Control with Arthropods - Biological and Environmental Control of Disease Vectors - page 17

than 90% reduction in St . aegypti numbers
following the release of Tx . splendens larvae into
water tanks in Bangkok (Wongsiri and Andre,
1984). In the Caribbean, a trial highlighted the
ef ects of Tx . moctezuma 1 month after their
release. The proportion of containers with St .
aegypti larvae was signifi cantly smaller in the
treatment village, but remained the same in the
control village, compared to baseline levels.
There was also a signifi cant decrease in the
number of adult Stegomyia collected; 80% fewer
St . aegypti females were caught in the Tx .
moctezuma -treated village when compared to
pre-treatment levels. However, the released
predator was unable to establish itself on the
island (Rawlins et al ., 1991). Similarly, a study in
St Maarten in the Caribbean introduced Tx .
brevipalpis eggs into all identifi ed St . aegypti-
positive larval habitats and found that within 16
days, no more St . aegypti larvae could be found
within the treated habitats. However, as Tx .
brevipalpis did not establish itself on the island
and St . aegypti mosquitoes soon returned to pre-
intervention levels, repeat treatments would be
required every 4 weeks for successful dengue
control (Gerberg and Visser, 1978).
In general, establishment of the biological
control tool is preferable because it leads to
sustainable disease vector control, which can be
more cost-ef ective. However, most of the studies
looking at the ef ectiveness of Toxorhynchites
species for Stegomyia control have used
inundative releases, mainly because Toxo-
rhynchites do not establish populations well in
new environments. Continuous releases of
Toxorhynchites can make vector control labour
intensive and expensive, and will not work if the
predator and prey oviposition sites are
completely unrelated. In addition, laboratory
rearing of Toxorhynchites can be dii cult due to
the need for live food and the precautions that
need to be taken to avoid cannibalism (Focks,
2007). In addition, intensive and frequent
releases of Toxorhynchites do not necessarily lead
to ef ective vector control. In Java (Indonesia),
for example, Tx . amboinensis larvae were
introduced to Stegomyia larval habitats bi-
weekly for 7 months, but there were no
signifi cant dif erences in number of dengue
vectors between the treatment and control areas
(Annis et al ., 1990). Thus, in some areas, the use
of Toxorhynchites would be more ef ective when

incorporated into an IVM strategy (Schreiber,
2007).
While Toxorhynchites mosquitoes have been
used to control Stegomyia mosquitoes in the fi eld
for several decades, there have been no studies
looking for a link between the use of
Toxorhynchites and a reduction in dengue disease
dynamics. In addition, unlike for copepods,
Toxorhynchites have not been oi cially adopted
as part of a national disease control programme.
Nevertheless, there is potential for the use of
Toxorhynchites to help control dengue vectors as
part of an IVM strategy. Guidelines exist
specifi cally relating to Toxorhynchites rearing
methods for biological control (Focks, 2007).
Before their wide-scale use, the production costs
will have to decrease, but there is potential for
af ordable production in some institutions in
some countries, leading to a promising biological
control tool that can be used to greater ef ect in
the future.

2.3 Malaria and Lymphatic Filariasis
Control

Malaria and lymphatic fi lariasis are diseases also
transmitted by mosquitoes. Malaria is a parasitic
disease that is predictable (Zhou et al ., 2004),
preventable (Chanda et al ., 2008) and treatable
(Barnes et al ., 2009). Despite this, vast numbers
of people are being killed by malaria annually,
with estimates for 2010 ranging from 655,000
(WHO, 2011) to 1,240,000 (Murray et al .,
2012) deaths. Malaria is transmitted to humans
by female mosquitoes in the Anopheles genus
taking blood meals. Larval control for Anopheles
is used less than for Stegomyia control for two
reasons. First, targeting adult Anopheles
mosquitoes is more ef ective than Stegomyia as
Anopheles are nocturnally active and attracted
by sleeping humans; therefore, the use of
insecticide-treated products, such as bed nets,
has been the mainstay of malaria vector control
for decades. Second, the larval habitats of
Anopheles are less well defi ned, more rural than
peri-domestic, and therefore not as easy to locate
and treat as Stegomyia habitats.
Culex mosquitoes transmit a range of
debilitating diseases, including Bancroftian
lymphatic fi lariasis, Japanese encephalitis and
West Nile virus. Culex females also take blood