Bryan Caplan  

Resistance versus Avoidance

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Sunday I declared war on a pair of yellow jacket nests at the base of my house, and it got me thinking. According to conventional wisdom, when I use an anti-yellow jacket spray, I impose a negative externality on other people, because I make the yellow jacket population more resistant to the spray. In Darwinian terms, the yellow jackets that are less vulnerable are more likely to survive, leading the next generation to be less vulnerable.

This is a common counter-argument to those who allege that anti-DDT regulation led to millions of deaths from malaria: You can't do a linear extrapolation, because the mosquitos would have built up resistance anyway. (See also here).

But on reflection, matters are more complex. One way the yellow jacket population might adapt to spraying is to build up resistance. But there is another adaptation that seems at least as likely: Learning to fear human beings and avoid nesting near human settlements.

Think about deer. People have been hunting them for ages. And they have built up very little resistance to bullets. In part, this is because our technology advances faster than they can adapt. But the main reason is that deer have largely adapted in a different direction: Running like deer at the first sight of us.

The interesting thing about the adaptation of "fearing humans" is that it is actually a positive externality of my spraying. When I kill yellow jackets who get too close to my house, it also makes yellow jackets less likely to nest near my neighbors' houses.

You might think that the adaptation route would depend on animal species' generational cycle. The shorter-lived the animal, the more rapidly they adapt. (Think of bacteria). But it's not clear why this would make one kind of adaptation more likely than the other. (Of course, if animals actually learn, rather than simply making the evolutionary cut, then it's a different story. An animal can learn to fear man, but not to survive toxic sprays).

The net effect of these negative and positive externalities? It could go either way, and presumably varies from case to case. Until I've got good evidence one way or the other, my motto shall remain: Spray and let spray.


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COMMENTS (10 to date)
Jacqueline writes:

Do yellowjackets have enough brains to distinguish between human settlements and other areas?

dsquared writes:

Since ordinary bees have managed to hang around for approximately a million years without learning that they die when they sting warm-blooded creatures, I think that you are on a hiding to nothing with respect to this one.

Danno writes:

The reason that we don't have bulletproof Deer (and also the reason why if you're EVER prescribed an Anti-Biotic, you NEED to take it for the full prescription period) is that the number of Deer that survive a bullet wound is much much lower than the number of bacteria that survive exposure to anti-biotics. It's a better idea to think of a colony of bacteria as an organism rather than the single cell in this case because through the process of subsequent partial elimination of the colony, the bacteria that have made it that far have had the best ability to survive the circumstances that have been wiping out the rest of the colony.

I dunno if that's applicable to Yellowjacket swarms or not though because I thought only the Queens of those sorts of hives could breed.

Anyway, I thought the best way to deal with Yellow Jackets was a flamethrower.

John P. writes:

I would throw two other things into the mix: (1) Your spraying of yellow jackets on your property lowers the overall population and therefore lowers the chance that people/properties beyond you and yours will be stung/infested. (2) The question (which we are presumably unable to answer now) of whether the costs of increased resistance outweigh the benefits of fewer yellow jackets today will be answered by the market if/when increased resistance creates a need for different treatments.

N. writes:

This sounds awfully fishy to me. Adaptive processes are not somehow teleological, which is the way they seem to be described here. Rather, they are random and coincidental based on mutation. An analogy, for instance, between evolutionary advantage and market innovation is not particularly useful. An innovator perceives a need and uses his brain to manipulate the world in some imaginative way to fill it. Evolutionary advantage occurs when the genetic drift of some species just-so-happens to give it a leg up in competition _completely by coincidence_. A species of wasp cannot just "decide" to evolve based on environmental factors.

Consider roaches for example, or rats, both of which are persistent pests in human civilization. It's true that they will become more resistant to poison over time (because those that survive poisoning will go on to reproduce, spreading their poison resistant genes). Yet their *main* competitive advantage, I would argue, is their capacity for swift reproduction and the number of offspring in each brood. That is, they thrive due mostly to other factors than poison resistance per se (although it is true that the more ratlings and roachlings, the faster poison-resistant genetics are spread).

It is also, I think, at the very least, contraversial that any species -- even and perhaps especially humans -- can transfer a "learned fear" of something cross-generationally. Especially when there may be overwhelming advantages for a species to live around the very thing that they fear (I have a hunch that wasps may find superior building materials for their nests around human settlements than they do elsewhere, but that is pure speculation on my part).

Many useful comparisons can be drawn between biology and economics, but I think the thesis of this particular comparison is false.

Besides, Bryan should know perfectly well that the more effective method to deal with wasps is to cast the fourth level Cleric spell Repel Insects; although, to be fair the duration is only 1 turn/level. Since Bryan's gotta be at least a 16th level Disciple of Hayek or whatever, it should still provide him with at least some respite.

bernard Yomtov writes:

I suppose that what makes one kind of adaptation more likely than another is the amount of mutation needed. I suspect that the amount of DNA change that would make wasps avoid humans is astronomically improbable, while the amount that lets them survive a particular insecticide is not. It may even be impossible for wasps to undergo the "fear humans" mutation and still remain wasps.

And of course nesting near human settlements might well have survival value in terms of, say, availability of food.

All that said, I'm no biologist, so all this conjecture is based on very limited understanding.

Zubon writes:

It seems perfectly reasonable that fear can be bred into a species by eliminating the members less inclined to it. Some part of the psychological condition must be congenital, even if it is only a proclivity. Which deer survive? The more skittish ones, the ones who are better at detecting and fleeing humans, etc. If humans are excessively afraid of spiders and snakes, perhaps the early humans without those fears met some poisonous ones and therefore bred less (idle speculation that smacks of urban legend, but inborn fear would seem to have some survival value).

In terms of building up resistance, the important factor is to overdo it so that you get all of them. People stop taking the anti-biotics when they feel better, and the bacteria builds up resistance; people keep taking the anti-biotics well after feeling better, and it wipes out even the resistant ones. By that logic, you can prevent the externality by continuing to spray for a while after you have the wasps down to a comfortable level - overwhelm the resistant ones, too, even if they are so few that they would not bother you *now.*

jn writes:

One thing re: DDT and other insecticides.

It turns out that spraying can be useful even if the mosquitoes develop resistance.

The repellent effect of indoor spraying substantially lowers the transmission rates of malaria even if the mosquitoes don't die from the spray. In this case, NOT spraying your house imposes a negative externality on others because the mosquito needs to bite a human within two weeks of having picked up the malaria virus from biting a human earlier.

Keeping them out of houses with indoor spraying lowers the density of human contact and lowers the chance that the mosquito bites a human outdoors with the virus then bites another within a few weeks. This then leads to huge benefits (in terms of defeating malaria) even in areas where the mosquitoes have developed resistance.

It doesn't directly address your points, but it adds an interesting complication to these thought experiments.

Bob Knaus writes:

I'm not an expert in anything, but I have plenty of relevant experience in observing animals.

Bees can be bred to be more or less tolerant of humans. The ones my uncles raise for honey are much less inclined to sting than "Africanized" bees (the "killer bees" of Hollywood). Presumably, other closely related insects such as wasps could have similar heritable traits to avoid or attack humans.

Fish can "learn" to alter their behaviour towards humans rather quickly. At a local reef here in the Abacos where they are fed by snorkelers, fish will swim right up to your mask for a handout. The same species a half-mile away will avoid you, as they would any large predator. This behaviour has developed in less than 30 years.

Similarly, deer who are not hunted and have no natural predators lose their fear of humans. I have watched a doe and her fawn walk into a clearing in Everglades Park no more than 10 feet away from me. This amazed my cousin from Pennsylvania who was with me. He hunts them every fall, and had never been that close to a live wild one. Again, this behaviour has developed in only a few decades.

It seems to me that the difference between fearing and not fearing humans must be a pretty small one from a genetic perspective, and also that both behaviours must be fairly common in the gene pool of most animals, given the speed at which this differentiation appears in so many species.

Harold writes:

Even in the case of mosquitos developing resistance, DDT still acts a repellent:

"This avoidance behavior, exhibited when malaria vectors avoid insecticides by not entering or by rapidly exiting sprayed houses, should raise serious questions about the overall value of current physiological and biochemical resistance tests. The continued efficacy of DDT in Africa, India, Brazil, and Mexico, where 69% of all reported cases of malaria occur and where vectors are physiologically resistant to DDT (excluding Brazil), serves as one indicator that repellency is very important in preventing indoor transmission of malaria."

[See, e.g., J Am Mosq Control Assoc 1998 Dec;14(4):410-20; and Am J Trop Med Hyg 1994;50(6 Suppl):21-34]

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