Why only female anopheles mosquitoes causes malaria and not male mosquitoes?

1) Males do not feed on mammalian blood. They use their proboscis or feeding tube to drink nectar from flowers.

2) Females seeks mammals, including humans, for blood, which contains the requisite amount of protein to feed her developing eggs. 

The female mosquito lays 30-150 eggs every 2-3 days. Human blood is needed to nourish these eggs and Anopheles shows the most regular cycles of blood feeding and egg laying.The female mosquito has a specialised apparatus to penetrate the skin of its victim. At the end of the slender proboscis, there are two pairs of cutting stylets that slide against one another to slice through the skin. Once through the skin, the mosquito’s proboscis begins probing for a tiny blood vessel. If it does not strike one on the first try, the mosquito will pull back slightly and try again at another angle through the same hole in the skin. Inside the proboscis are two hollow tubes, one that injects saliva into the microscopic wound and one that withdraws blood. The mosquito’s saliva includes a combination of antihemostatic and anti- inflammatory enzymes that disrupt the clotting process and inhibit the pain reaction (so that the victim is unaware of the bite!)

These all features are not available in male mosquitoes hence they cannot transmit Malaria unlike the female Anopheles species.

Only female mosquito can bite

 because only the female can bite while male cannot