Vector Control Using Semiochemicals - Biological and Environmental Control of Disease Vectors - page 104

Plagiorchis elegans contained signifi cantly fewer
eggs than waters containing unparasitized
larvae. Thus, the authors proposed that gravid
St. aegypti were deterred from ovipositing in
response to a chemical found in waters con-
taining parasitized larvae (Lowenberger and
Rau, 1994). Although the biologically active
chemicals were not identifi ed, in subsequent
studies, some C(21) fatty acid esters, hexadecyl
pentanoate, tetradecyl heptanoate and tridecyl
octanoate, elicited signifi cant oviposition
repellent activity against St. aegypti and St.
albopicta in the laboratory (Sharma et al. , 2008),
and hexadecyl pentanoate loaded on to an
ef ervescent tablet retained its repellent property
against both species in treated fi eld sites for up to
1 week at 10 mg l −1 (Seenivasagan et al. , 2010).
The authors discussed the possible utilization of
these esters in integrated vector management
(Sharma et al. , 2008; Seenivasagan et al. , 2010).

domain, work on identifying semiochemicals for
Anopheles monitoring and control is ongoing.

Simulium blackfl ies
The fi rst laboratory observation that gravid
females belonging to the Simulium damnosum
complex preferentially oviposit at sites
containing freshly laid conspecifi c eggs was
made by McCall et al. (1994). Using air
entrainment and GC analysis, two volatiles were
collected emanating from eggs deposited less
than 12 h previously, and in two choice
bioassays, they were shown to be behaviourally
active in wild-caught gravid S. damnosum from
Sierra Leone (McCall, 1995). The two
compounds also elicited a response in gravid
females of S. yahense from Ghana (McCall et al. ,
1997a), and were present in hexane extracts of
gravid ovaries, 2 days post-blood meal, from six
species or forms belonging to the S. damnosum
complex: S. leonense (Sierra Leone), S. yahense
(Ghana), S. sanctipauli (Ghana), S. squamosum
(Cameroon), S. sirbanum (Ghana) and the Bioko
form (island of Bioko, Equatorial Guinea)
(McCall et al. , 1997b). As the same pheromone
was common throughout the species complex
that transmits onchocerciasis across large areas
of Africa, the authors suggested the possibility
of developing an odour-baited trapping system
for blackfl ies (McCall et al. , 1997b). Communal
oviposition was also observed in bioassays using
a Neotropical blackfl y vector, S. ochraceum , in
response to conspecifi c eggs, but further
experimentation, using extracts of eggs, is
required to confi rm that the response is
chemically-mediated (Rodriguez-Perez et al. ,
2003). Large elimination programmes, such as
the WHO African Programme for Onchocerciasis
Control, using ivermectin for clinical impact,
and aerial and ground-based applications of the
larvicide temephos to all watercourses with fast-
fl owing water to interrupt transmission (Traore
et al. , 2009), have achieved their goal of
sustained elimination, making the need for
incorporating odour-baited traps in integrated
programmes redundant. However, oviposition
pheromones may be used to improve the
maintenance of laboratory colonies of Simulium
species that are dii cult to rear through
successive generations (Wilson et al. , 2000). For
example, single gravid S. sanctipaoli s.s. were

Anopheles mosquitoes
Compared with culicine mosquitoes, less
attention has been paid to the possible exploit-
ation of oviposition behaviour of anophelines.
Instead, research groups have placed a greater
emphasis on the possible role of host-seeking
kairomones (see Section 6.2.1). Nevertheless,
there has been a recent growing interest in
understanding the behaviour of anopheline
mosquitoes since it was demonstrated that
An. gambiae mosquitoes preferred to oviposit in
water containing semiochemicals produced by
live microorganisms (Sumba et al. , 2004).
Further more, conspecifi c larvae (Ogbunugafor
and Sumba, 2008), but not conspecifi c eggs
(Sumba et al. , 2008), elicited a similar response in
Kenyan An. gambiae s.s. The response varied
depending on the quality of breeding water and
the density of larvae used; high densities of larvae
deterred oviposition (Sumba et al. , 2008). Further
work has focused on the screening of potential
oviposition attractants from bacterial isolates and
13 putative compounds have been identifi ed for
An. gambiae mosquitoes (Lindh et al. , 2008).
Another study showed that the fatty acid esters
nonyl-dodecanoate, decyl-undecanoate, propyl-
octadecanoate, and pentyl-hexadecanoate
induced concentration-dependent positive ovi-
position responses in An. stephensi mosquitoes
(Sharma et al. , 2009). Although not in the public