The Use of Plants in Vector Control - Biological and Environmental Control of Disease Vectors - page 54

integrated vector control programmes. For
example, the larvae of Coquilletidia and Mansonia
mosquitoes, vectors of Brugian fi lariasis, are
linked with the presence of several species of
water lettuce (e.g. Pistia , Eichhornia , Salvinia ) as
females attach their eggs on the under-surfaces
of fl oating or emergent leaves (Clements, 1999);
removing this fl oating vegetation as part of the
wider Pondicherry Project resulted in the
disappearance of Brugian fi lariasis in Kerala,
eastern India (Rajagopalan and Das, 1987;
Coosemans and Mouchet, 1990). The clearance
of other aquatic vegetation, such as water
hyacinths and algae, has been demonstrated to
reduce the abundance of the malaria vector An .
subpictus in south-east India (Rajagopalan et al .,
1991). In southern Mexico, Bond et al . (2004)
showed that manual algal removal from
breeding pools signifi cantly reduced larval and
adult densities of An . pseudopunctipennis for up to
6 weeks.

4.2.3 Physical barriers

There are strong data showing that house
modifi cation through physical screening lowers
malaria transmission among users in Africa (see
Kirby, Chapter 7, this volume). While their
uptake is high in urban areas (Ogoma et al .,
2009), the costs for those living in poorer rural
areas may be prohibitive. Another, more cost-
ef ective way of reducing mosquito house entry
for houses in the rural tropics is the use of tall,
densely foliated plants around the houses. This
approach has the advantage that plants are self-
sustaining and cheap to produce. Therefore,
after an initial outlay to produce the plants in a
nursery, a house could be protected continuously
with the only adherence required by
householders being the maintenance of the
plants.
In a recent community study in Tanzania,
Lantana camara L. (lantana) was selected from a
number of plants used by Burundian refugees to
repel mosquitoes and was tested to evaluate its
potential to reduce mosquito house entry
(Mng'ong'o et al ., 2011). There were 56% fewer
An . gambiae s.s., 83% fewer An . funestus s.s. and
50% fewer mosquitoes of any kind in houses
with lantana relative to controls after adjusting
for confounding factors such as house
occupancy and house design. House screening
using lantana reduced indoor densities of
malaria vectors and nuisance mosquitoes with
broad community acceptance. Providing suf-
fi cient plants for one home costs US$1.50
including maintenance and labour costs.
Another controlled fi eld study of lantana was
conducted in Kenya with the same vector species
(Seyoum et al ., 2003). In this trial, ten potted
plants were hung close to the eaves of four
houses over 24 nights; CDC light traps were used
as a proxy for human exposure to host-seeking
mosquitoes. The authors demonstrated a 27.2%
reduction in house entry of An . gambiae s.l.
(mainly An . arabiensis ), about half of the
reduction observed in the Tanzanian study. In
Kenya, there was no repellent ei cacy against
An . funestus contrary to the signifi cant 83%
reduction in Tanzania. The reason for this
dif erence may be related to mosquito density as
the average nightly catch of anophelines in the
Kenya study was more than 300 mosquitoes in

4.2.2 Drainage

The concept of bio-drainage relies on vegetation
to remove excess soil water, and eucalyptus
trees, in addition to being ef ective repellents
(Section 4.1.3), could be utilized as ef ective
water pumps particularly in marshy areas
(Masilamani et al ., 2003). In India, the govern-
ment has supported studies to evolve the best
genotype of eucalyptus with high bio-drainage
ei cacy (Balasubramanian et al ., 2009). As part
of large integrated bio-environmental malaria
control projects, Eucalyptus robusta helped to
drain marshy land and thus reduced vector
breeding sites in Gujarat and Uttar Pradesh in
India (WHO, 1982; Sharma et al ., 1986;
Sharma, 1987, 1991; Sharma and Sharma,
1989). However, it should be noted that the
impact of tree planting on vector abundance
and disease incidence cannot be singled out
or separated from other measures taken as
part of environmental modification program-
mes. None the less, the economic value of
large tree plantations for the local community
should be seen as an important factor
strengthening the idea of the use of such
integrated environmental control schemes
(Sharma, 1987).