The Use of Plants in Vector Control - Biological and Environmental Control of Disease Vectors - page 46

Fig. 4.1. Comparison of 7-day old St . aegypti larvae: bred in (right) 0.05% neem leaf extract and (left)
control (Fok, 2004). (Copyright London School of Hygiene & Tropical Medicine.)

et al ., 2010, 2012). Its application enhances
crop yield and preserves soil fertility and is well
accepted among farmers, therefore showing
promise for incorporation into integrated vector
control programmes of vectors breeding in rice
fi elds. In addition, neem is an environmentally
friendly biopesticide as it is considered non-toxic
to mammals, fi sh and bees (Naumann and
Isman, 1996; Wan et al ., 1996; Raizada et al .,
2001) and causes minimal ecological disruption
through impact on other non-target species
(Schmutterer, 1990).

and central nervous systems of insects. The
insecticide impedes channel closing either by
inactivation or deactivation, and the sodium
channels retain the ability to conduct sodium
ions. However, the membrane potential is shifted
so that the nerve cells function in a new, and
relatively stable, state of abnormal hyper-
excitability. In insects, this produces an in-
capacitating, but sublethal, ef ect known as
'knockdown' (KD). Pyrethrins degrade in
sunlight only a few hours after application,
making them unviable for outdoor use
(Antonious, 2004). However, they leave very
little residue and have low mammalian toxicity,
making them ideal insecticides for indoor
fumigation. They are commonly found in
household insect sprays used in combination
with piperonyl-butoxide (PBO), a non-
insecticidal synergist, to kill housefl ies, cock-
roaches and mosquitoes.
Structural modifi cation of pyrethrins
during the period between 1924 and 1970
produced the fi rst synthetic pyrethroids, the
most successful of which was allethrin, which
closely duplicated the structure of cinerin I and
is still commonly used today in mosquito coils.
Photostable compounds, with high insecticidal

4.1.2 Adulticides

Pyrethrum
Pyrethrum is a botanical biopesticide used since
400 BC to kill insects in Persia, where children
were deloused using a powder obtained from
the dried fl owers of the plant Tanacetum
cinerariaefolium . Its insecticidal properties are
attributable to the presence of pyrethrin I and II,
jasmolin I and II, and cinerin I and II (Davies et
al ., 2007), which are neurotoxic substances that
modify the sodium gated channels of peripheral