80. Prospects for Bioethical
Management of Mosquito menace and Mosquito-borne Diseases
Department of Zoology, Loyola College, Chennai 600 034
While World Health Organization has become
successful in eradicating Variola virus in the world and becoming
successful in controlling Polio virus by the year 2000 (WHO, 1996),
the tiny insect - mosquito - challenges WHO in its existence due
to environmental degradation and loss of bioethical values.
Mosquito is primarily a nuisance in human dwellings that makes him restless and psychic. It bothers us in various means affecting concentration on work and sleep comfort. More than this, it is known to be the vector for many dreadful diseases namely malaria, filariasis, Japanese encephalitis (JE), dengue fever etc. All such diseases thrust on us a great burden and risk in our economical, social, cultural and moral values.
Loss of physical health makes us susceptible
for secondary infection such as common cold and diarrhea. This
results in mental agony leading to internal conflicts, loss of
self control and depression. These disturbances affect us badly
in the social dimensions. The quantity and quality of an individual's
interpersonalities and the extent of involvement with the community
While controlling mosquitoes, people have
totally ignored bioethical values including the ecobalance of
his environment. These approaches are multifaceted but most of
them are hazardous:
I. Insecticides: The intensive and
extensive spray of insecticide in the human dwelling in controlling
adult mosquitoes cause emphysematic problems such as bronchitis,
asthma and such other respiratory ailments.
ii. Repellants: Of course, repellants
keep away mosquitoes from his surroundings. But it causes tremendous
economic setback, respiratory congestion and unethical industrial
development. Above all, this method is purely a momentary relief
than a permanent remedy to him.
iii. Resistance to insecticide:
Development of resistance by mosquitoes against such insecticides
provides more impact in producing highly toxic chemicals, over
a period of time that can be listed as organochlorine (DDT, BHC,
aldrin), organophosphate (malathion, parathion and fenitrothion),
carbonates (Carbofuran) and pyrethroids (Decamethrin).
iv. Non-target forms: The inability
of pesticide to discriminate pests and non pests in the field
also affect the beneficial forms such as fishes and amphibians
in the mosquito breeding sites.
v. Bio-concentration: Another problem
with pesticides is that of bio concentration and biomagnification.
An ideal pesticide that is non persistent, non-toxic, biodegradable
with a complete control of only the target pest namely mosquito
in the deteriorating environment is beyond our dreams.
Hence awareness of the general health
problems, willingness to help others and serious civic sense are
essential. But the demographic pressure on all sorts of natural
resources continuously went on increasing to the present modern
age of science and technology. Evolutionarily speaking, deforestation,
indiscriminate use of pesticide and depletion of ecosystem resulted
in the loss of biodiversity.
Natural selection never failed in an ecosystem
to check the alarming growth and propagation of a particular plant
and animal species but for human interference with his technological
advancement. It is the high time that man utilizes the natural
enemies of mosquitoes such as predators and parasites as biocontrol
Among many biocides, use of Bacillus
thuringiensis israelensis and Bacillus sphaericus in
controlling mosquitoes in fresh water media is recommended, since
they parasitise them during destruction. Gambusia has been
recommended as a predator on larval mosquitoes in fresh water
bodies such as domestic wells. The limiting factor is its state
of satiation being attained in a short duration. Another voracious
predator is water bugs.
Among water bugs, members of Diplonychus indicus belonging to sub order Heteroptera of class Insecta are not only voracious predators, but also kill the mosquito larvae and partly suck their contents with their rostrum so that satiation time is delayed (Fig 1 and 2).
Some reasons for the suitability of the aquatic bug as biogent follow :
1. It is a highly efficient predator both on anopheline and culicine larvae;
2. en masse rearing is possible due to size;
3. All immature stages and adults kill mosquito larvae;
4. Sexual dimorphism is distinct morphologically that facilitates sorting;
5. Males carry the eggs on their backs;
6. Increased predation is distinct in male;
7. Cannibalistic behaviour occurs during overcrowding so that the bug's population size is self controlled and
8. The male showed preferential selection
for the large rather than small sized prey (Venkatesan et al.,
1986; Venkatesan and D'sylva ,1990).
Success In Biocontrol
It is an economic decision Coevolution
and balance in predator and prey system should not be negatively
looked upon. If the equilibrium achieved between them results
in a relatively low mosquito population then an effective, economic
control is possible and bio control is successful.
Though many such biocontrol agents are known, the natural voracious predator of mosquito larvae has been recognised as the water bugs in general and the belostomatid bug in particular which has many beneficial characters.
Hence it is more ethical in the benefits of "new association" approach of Pimental (1988) with a tendency to have a relatively balanced economy. This may be thought of while using water bugs in mosquito breeding system.
Such a bioethical approach to tackle the
situation with a biosense will certainly be a suitable and effective
alternative to insecticides so that obsolete and environmentally
harmful technologies that are being total failure are not passed
on through many years making the mosquito a menace beyond management.
Pimental, D. 1988 Improved success in biological control. Bicovas, proceedings 1:90-92.
Venkatesan, P., Cornelissen, G. and Halberg, F. 1986 Modelling prey predator cycle using hemipteran predators of mosquito larvae for reducing world wide mosquito borne disease incidence. Chronobiol. 13 (4) : 351 - 354.
Venkatesan, P. and Tena D'sylva,
1990. Influence of prey size on choice by the water bug - Diplonychus
indicus Venk & Rao (Hemiptera; Belostomatidae) J.Ent.Res.
14(2) : 130 - 138.
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