate to 0.033 ng ml −1 ) (Barbosa et al. ,
2010a). A series of aryl hydrazono esters, at a
concentration of 10 μg ml −1 , elicited an
oviposition activity index (OAI) of +0.299
(greater than 95% confi dence limit) in dual
choice tests, using St. albopicta mosquitoes,
similar to that obtained for p-cresol (OAI
+0.320), an established oviposition attractant
for St. aegypti (Bandyopadhyay et al. , 2011).
An alternative approach is to use
kairomones that elicit oviposition repellency.
Waters containing conspecifi c larvae of St.
aegypti parasitized by the digenean fl atworm