In my experience, the spray that matters is the one LEAVING India... and it takes about 30 seconds upon arrival in Mumbai to understand why! I flew through the sparkling new CSA terminal within two weeks of its opening on DL, and the terminal was absolutely infested with mosquitoes. It was the worst we encountered anywhere in Mumbai - although given the location of the airport surrounded by some of the worst housing conditions in the city, it wasn't surprising.
The airport staff were all toting bug zappers - the electrified tennis racket looking things - to try to get the mosquito infestation under control. The most memorable part of that trip: while we were sitting in the lounge, one woman in particular was approaching her job with enthusiasm - passengers were even joining in the fun by pointing out bugs for her to zap.
The part that made it memorable: around the perimeter of the lounge were 5+ shiny new LCD TVs not yet in use. Bug zapper girl happened to chase one of the mosquitoes behind a TV with her tool, only to discover it made a wildly satisfying ZAPzapzapZap! noise - as the electricity from the racket completed a circuit with all the electronics in the TV.
Thinking she'd found the source where all the mosquitoes were spawning from, she eagerly proceeded to scrub every square inch of everything electronic in the lounge with the bug zapper...
Some poor warranty repair guy at Sony analyzing the product failures resulting from that must have been VERY confused as to how their product got caught in an epic lightning storm...
Moral of the story - standing water doesn't necessarily have to be directly in the airplane for aviation to be affected. If the surrounding conditions around the airport are poorly maintained enough, the infestation can spread... I have the DL boarding pass I used as a fly swatter in the club sprinkled with mosquito carnage to prove it.
(I hope that the CSA airport authority has gotten the mosquito problem under control since the airport opened - perhaps those who've visited more recently can share their experiences...)