Aedes aegypti and other mosquitoes have a complex life-cycle with dramatic changes in shape, function, and habitat. Female mosquitoes lay their eggs on the inner, wet walls of containers with water. Larvae hatch (picture 1, inset) when water inundates the eggs as a result of rains or the addition of water by people. In the following days, the larvae (picture 2) will feed on microorganisms and particulate organic matter, shedding their skins three times to be able to grow from first to fourth instars. When the larva has acquired enough energy and size and is in the fourth instar, metamorphosis is triggered, changing the larva into a pupa (picture 3). Pupae do not feed; they just change in form until the body of the adult, flying mosquito is formed. Then, the newly formed adult emerges from the water after breaking the pupal skin (picture 4, inset). The entire life cycle lasts 8-10 days at room temperature, depending on the level of feeding. Thus, there is an aquatic phase (larvae, pupae) and a terrestrial phase (eggs, adults) in the Ae. aegypti life-cycle.
It is this life-cycle complexity that makes it rather difficult to understand where the mosquitoes come from. Similar complex life-cycles with aquatic and terrestrial forms are observed in amphibians. For educational and training purposes, it is rather useful to make life-cycle kits, so people have an opportunity to watch how the aquatic stages turn into terrestrial ones.
There is a very important adaptation of dengue vectors that makes controlling their populations a difficult task. Their eggs can withstand desiccation for several months, which means that even if all larvae, pupae, and adults were eliminated at some point in time, repopulation will occur as soon as the eggs in the containers are flooded with water. Unfortunately, there is no effective way to control the eggs in containers.