Step 1: Understanding malaria transmission.
Malaria is a protozoan disease caused by species of {Plasmodium}. The parasite requires two hosts to complete its life cycle: a human and an insect vector.
Step 2: Role of mosquito.
The female {Anopheles} mosquito acts as the vector and definitive host of the malarial parasite. It transmits the parasite to humans while feeding on blood.
Step 3: Analysis of options.
(A) Honey bee: Not a disease vector.
(B) Housefly: Mechanical carrier for some diseases, not malaria.
(C) Round worm: A parasite itself, not a vector.
(D) Mosquito: Correct, required for transmission of malaria.
Step 4: Conclusion.
Transmission of malarial parasite requires a mosquito vector.