Who needs mosquitoes?

Back in July Nature ran a news feature on A world without mosquitoes, in which the general desirability and feasibility of mosquito eradication was discussed. Kind of a, ‘what have mosquitoes ever done for us?’ Apart, that is, from acting as a super-efficient vector for a multitude of nasty diseases like malaria, yellow fever, and West Nile virus. Now, I agree that we should not a priori rule out any course of action that can reduce the enormous human suffering caused by these diseases, and that no-one regrets the eradication of smallpox, say. But plans to eradicate insects that can be numerically extraordinarily abundant within an ecosystem, in both the aquatic and terrestrial stages of their lifecycles, set ecological alarm bells ringing loud in my head.

It seems I’m not alone, judging by the lively correspondence appearing in print last week, as well as comments on the online version. Stephen M. Smith (Dept. Biology, Waterloo, Ontario) writes of his astonishment at ‘the hubris of the mosquito experts… who believe the ecological consequences of an extinction would be minor, nil, or quickly compensated’, and I tend to agree, based on quotes like this from the original article:

If we eradicated them tomorrow, the ecosystems where they are active will hiccup and then get on with life. Something better or worse would take over (Entomologist Joe Conlon, American Mosquito Control Association, Jacksonville, Florida; my italics)

If you pop one rivet out of an airplane’s wing, it’s unlikely that the plane will cease to fly (Steven Juliano, Illinois State University, Normal; a monumentally unfortunate choice of words, given the Ehrlichs’ famous rivet popper essay in their book on extinction)

And from the main text:

Most mosquito-eating birds would probably switch to other insects that, post-mosquitoes, might emerge in large numbers to take their place [my italics]

Ultimately, there seem to be few things that mosquitoes do that other organisms can’t do just as well

History is littered with the disastrous consequences of well-meaning ecological meddling (very relevant here is the story of malaria eradication in the US, DDT, and its effects on bird populations, so beautifully described in Silent Spring), and so the fact that ‘there is not enough evidence of ecosystem disruption here to give the eradicators pause for thought’ should certainly worry us (shouldn’t we always, anyway, pause for thought?). But there is another angle to this debate, which raises some intriguing questions.

Conservation organisations are rapidly adopting an ecosystem services approach, whereby we conserve nature because of the bounty with which it provides us (fish to eat, clean water, climate regulation, psychological wellbeing, and so on and on). Mosquito eradication can thus be framed in a more utilitarian way: do they provide us with any benefits? Sure, adult mosquitoes are major pollinators (but not of major crops), but other than that? As medical entomologist Janet McAllister (Centers for Disease Control & Prevention, Fort Collins Colorado) puts it in the original article, ‘If there was a benefit to having them around, we would have found a way to exploit them’. This point is picked up in the correspondence by Fern Wickson (Genøk Centre for Biosafety, Tromsø, Norway) who asks,

…what else might we reasonably eliminate from the face of the planet – deadly snakes, plague locusts? …ecologists have to ask what minimum level of biodiversity is required for functional provision of ecosystem services to sustain humanity.

It is not clear to me whether Wickson is advocating this kind of audit, or simply raising it as the logical endpoint of the eradication stance, but it is a really important question: how far should we go in deciding which species ‘deserve’ to share the planet with us?

Even within the mosquitoes this is complex. There are, after all, around 3500 species, only a few of which are a health hazard. So should we eradicate the malaria-carrying Anopheles species? What about Aedes aegypti, which carries yellow fever? And if those, why not the bloody midges that can ruin Scottish holidays? Or the wasps which seem to exist only to cause havoc at picnics (although of course they are much more important – see buglife’s new Stop Swatting Wasps campaign).

It’s a question conservation biologists are not very good at addressing, because there is no objective, scientific answer: where do we start managing nature? And where do we stop?