Just as I sit watching one more entomologist stating the most popular dengue “fact” that Aedges aegypti, dengue’s mosquito-vector, lays its eggs in clean water, I am forced to see a sort of symbolism in it.
We always fail to understand that devil is always in the details, and it is this lack of scientific vigor that defeats all our endeavors.
If my editor permits, I would rather utilize this column space to state following sentence in largest possible fonts, as it is this single detail that makes Aedges aegypti very special, and it also defeats the administration’s main advisory of “emptying the water from containers”.
Aedges aegypti lays its eggs, not IN water; but sticks them ABOVE waterline on the wall of water containers.
Though it sounds innocuously simple, it is a tale worth telling, purely for showing amazing ability of evolution to get into incredibly complex details. Life has survived for nearly four billion years, and evolution of Aedges aegypti’s oviposition preference is one of the examples that tell us Why.
Most mosquito species lay their eggs in water purely because larval stage of this insect is aquatic. For most outdoorsy mosquito species, life is uncomplicated as they have linked their lifecycle with rain and use water bodies formed post-rain. By laying eggs in such pools, they are assured of water being available for the larvae.
Aedges aegypti is not so lucky because it has left rainwater-filled tree-holes of African forest and moved indoors with us. It is a big-game hunter turned city-sleeker that uses flowerpots and water-coolers.
Domestication has provided Aedges aegypti with a sheltered life but it has complicated the issue of water availability for the larvae because it is forced to depend on human-filled water containers for egg-laying. But, Aedes aegypti solves this problem by an amazing strategy.
Instead of laying eggs IN the water like other mosquitoes, it sticks its eggs ABOVE the waterline. This looks like a counter-productive move as the eggs remain dormant till flooded with water, but it works wonderfully because, being above the waterline, the eggs are activated only when additional water arrives in the container. Arrival of more water increases the possibility for the larvae to have enough water to survive and develop into adult mosquito.
And it is this very adaptation that has also forced Aedes aegypti to evolve something even more dangerous. Out the necessity of being able to remain dormant, Aedes aegypti has evolved eggs capable of surviving dry conditions for months like microscopic time bombs ready to be activated when water arrives.
Unfortunately for us, dengue virus has capitalized this egg-dormancy by doing something extremely sinister. Once inside mosquito body, the virus travels down into its eggs and infects the unborn. This means that the progeny of infected mosquito turns in disease carriers from birth. This strategy allows dengue to survive across lean period and reappear when mosquito population is resurrected by arrival of water.
Tales from nature are fascinating because of the complex story-lines that appear as you dig deeper. Nature has spent billions of years refining its products so complexity is common place, but more important aspect of this process is that wars in nature are endless.
At this point, our war against dengue is more like a knee-jerk reaction that has not gone into the real depth of the problem and is unlikely to hit mosquito-parasite duo where it hurts.
If we want to win the war, we need to get scientifically vigorous; as, nature uses evolution as a counter, a process capable of churning out incredibly complex counter-strategies. Research is the real and only key, as this war won’t be won till we manage to get one step ahead of this process.