Slowly these are dying and falling off.

Ashok I agree with Sreekanth M and also check for the attack of Melon Fruit Fly.

Thank you both. Zahirul are there any insecticides available for melon fruit fly ?

Ashok You can use pheromone traps and poison baits. If not controlled then apply Cypermethrin insecticide.

Thank you for the suggestion. Infact i have planted both traps and baits at the time of flowering stage only. Now i will try cypermethrin.

Ashok You are always welcome.

May be temperature effect