Mosquito free airport perimeter:

Ref: 21st edition Park, pg 259Explanation:India is a yellow fever receptive area - area in which yellow fever dose not exit, but where conditions would permit its development if introduced.As an international measure airports and seaports are kept free from the breeding of insect vectors over an area extending at least 400 meters around their perimeters.The aedes aegypti index' is kept below 1.