The symbiosis between mosquitoes and the microorganisms responsibles of disease is endosymbiosis.
Explanation:
Mosquitoes usually have different microorganism inside their digestive tract. When mosquitoes suck other animals blood, their transmit those microorganisms (frequently parasites) to the animal. In these cases mosquitoes are called vectors, organisms that have microorganisms (endosymbionts) inside but do not suffer any consequences, they only act as a house for the endosymbiont.
a method of procedure that has characterized natural science since the 17th century, consisting in systematic observation, measurement, and experiment, and the formulation, testing, and modification of hypotheses.