Biological Control of Mosquitoes
Read about the biological control of mosquitoes. With the increasing menace of mosquitoes and resulting spread of different epidemics, pesticides are widely used everywhere. Pesticides are harmful to the environment. As an alternative, biological method where in certain species of fishes,feeding on the mosquito larvae, are grown in waters.
Problem of pests
There are different pests in nature which are either friends or foes to human beings. Man has developed means to destroy these pests, especially which are foes, by artificial methods. With the development of Chemistry man could work out the effects of various combinations of materials collected from nature. He found out the lethal effects of some of these combinations when applied on pests. Thus different pesticides were developed which could control various pests which were foes to man. These were developed mainly for the agricultural purposes where the production got reduced due to the attack of pests. To a large extent these pesticides were found to be useful in controlling the pests. However, these pesticides could not identify the pests whether they were friends or foes, which lead to environmental problems. Mosquitoes and related issues
Mosquitoes also came into the list of pests of man when he recognised its role in spreading certain diseases such as filaria, malaria, etc. Naturally, man wanted to control the growth of mosquito population. The pesticides developed for other pests were used against them. Results were positive in the case of certain pesticides. This lead to the wide use of them against mosquitoes. No consideration was given to the environmental impact of this, which lead to protests from all corners.Biological method for mosquito control
Search for alternative methods of mosquito control began in different parts of the world. Nature showed the way. Mosquitoes lay their eggs in stable waters and larvae grow out of them. On observation it was seen that certain varieties of fish eat these larvae. This lead to finding out the species of fish eating on fish larvae. Guppies (Precilia retticulata) and Gambucia (Gambucia affinis) species were identified. So growing these species of fishes could control the production of mosquitoes, this information was passed far and wide. This showed positive results to certain extent. Thus the biological method was adapted as an alternative method.Shortcomings of the method
But some of the recent studies showed that this method was not giving the expected results in the long run always. The attempt to control mosquitoes causing spread of malaria in America by growing guppies in water sources did not result in success. The guppies released in waters were feeding on mosquito larvae, but not of those mosquitoes causing malaria spread. More over these guppies were eating other small life forms including zoo-plankton. This caused other environmental problems in the water bodies.
Certain studies from India report that this biological control of mosquitoes are showing positive results. However, the reliability of these studies are questioned, mainly because simultaneous use of high quantity of pesticides to eradicate mosquitoes. Another drawback of these studies were that it concentrated on the number of persons affected by such diseases spread through mosquitoes. This approach could not reason out whether the reduction in the number of affected persons is due to people's awareness about the disease or due to reduction of mosquito population through biological means.
As pointed out when the population of these mosquito larvae eating fishes increase they start eating other live organisms present there, especially the zoo-plankton which are preferred by these species of fishes. This results in the increase of phytoplankton population causing oxygen depletion in the water body. If the oxygen level comes down the life in the water body become impossible and the living organisms including fishes start dieing.Search continues
Guppies and gambucia have a tendency to eat small live organisms, which include back swimmers and small water beetles. Reduction of their number indirectly help increase the mosquito population in future, since these beetles also feed on mosquitoes. Reduction in zoo-plankton the food availability for other varieties of fishes, especially for the small varieties. When the number of small varieties reduce, it will affect the larger varieties also since they depend on small ones for their food. Thus the growing of guppies and gambucia lead to different environmental problems in the water body.
The above issues have again compelled to go for other species of fishes. Locally available fishes which feed on mosquitoes are a suggested alternative. They are already living in the local ecosystem and is part of the life system there. Hence allowing to multiply the number of those fishes which prey on mosquito larvae will not be a harm to the environment.Kerala's choice
In Kerala the larvae eating Anabas testudiencis can be one of the choices. This species has the capacity to survive and multiply in waters which are highly contaminated and with depleted oxygen level. It takes oxygen from the atmosphere also. This species of fish consume more larvae at a time compared to guppies and gambucia. Anabas takes between 980 to 1300 larvae at a time while guppies take only in between 40 to 175 larvae. Also Anabas prefer mosquito larvae than other small living organisms. Another advantage is that the population of Anabas can be controlled since it is an edible fish. These fishes are available in almost all water bodies in Kerala, though not in markets.
Job oriented