The correct answer is option 3: Sandfly.

Option 1: Fruit flies are not known to spread Kalaazar. They are commonly found near fruits and vegetables, and while they can be a nuisance, they do not transmit diseases like Kalaazar.

Option 2: Tsetse flies are responsible for spreading African trypanosomiasis, also known as sleeping sickness. They are not known to spread Kalaazar.

Option 3: Sandflies are the main culprits in spreading Kalaazar. These small, blood-sucking insects are prevalent in areas with poor sanitation and affect humans and animals by transmitting the parasite that causes Kalaazar.

Option 4: While mosquitoes are notorious for spreading diseases like malaria, dengue fever, and Zika virus, they are not the primary spreader of Kalaazar. Sandflies, not mosquitoes, are the insects responsible for transmitting Kalaazar.

Therefore, option 3, Sandfly, is the correct answer.