The two city corporations, DNCC and DSCC, test mosquito repellents in several stages. However, there have been questions raised over the types of repellents used by city corporation officials.
Specialists say that if a repellent fails to kill 80 percent mosquitoes then it’s deemed ineffective. If 80 percent dies in testing then at the filed level, the actual kill rate is 40 percent.
Before buying mosquito repellents, they are tested. The city corporation sends the medicines to IUDCR and Agriculture Extension Division. Once the reports are satisfactory, they are sent to World Health Organisation (WHO).
Later, the medicine is applied as per the suggestions of WHO. But since the testing system of the city corporations are under question, the repellent is proving to be ineffective at the field level.
City corporation source says that when they buy medicines, they are tested on 50 to 100 mosquitoes locked in a one square feet cage.
Then, the repellent is mixed and fogged from a distance of three feet. After thirty minutes, a check is done to find how many mosquitoes have lost consciousness. A further inspection is done after 24 hours; if 80 percent mosquitoes are dead then the medicine is deemed effective.
On Friday, city corporation tested a repellent from a Bayer Corporation, India. However, in the first thirty minute test, only 18 to 26 percent mosquitoes were found to have lost consciousness.
In the field level, the repellent is sprayed from a distance, so, obviously the question is: if mosquitoes are not neutralized form such a close range of spraying then how can they be killed at the filed level?
After a testing at the city corporation, the repellent is then sent to the Institute of Epidemiology, Disease Control and Research (IEDCR) where a second layer of testing is done. In this testing, Culex mosquitoes are used.
Professor of the Entomology Department Kabirul Bashar adds: “The city corporation needs proper control room to test mosquitoes. They try to use the limited facilities available.”
In the proper scientific system, mosquitoes must be kept in condemn and control rooms and tested 12 times in the former.
Fogging is not effective in dealing with mosquitoes, to properly tackle the issue larvae needs to be destroyed to prevent production of mosquitoes, he opined.