Yesterday’s New York Times reports a series of studies, funded by the Bill and Melinda Gates Foundation, aimed at eradicating malaria (one report has appeared in Malaria Journal; the reference is given below and you can download the paper by clicking the link at the NYT).
The idea is a clever one: female mosquitoes, who are the carriers of malaria (females need a blood meal before laying eggs), also dine, between bites, on nectar or fermenting fruit. Scientists were able to kill more than 90% of mosquitoes in tests in Africa simply by spraying trees with “poison nectar”: a mixture of sweetened water and an insecticide derived from bacteria. (The insecticide is Spinosad, which has the advantage that, because it must be ingested to kill, it’s harmless to humans and many other insects.) Artificial baits containing poison and sweet liquid were also effective.
The researchers note two problems, but are missing one:
Two more concepts still need to be tested, experts said.
Although it clearly works in arid areas where there are few trees or flowers, will it work in jungles, forests or farms where there are many competing sources of nectar?
And how often does spraying have to take place? The inventors hope as seldom as once a month will do the job.
Yes, but they’ve also forgotten about natural selection, for those mosquitoes that aren’t killed by Spinosad will be the ones who produce offspring, so we might expect mosquitoes to evolve resistance to the poison. This, of course, happened with mosquitoes and DDT in many parts of the world.
This might not happen, however, with an alternative poison that they’re using: boric acid.
“You can buy it by the truckload,” Dr. Christensen said. “And it kills in so many ways that there’s never been resistance to it. Some authorities think there never will be.”
Boric acid, which is often used to control cockroaches, is considered nontoxic to humans, but in insects acts both as a stomach poison and a cuticle abrasive, causing death by starvation or dehydration.
Frankly, I’m surprised that roaches haven’t evolved resistance to boric acid, for if there’s any rule in controlling pests and bacteria, it’s that there’s almost always genetic variation in a pest that enables it to respond to a novel selection pressure, so our counter-pest measures are temporary at best. Nature is cleverer than we are, and we simply can’t predict the multifarious ways that insects can respond to insecticides, bacteria to antibiotics, or weeds to herbicides.
And genetic variation is pervasive: I’m aware of only a handful of selection experiments in Drosophila, for example, that haven’t produced a response (two of the three “failed” studies were done by me, and those involved selection for directional asymmetry, for example, flies whose left eyes were bigger than their right, or vice versa).
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Müller, G. C. et al., 2010. Successful field trial of attractive toxic sugar bait (ATSB) plant-spraying methods against malaria vectors in the Anopheles gambiae complex in Mali, West Africa. Malaria Journal, 9:1-7
Sadly the problem is that the researchers only see the problem of malaria. They do not appear to see the collateral damage of interfering with the food chain from what I have read.
1 What other insects will be harmed?
2 Are mosquitoes beneficial as pollinators – a quick look seems to show this research has not been done (?)
3 What consequences are there for humans if birds & other insect feeders are reduced because of a lower population of mosquitoes? Will human food sources in those areas be impacted on by that?
My number 3 may be off – a further look suggests that mozzies are not a major food source for birds but I wonder if that is based on real research rather than an assumption. Not sure how you could ever measure that unless you had a secure cage & released various insect types & an insect eating bird to see what they prefered to catch. Mosquitoes are pretty small of course. Perhaps being small is a useful adaptation as it means they are less nutritious for a predator, that would have to expend far more energy foraging to make up for the small size. Never thought of that before… Natural Selection is so amazingly simple yet complex!
Usually you find out about these things by examining feces or gut contents, it’s pretty common although I don’t know if it was done in this case.
Ah – would expect there is little to survive of the insects in the poop (beetles might) but the other method means killing the bird I suppose?
I thought it was common knowledge, that mosquitoes are more annoying than most pests
A blog without preview possibilities is … perverse?
Unlike creationists I think that the world is NOT made for humans & we do NOT have the right to make it cozy for ourselves if that involves the deliberate extermination of other species. We have to accept that some things are unpleasant or difficult for us & live with that.
Thanks for the article. The elimination of mozzies where introduced like Hawaii would save native bird species.
The problem here is that this does not just kill mosquitoes, but any insect that drinks nectar. That is a tremendously important set of pollinators and bird and bat food. See my earlier comment below.
Much as I’d like to agree with that article, it sounds more like opionion, albeit expert opionion, than proof.
Just from personal observation, I’d expect mosquito larvae to be quite an important food source in ponds, etc.
It’s plausible that the method of killing is such that evolving a natural resistance is simply implausible. After all, mosquitos have been getting swatted for millions of years, and yet the lazy bastards still haven’t managed to evolve an immunity to blunt force trauma…
Or bleach. I’m unaware of any microbe that’s developed a tolerance to bleach.
The challenge isn’t killing nasties; we could do that with H-bombs if nothing else. The challenge is killing the nasties and only the nasties while not causing any harm to the non-nasties.
As Dominic observed, mosquitoes are far from the only nectar feeders out there. What will this do to all those other nectar feeders? Bees? Moths? Hummingbirds?
Cheers,
b&
Chlorine bleach? Try giardia and cryptosporidium. If only microbe and fungus control were as easy as using chlorine and formaldehyde.
Dunno about that – around here they’re damned good at dodging.
Yeah, that does seem to be something mosquitoes in certain areas are better at than others, dodging and also predicting swats to get out of the area before they occur, which might also have something to do with how fast they have evolved to suck. There is also the size factor that makes it hard to even see some of them before they have bitten you and the other angle of attack which is to overwhelm you by swarming so you can’t swat all of them. Or maybe I’m just getting older… damn mosquitoes.
Wow, what a disaster for the local ecosystems–poisoning virtually all insect pollinators! Even from an anthropocentric perspective, that has got to be crazy. Insect-pollinated crops are important to most cultures. The implications for ecosystem functioning are enormous too—many plants will fail to set seed, leading to a shift to non-insect-pollinated plants. I can hardly think of a more heavy-handed and ecologically destructive approach.
Spinosad is commercially available against lepidopteran larvae and thrips. Thrips are already showing resistance in the US. There is no magic bullet pesticide.
The goal here is presumably not to eradicate mosquitoes, which seems a daunting task, but to eradicate the malarial parasite. Maybe the thinking is to force the mosquitoes through a temporary population bottleneck in order to deny the parasite a vector. Then once the parasite is extinct, the mosquito population could be allowed to rebound. I’m not a biologist and have no idea whether this would work (and the article isn’t very clear on this point), but maybe this sort of strategy could minimize the problem of evolving pesticide resistance in mosquitoes.
Of course they don’t have to evolve a resistance to the poison. We’ll just select for a population that doesn’t like the smell.