Biology Reference
In-Depth Information
2
Control with Arthropods
Annabel F.V. Howard*
London School of Hygiene & Tropical Medicine, London, UK
2.1 Introduction
have stable populations that cycle with each
other. For ef ective biological control of disease
vectors, this balance is manipulated, causing
enough disease vector prey to be killed so that
disease transmission is reduced or interrupted
(WHO, 2004). The amount by which vector
populations need to be reduced dif ers between
diseases and their transmission intensities,
making biological control a dynamic process.
Two mechanisms can be employed: (i) release
predator populations into an ecosystem and
encourage their establishment (inoculation); or
(ii) repeatedly release the predators into the
environment (inundation). However, there may
be detrimental ef ects on non-target organisms,
especially if the biological control agent is not
usually found within that ecosystem (Various,
1995). Hence, the World Health Organization
(WHO) recommends only using native
organisms for biological control (WHO, 2002).
Even though the number of reported
predators of disease vectors is high (Jenkins,
1964; Mogi, 2007), there are relatively few
instances where these predators have been used
successfully in control programmes. There are
many reasons for this (Mogi, 2007; Quiroz-
Martinez and Rodriguez-Castro, 2007; Shaalan
and Canyon, 2009), including:
Deploying arthropods to seek and destroy other
arthropods - to some it may sound like science
fi ction, but this is what underpins the whole
concept of biological control. Biological control
is defi ned as the deliberate use of natural
enemies to reduce the number of pest organisms
(Rodriguez-Perez et al ., 2012). While this covers
the whole range of interactions between
predators, parasites and pathogens with their
hosts, it is the predation of arthropods on
arthropods that has been most widely used for
biological control. As early as AD304, the weaver
ant, Oecophylla smaragdina , was being intention-
ally placed into citrus orchards in China to
prevent tree damage by other insects (Tsao and
Li, 1983). Many lessons have been learned since
this early example, but the basic principle has
not greatly changed. Arthropods are still
intentionally being released into the environ-
ment to seek and destroy the target species to be
controlled.
While this is a natural process, there is a
dif erence between natural predation and the
ef ective biological control of disease vectors.
Natural predation is usually balanced within the
ecosystem such that both predator and prey
* afv.howard@gmail.com
 
 
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