Biology Reference
In-Depth Information
and Walton, 2008). In Brazil, Betta splendens fi sh
decreased the number of eggs laid by St . aegypti
females from 186.5 per week in the control
group to 32.5 per week when the fi sh were
present (de Goés Cavalcanti Pamplona et al .,
2009).
move occasionally to the surface water for their
respiration, it is desirable to choose larvivorous
fi sh that are surface feeders and carnivorous.
Suitable fi sh should have a preference for
mosquito larvae and pupae over other food, but
still be able to maintain high population densities
on diverse nutritional sources when few
immature stages are available (i.e. when nearing
mosquito population elimination stage). Lar-
vivorous fi sh should also have high search
ei ciency and attack rates and low handling
time. They should have equal food consumption
rates at day and night, and detect food sources
by mechano-reception as well as with normal
visual ability. They should also ideally have no
food value, so that fi sh-eating people discard
them and the fi sh can maintain high population
densities throughout the year. It is dii cult or
almost impossible to fi nd a fi sh species that
satisfi es all of the above parameters. Hence, the
choice usually depends upon those which satisfy
as many of the desirable qualities as possible.
Prior to introduction as biological control
agents, the fi sh's adaptability to novel
environments and ecological interactions with
indigenous organisms need to be considered
(Denoth et al ., 2002; Carlson et al ., 2004). Thus,
before recommending any larvivorous fi sh,
whether indigenous or introduced, in mosquito
control operations, it is important to have a
sound general knowledge of a predator's
selective prey patterns, and particularly of its
mosquito larval selection in the presence of
alternative natural prey (Arthington and Lloyd,
1989; Arthington and Marshall, 1999). For
example, in Kolkata, India, the feeding
preferences of guppies ( Poecilia reticulata ) were
assessed, and it was found that chironomid
larvae and tubifi cid worms were favoured over
Cx . quinquefasciatus larvae (Manna et al ., 2008).
Thus, the next step includes the study of
mosquito control ei cacy of the particular
larvivorous fi sh in laboratory bioassays. In the
laboratory, the predatory ei cacy can be
determined in short term and long term assays,
including the rate of larval consumption (daily
feeding rate) under certain laboratory conditions
as well as in combination with variable
environmental parameters such as light,
temperature, pollution level, presence/absence
of aquatic vegetation, pH and humidity. The rate
of optimal foraging, niche and food breadth, and
3.5 Recommendations and Future
Strategies
Taking into consideration the negative impacts
of the application of Gambusia or other exotic
fi sh in mosquito control operations, the use of
the native indigenous fi shes can be suitable in
certain situations. Studies from Argentina have
shown that the indigenous fi sh Cnesterodom
decemmaculatus and Jenynsia multidentata can
regulate mosquito populations in ditches (Marti
et al ., 2006). In Mexico, the indigenous fi sh
Lepisosteus tropicus , Astyanax fasciatus , Brycon
guatemalensis , Ictalurus meridionalis and Poecilia
sphenops have been employed in regulating
mosquito immature stages (Martinez-Ibarra et
al ., 2002). In Australian salt marshes, Pseudo-
mugil signifer has been recorded as a potential
predator of mosquito larvae (Morton et al .,
1988).
The application of larvivorous fi sh as an
integrated option of biocontrol operations could
be fruitful if a systematic approach is under-
taken. The initial step for the introduction of
larvivorous fi sh in mosquito control would be
the selection of suitable species. By modelling
the dynamics between host-vector interactions
(such as humans and mosquitoes) and predator-
prey (such as fi sh and mosquitoes) relationships,
the potential impacts of larvivorous fi sh on
malaria transmission can be evaluated and
particular traits of ef ective control agents can
be highlighted (Lou and Zhao, 2011).
Larvivorous fi sh that are small in size are more
compatible because they can move easily in
shallow water and among thick vegetation in
mosquitogenic sites (Job, 1940). They should be
'hardy' so they can survive and breed in the
adverse physico-chemical conditions of fresh
and brackish waters and so they can be
transported to remote fi eld sites. They must
breed freely and successfully in confi ned waters
such as temporary pools and embankments, and
may be drought resistant. As mosquito larvae
 
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