What public health measure used by Europeans in the tropics drastically reduced troop death rates from both malaria and yellow fever?

Question

Quizplus · Accepted Answer

Mosquito eradication efforts, including draining swamps and using insecticides, significantly reduced the populations of mosquitoes that transmit malaria and yellow fever, thereby drastically lowering death rates from these diseases among European troops in tropical regions.

What Public Health Measure Used by Europeans in the Tropics