Ananya Dutta

To control the mosquito menace in the eastern metropolis

Toxorhynchitis larvae feed on larvae of other mosquitoes including those that transmit diseases

Unlike most mosquitoes, the adult form of Toxorhynchitis does not bite humans

KOLKATA: The big fish eat the small is a universal law of nature and researchers of the Kolkata Municipal Corporation’s (KMC) Vector Control Laboratory are now applying it to control the mosquito menace by setting “giant cannibalistic” ones on the trail of those that cause diseases.

Larvae of the Toxorhynchitis genus, which comprises of about 60 species, feed on larvae of other mosquitoes including those that transmit diseases like malaria, dengue, chikungunya and encephalitis, Dr. Debashis Biswas, senior vector control officer and chief entomologist of KMC told The Hindu here on Friday.

In the course of a routine larval surveillance, Dr. Bhitika Mondal, a consultative entomologist to KMC’s vector Control Office chanced upon a larva of the Toxorhynchitis splendence mosquito, said Dr. Biswas.

Effective check

“Unlike most mosquitoes, the adult form of Toxorhynchitis does not bite humans, so we are looking into the possibility of using it for vector control,” he added.

Since the larval stage of this variety is up to 25 days as compared to the three to four days of ordinary mosquitoes, it can be an effective way of keeping a check on the vector population.

However, researchers are still grappling with the problem of multiplying these mosquitoes in the laboratory as very little is known about the conditions they breed in, he said.

Question marks

A biological means to control mosquito breeding is significant for a country like India which reported nearly 1,700 deaths in 2008 caused by diseases spread by mosquitoes, but experts are sceptical of its success.

“The use of Toxorhynchitis has shown limited success in controlling the population of dengue causing mosquitoes when used along with an adulticide,” a senior entomologist of the Armed Forces Medical College told The Hindu.

But, it has very little chance of success in controlling other mosquitoes. Toxorhynchitis larvae are found in natural or artificial containers like rock-pools or tree holes whereas mosquitoes like malaria causing anopheles breed in large open ponds, she said.

Breeding of the mosquitoes will also pose a problem as being cannibalistic by nature, they devour not only larvae of other mosquitoes, but also of their own kind, which means only one larva can be kept in one breeding tank, she added.