Would eliminating mosquitoes really have no ill effects?

We close the week on the same subject with which we opened it, the mosquito. A short piece in this week's Nature asks whether eradicating the mosquito would have any serious ecological consequences. (The photo of mosquito larvae in a pond is from the article: M.and P. FOGDEN/MINDEN PICTURES/FLPA.) There are 3,500 named species of mosquito, and in only a few hundred do the females require a blood meal to reproduce and an even smaller subset of those cause disease in humans. But of course they are major causes of disease.

Malaria infects some 247 million people worldwide each year, and kills nearly one million. Mosquitoes cause a huge further medical and financial burden by spreading yellow fever, dengue fever, Japanese encephalitis, Rift Valley fever, Chikungunya virus and West Nile virus. Then there's the pest factor: they form swarms thick enough to asphyxiate caribou in Alaska and now, as their numbers reach a seasonal peak, their proboscises are plunged into human flesh across the Northern Hemisphere.

It's been said that malaria has killed more people in history than any other disease. And as climate changes, the distribution of mosquitoes will also change, perhaps affecting (and infecting) populations that are now free of the problem.

So, Nature asked a number of scientists who work on various aspects of mosquitoes and mosquito control what would happen if they were eliminated, hard as that is to do. The scientists basically shrugged their shoulders at the ecological consequences, and said they'd love to see it happen. There might be 'collateral damage', in terms of a hole in the food chain for some fish or birds, or a missing pollinator for many plants, but those polled said the gaps would be quickly filled by some other organism, and humans would be a lot better off for it, even if it did mean human population increase through disease control.

Ultimately, there seem to be few things that mosquitoes do that other organisms can't do just as well — except perhaps for one. They are lethally efficient at sucking blood from one individual and mainlining it into another, providing an ideal route for the spread of pathogenic microbes.

This nonchalance set us to wondering -- is this a human-centric view that lauds the benefits of mosquito extinction to us and dismisses serious consequences to other species, or is it true that if this not insignificant biomass were eliminated it wouldn't be missed? We don't really know, of course, but we suspect it's a bit of both. We've written before about how science tunnels through truth, streamlining a problem until it is tractable by the methods at hand. It's difficult if not impossible to understand all the interactions within a complex ecosystem, and so surely it's not possible to predict all the consequences of mosquito elimination. And certainly history suggests this is the case.

But a fundamental principle of life is facultativeness, the ability of an organism to adapt to changing circumstances. Any species that has evolved to subsist on only one food source is extremely vulnerable to the vicissitudes of environmental change, so it's plausibly true that most birds or fish that now make mosquitoes and mosquito larvae a large part of their diet could quickly find and depend upon a different food source, and new pollinators would fill that need as well. The classic idea of the exquisite adaptation of all species to their circumstances, through natural selection, argues against this, but as we've written many times before, that idea is oversubscribed.

To date, however, in spite of the best efforts of people who've spent decades working on the problem, mosquitoes are proving to be damn near impossible to eradicate. At best, we'd have to poison ourselves and much else with insecticides to do it--or we'll need genetic means of attack such as we've posted about recently, that don't harm anything but the biters themselves. As the Nature piece puts it, "...while humans inadvertently drive beneficial species, from tuna to corals, to the edge of extinction, their best efforts can't seriously threaten an insect with few redeeming features." So the question is moot for some time to come.  But it's an interesting one.