Bioethics in India: Proceedings of the International Bioethics Workshop in Madras: Biomanagement of Biogeoresources, 16-19 Jan. 1997, University of Madras; Editors: Jayapaul Azariah, Hilda Azariah, & Darryl R.J. Macer, Copyright Eubios Ethics Institute 1997.
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80. Prospects for Bioethical Management of Mosquito menace and Mosquito-borne Diseases

P. Venkatesan

Department of Zoology, Loyola College, Chennai 600 034


The tiny insect, very highly adaptable to living methods of humans in the world and in India in particular, is the mosquito that challenges humankind in its widespread occurrence and causation of dreadful diseases to man. The management of mosquito with insecticidal spray ends in deleterious side effect through biomagnification. Use of repellents in human dwellings results in psychic, neurotic and health hazards to humans including bronchitis and allergic asthma. Use of biocides and its application in ethical way as an alternative - is discussed.

Introduction

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.

Vector

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 is lost.

Human Approach

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

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 agents.

Biocides

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.

Diplonychus indicus

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.

Conclusion

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.

References

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.


Please send comments to Email < Macer@biol.tsukuba.ac.jp >.

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