Expectant mothers in Calcutta seem to be relatively more susceptible to mosquito bite than others.

A preliminary survey, based on five years? records at 63 malaria clinics of the Calcutta Municipal Corporation (CMC), reveals that the vulnerability of expectant mothers is twice that of non-pregnant women.

According to civic entomologist Debasish Biswas and chief municipal health officer (CMOH) Deb Dwaipayan Chattopadhyay, there may be three reasons for the mosquitoes? preference for pregnant women. First, a woman during pregnancy inhales 20 times more oxygen and, consequently, exhales more carbon dioxide. Mosquitoes are attracted by carbon dioxide.

Second, the rate of sweating is higher in the pre-natal stage, as the woman needs more cooling. The sweat, again, draws mosquitoes.

Third, a pregnant woman needs to relieve herself more often, and for this she has to come out of the mosquito net frequently.

On orders from mayor Bikash Ranjan Bhattacharya and municipal commissioner Alapan Bandyopadhyay, the vector control wing of the civic health department will soon undertake a ?research survey? on mosquitoes in Calcutta. The zoology department of Vidyasagar College will help the civic body in the project. Indranil Kar, a zoology teacher of the college, will lead the research team.

The objective of the survey is to find out the relative concentration of mosquitoes causing diseases like malaria, dengue and filaria in various pockets of the city. The team will also study the insects? nature, biting preference, breeding habit, whether the larvae have developed immunity to select pesticides and whether adult mosquitoes have become immune to repellents.

?The biting preferences of various types of mosquitoes need to be studied thoroughly. For any anti-mosquito drive to be effective, we must know for sure who among men, women and children are the most preferred target of the insect,? CMOH Chattopadhyay said.

Entomologist Biswas said the survey would begin in December. Two most malaria-prone boroughs will be selected for the pilot phase.

?One is likely to be borough VI ? covering New Market, Chandni Chowk, Taltala, Entally, Moulali, Alimuddin Street and Park Circus. The other borough will be in south Calcutta,? he added.

Of the 10-odd species of mosquitoes found in Calcutta, the authorities are concerned over three ? Aedes aegypti (dengue), Culex quinquefasciatus (filaria) and Anopheles stefensi (malaria).

According to records in the civic health department, altogether 3,350 Calcuttans were down with dengue between August 15 and October 31. The death toll has been 11. The malarial toll this year has been four. No patient died of malaria in September-October, though the toll in the same period last year was 14.