by Brian Tomasik
First published: fall 2007; last update: 20 Mar. 2017
It is not known whether insects can feel pain, but even if we assign this possibility a low probability, the large number of insects alive makes the expected value of their suffering considerable. In particular, in this piece I investigate the cost-effectiveness of trying to reduce the expected amount of suffering by agricultural pests through promotion of less painful insecticides. While I don't necessarily think pesticides cause net harm, since they may prevent the existence of lots of insects that would endure net suffering in the wild, either way, killing insects more humanely would prevent suffering. An inefficient brute-force strategy would be to directly pay farmers to use pesticides that cause faster and more benign deaths. Under plausible assumptions, each dollar used for this purpose would prevent the expected equivalent of 250,000 experiences of being killed by the original, more painful pesticide. Of course, funding research or advocating policy changes would likely be more cost-effective than this direct approach.
This back-of-the-envelope calculation is mainly a theoretical existence proof for the possibility of reducing insect suffering in a cost-effective way. To take a first baby step in that direction, I asked entomologist Jeff Lockwood for his thoughts on which insect-control methods are more or less painful.
Note: This piece should not be construed as supporting organic crop farming. For one thing, organic fields have much higher insect populations than pesticide-sprayed fields, and hence they create much more natural death. Furthermore, "organic" pest-control methods like introducing natural insect predators, spraying Bt, and other biological-control strategies are probably some of the most painful. While we can obviously reduce the immense suffering caused by human pesticide use, this doesn't mean that conventional pesticides are necessarily net bad for insects; whether conventional pesticides prevent more suffering than they cause is an interesting open question.
I do worry that the "humane insecticides" idea might cause net harm if applied naively, because it could result in lower mortality for non-target insects, thereby increasing their populations and causing more painful natural deaths.
- 1 Summary
- 2 Background
- 3 Paying farmers to use different pesticides
- 4 Further questions to explore
- 5 Jeff Lockwood's speculations on relative painfulness
- 6 Does insecticide use in general increase or decrease insect suffering?
- 7 Why insecticides may be better than other control methods
- 8 Is it good or bad to kill non-target bugs?
- 9 Acknowledgments
- 10 See also
- 11 Footnotes
The evidence is mixed on the question of whether insects can feel pain. A fair number of papers have investigated this topic, but two in particular that have good reviews of the literature are Jane A. Smith, "A Question of Pain in Invertebrates," ILAR Journal, and Jeffrey A. Lockwood, "The Moral Standing of Insects and the Ethics of Extinction," Florida Entomologist. As Smith notes, "The well-being of invertebrates used for research is being taken increasingly seriously," with V.B. Wigglesworth, "Do Insects Feel Pain?", Antenna, suggesting that we should assume insects can suffer unless we have evidence proving otherwise. I would discourage this precautionary-principle approach in favor of a more conservative Bayesian expected-value approach, but it seems clear to me that it would be wrong to completely ignore the possibility of insect pain until we have more information.
Suppose we decide on a relatively conservative probability that insects feel pain of 0.01. At any given moment, the earth contains 1018 ("a billion billion") insects, so even multiplying by 0.01, there are 1016 "expected insects." Considering that insects live very short lives, and that most insect offspring die long before reaching maturity, it's plausible that insect lives contain far more suffering than happiness. See "The Predominance of Wild-Animal Suffering over Happiness: An Open Problem (pdf)." Given the difficulty of finding a satisfactory solution to wild-insect suffering, it may be tempting to throw up one's hands and say, "Yes, wild insects probably endure a lot of unnecessary pain, but there's nothing we can do about it." This may or may not be the case, but either way, such an attitude ignores areas in which we could clearly make a net positive reduction in insect suffering -- regardless of whether wild insect lives are worth living.
As suggested by Wigglesworth, one area where insects may suffer preventably is in the laboratory; Smith reviews principles for improving care and treatment of such insects. But the numbers of insects involved here is relatively small by comparison to, say, the insects killed by pesticides. One's immediate reaction to this fact might be to try to limit use of pesticides on farms and lawns so that humans kill fewer insects. However, if insect lives aren't worth living, this may be precisely the wrong thing to do, since the insects killed by pesticides would have died in other (probably painful) ways, and pesticides prevent -- at least temporarily -- the existence of new insects that would otherwise have lived miserable lives.
The issues raised above need to be explored, but they do not automatically imply that we should throw up our hands and move on to other issues. In the remainder of this piece, I'll explore the cost-effectiveness of trying to promote use of pesticides that kill insects more quickly and less painfully. While quite arguably not optimal, this approach to relieving insect suffering avoids the thorny issue of whether insect lives are worth living and whether we should kill more or fewer of them. As such, the numbers here should represent a lower bound on the cost-effectiveness of using resources to address insect pain. If these numbers compete in cost-effectiveness with other possible uses of time and money, then even more efficient measures to reduce insect suffering could only be more urgent.
The "pesticides" referred to here needn't be chemical in nature; they could, for instance, be biological control agents, often used in organic and integrated-pest-management systems. To give one example: Ichneumon wasps are sometimes used to control flies and beetles. However, these parasites eat their prey while still alive out from the inside over an extended period. If the hosts do feel pain during this process, it is likely severe and protracted, which suggests trying to dissuade farmers from using this method. On the other hand, the fact that the host doesn't respond aversively during the process (I don't think) may imply that it lacks pain receptors to its internal organs, similarly to the way in which human viscera have few such neural connections. (This is just a conjecture on my part.) In this case, perhaps ichneumon wasps would be a humane alternative, unless the final stages of consumption of the host, affecting its external parts, is still painful. Ichneumon wasps are just one of several pest-control parasites that consume their prey in the same fashion -- and which may therefore be potential targets for replacement.
Paying farmers to use different pesticides
Suppose we think that pesticide A causes death to the insects that it kills twice as quickly as pesticide B and that the two pesticides are equally painful per unit time. Suppose also that both are equally potent at killing target and non-target bugs. (If this is not true, then the calculation becomes much more difficult.) If farmers currently use pesticide B because pesticide A is more expensive, then we could set up a program to compensate farmers for switching to use of pesticide A. This scheme seems highly inefficient by comparison to other approaches, but it is direct and avoids concerns that some might have about whether simply doing research or advocacy would really make any difference.
Define the following variables:
- p: our subjective probability for how likely it is that insects feel pain. This is likely to vary from species to species, but I ignore that complication here.
- n: the average number of insects (and other small sentient organisms, if any) that inhabit a hectare of crop land during the growing season. In practice, this is likely to vary from one type of crop to another and one region to another.
- f: the fraction of the above insects and other organisms that are killed (or otherwise suffer significantly) as a result of applying pesticides.
- s: the average ratio of the painfulness of the more humane pesticide to the less humane pesticide (e.g., s = 0.5 in the previous example, because pesticide A is half as painful as pesticide B). The percent by which suffering of death is reduced by using the more humane pesticide is (1-s)*100%.
- c: the dollar amount by which it's more expensive to spray a hectare of cropland once with the more humane pesticide rather than of the less humane one.
Suppose we spend c dollars to compensate a farmer for using a more humane pesticide on a single hectare. The expected number of insects benefiting is pnf, and they each avoid suffering an amount of suffering equal to 1-s times the painfulness of death by the more painful pesticide. Our expected reduction in suffering per dollar R is then
R = pnf(1-s)/c
expressed in units of "expected equivalent number of experiences of death by the more painful pesticide prevented per dollar."
Note that this calculation ignores
- fixed costs to research candidate insecticides that are less painful but equally lethal
- administrative costs to manage an organization dedicated to subsidizing humane insecticides
- costs to connect with farmers and find willing farms
- costs to monitor compliance and measure effectiveness.
Next, I suggest plausible subjective probability distributions for each of the five parameters. With that, I compute a numerically approximated probability density function for R. (Note that it's formally incorrect to assign a probability distribution to p, but I wanted the results to convey a sense of how cost-effectiveness changes depending on whether p is set high or low.) Readers can recompute the results using their own subjective probabilities using this Excel workbook.
- ln p is uniform on [-6, -0.5]
I think 0.6 ~= exp(-0.5) is a high estimate for p. 0.002 ~= exp(-6) seems like a low estimate.
- ln n is normal with mean 15 and standard deviation 2
An expert friend of mine estimates that a hectare of insect-infested crop land would have between 500,000 (natural log ~= 13) and 50,000,000 (natural log ~= 17) insects, depending on the type of crop and type of insect.
- f is normal with mean 0.8 and standard deviation 0.05
The same friend estimates 0.8 as reasonable. "The Estimation of Insect Density and Instar Survivorship Functions from Census Data" by Martin Birley (JSTOR link) assumed 10-20% survivorship when a sugar-cane pest was sprayed with residual insecticide (p. 503).
- s is uniform on [0.3, 0.9]
This is speculation.
- c is uniform on [1, 8]
I don't have excellent data on this. What I did was to look at the cost of "chemicals" per acre for various types of crops using the USDA's surveys of Characteristics and Production Costs. Roughly, chemical costs per acre for wheat ranged from ~$3 to ~$9, for soybeans from ~$22 to ~$29, and for corn from ~$20 to ~$30. I'll assume a uniform distribution between $3 and $30. But this is in $/acre. Noting that one acre is 0.4047 hectares, this becomes a uniform distribution between $7.4 and $74. It's not clear how many chemical sprayings per year this represents; I assume 1.5. It's also not clear how many other chemicals (fertilizers, herbicides, fungicides) this includes; I'll assume 1/3 of all chemicals are insecticides. I also assume that switching to the more humane insecticide would increase total chemical costs by 50%. The result, after liberal rounding, is a uniform distribution on [1, 8].
The expected number of death-experiences prevented per dollar is around 250,000. If death by pesticides is as bad as spending, say, 2 days in a factory farm, this is like preventing 1,369 years of suffering for animals in factory farms per dollar. The cost to prevent a year of suffering is then $0.0007.
What would the figures be if a very conservative value were used for p? Take p = 0.001. Then the expected value is roughly 2,100, which still translates into a cost of $0.09 to prevent a year-equivalent of factory-farm suffering.
Further questions to explore
- How do current insecticides kill? How painful is it?
- How do insects not killed by insecticides die? How painful is that?
- How many insects are affected by insecticide spraying per hectare?
- What are the costs to switch control methods?
- How are populations of target and non-target insects affected? The ideal case is to find insecticides that don't increase non-target populations.
- What would success look like in a humane-insecticides campaign? Humane labeling?
Jeff Lockwood's speculations on relative painfulness
On 4 Dec. 2011, I asked entomologist Jeff Lockwood the following questions:
What's your tentative rank order for the humaneness of insect-control methods?
Also, I'd like to support research on this question [...]. How would you recommend beginning that process? Would I contact professors and grad students to see if one of them would be interested in writing a paper on the topic? (Maybe for an ethics journal or maybe a more science-based one.)
Suppose the effort got a little more traction. How would we then go about advocating for the use of humane insecticides? For example, imagine that the Humane Society got interested in the cause and wanted to run a campaign. What could they do? Maybe find and support farms willing to switch to the better methods? Ask schools to buy from those farms (similar to the current cage-free-egg campaigns)?
As for a tentative rank order for the humaneness of insect control methods, that's a real challenge! But let me try a very 'soft' ranking:
- Cultural control: Preventing insects from occupying a resource (e.g., habitat modification) seems the most humane approach as no beings are directly harmed (at least when this is possible). [Brian adds: Humane cultural-control methods include crop rotation and sanitation. These approaches seem good because they reduce total insect populations. Likewise for repellants and such.]
- Physical control: [... Some] forms of physical control would likely cause suffering (e.g., picking and crushing) but the duration would be relatively brief.
- Biological control - predators: Death from predators is often relatively rapid, although this is not certain. Larger predators (e.g., birds or skunks) are rather more efficient in their killing than small predators (e.g., ants or beetles). [Brian thinks predation is more painful than this, because the suffering would seem to be extremely intense per unit time, and evolution should have molded insects to regard being eaten by a predator as one of the worst things that could possibly happen.]
- Chemical control - neurotoxins: Depending on the dose, it appears that death comes quickly. Of course, at low doses the individual may be rendered physiologically and behaviorally dysfunctional and prone to a slow death. It should also be noted that many non-insect species are likely to be intoxicated, and these non-target species would substantially lower the ranking of this approach if taken into account. [Brian adds: This assumes they're not better off dead. I think killing non-target organisms may be a bonus because it prevents them from having large numbers of offspring that mostly die, possibly painfully, shortly after birth.]
- Chemical control - growth regulators: The insect, in my observations, often dies very slowly in a protracted state of dysfunctionality during which the individual is highly susceptible to scavengers and small predators. [Brian adds: This page confirms that observation: "The cockroaches [a]ffected by Gentrol look deformed or crippled because they cannot form new exoskeletons and have a difficult time trying to shed themselves of their older, harder and undersized existing exoskeleton. You can often see adult cockroaches whose wings are misshapen or seem to be curling up. These roaches have been exposed to Gentrol and will not survive but for a short period of time."]
- Biological control - pathogens: The type of pathogen matters a great deal. Many viruses, for example, don't appear to inflict substantial suffering. However, various fungi appear to work rather slowly and erode the capacity of the insect. [Brian adds: As an example, the Bt bacterium produces toxins that erode an insect's gut and allow the insect to be overtaken by spores and bacteria over the course of several days.]
- Biological control - parasites: As with pathogens, there are many different parasites. However, it does not appear that death is quick and the quality of life appears to slowly erode. It has been noted, however, that some parasitized insects appear to act normally for much of the period of parasitization.
These are really brainstormed rankings and I'd be very open to refutation of my simplistic rationales.
As for moving the discussion into a wider venue, I can offer a few ideas. It might make sense to begin with a symposium as part of a national meeting. Perhaps the Entomological Society of America would be an interesting venue. Or you might go with a more philosophical setting for the discussion. There are also some organizations that fund/host workshops -- and I can imagine that a 1-week meeting to gather people together to hash out ideas, argue about positions, and exchange perspectives could be extremely exciting. Some journals are open to proposals for "special issues" (Psyche and Journal of Agricultural and Environmental Ethics come to mind), and you might also approach some academic publishers with this concept (this would be particularly viable following a symposium or workshop).
In terms of taking the concept into the realm of application, I would think that the Human[e] Society might be a fine organization. The concept of human[e] pest control/management is very intriguing. Of course, most people won't put a great deal of energy or thought into the matter. However, if there were alternatives that were no more (or even less) expensive AND more humane, then it could well matter to many people. In the best of all worlds, the Humane Society might provide a scoring or ranking system for methods and products (and even provide some explicit endorsement for consumers). The Freedom Foods label through the RSPCA would be one such model (perhaps insects could even be incorporated into the considerations for producers who seek this label). I suspect that some of the "what to do?" possibilities might make a most interesting session in a symposium or workshop.
As a follow-up, Jeff added:
As for the Human[e] Society or ESA, you don't come across as crazy -- just unusually curious and concerned about a phenomenon that matters to few people (at present). You could frame the issue not as: "How do we stop all the needless suffering of insects at the hands of cruel and clueless humans?" but along these lines: "What if insects can feel pain -- how would this change our pest management and other practices?" or "What is the current thinking on insect pain and what does this mean for laboratory, agricultural and other practices?" or "We are legitimately concerned about how we kill pestiferous rodents and birds -- should we extend our ethics to invertebrate pests?" or "If you could kill an insect instantly or slowly, which would you choose -- and what does this tell us about our moral duties?" or "Do we have ethical obligations to insects different than our duties to plants?" or "What does modern science reveal about the sentience and suffering of insects?" You see, posing an initiative, symposium or workshop in the form of a question draws people in and opens the door to dialogue. One approach would be to submit a poster presentation to ESA and then visit with people who come by, provide handouts that people can take away when you're not around so that they contact you, or post a "contact me" list on the poster for people to put their email addresses.
Does insecticide use in general increase or decrease insect suffering?
Reasons to think insecticide use is net good:
- Insecticide-sprayed fields may have lower populations of pest and non-pest bugs than organic fields, which means less wild-bug suffering, as well as fewer bugs injured during harvesting. In support of this trend, I anecdotally tend to find more bugs in organic vegetables bought from the store than in insecticide-sprayed vegetables. However, according to one meta-analysis, insecticide-sprayed fields did not have lower prey-insect densities than organic fields. But insecticide-sprayed fields did fortunately have lower populations of predator insects, soil organisms, and birds.
- Insecticides may kill nascent bug populations before they get huge, which might mean many fewer deaths than if the populations got huge and then the bugs died naturally.
- Ordinarily, killing bugs seems bad if other insects would just take the place of those killed, because killing animals prematurely in a population of a fixed size just increases the number of painful deaths per unit time. But there's not a saturated insect carrying capacity supported by crop food, because if insects don't eat crop food, it's not other insects that eat it but instead people, cows, bacteria, etc. (except for some scraps/waste).a
- In cases where crop cultivation increases primary productivity relative to counterfactual land, insecticide use makes farming more efficient and therefore implies less land use, thereby reducing suffering.
Reasons to think insecticide use is net bad:
- Killing tons of bugs obviously causes huge amounts of direct suffering, and death by insecticides is probably painful.
- Insect pests can reduce plant productivity. For example: "Plants exhibiting aphid damage can have a variety of symptoms, such as decreased growth rates, mottled leaves, yellowing, stunted growth, curled leaves, browning, wilting, low yields and death. The removal of sap creates a lack of vigour in the plant, and aphid saliva is toxic to plants." In a simplified model where bug suffering is directly proportional to worldwide plant productivity, reducing crop productivity always reduces insect suffering.
- In some cases, insecticides might increase target insect populations by destroying predators. For example, spraying of rice crops may kill predators that would have eaten pest-insect eggs, which allows more pest insects to hatch. Other mechanisms of post-insecticide pest resurgence may "include reduced competition with other herbivores, changes in pest behavior, altered host-plant nutrition, increased attractiveness of the plant host, or direct stimulation of the pesticide on the insect, factors that may operate singly or in tandem to give additive of synergistic effects (Hardin et al. 1995; Cohen 2006). Experiments do indeed demonstrate that hormesis could be an alternate or additional mechanism contributing to the pest resurgence phenomenon." But it seems doubtful that insecticides usually increase pest-insect populations overall in the short run, since if they did, people would stop using them. One meta-analysis that found about equal prey-insect populations on organic vs. insecticide-sprayed fields.
- If a bug species develops insecticide resistanceb, its populations may not be lowered as much, so more of those bugs will be born and suffer. But if insects are resistant, the painful effects of insecticides on them are lower than if they're not resistant. Moreover, spraying insecticides would still generally lower non-target bug populations, which is plausibly good. Also, the more pests are resistant, the more pesticides need to be sprayed, which may mean more total (target + nontarget) insect deaths, not fewer. As one paper notes, pest "resurgences could not only result in increased crop/commodity damage, but could lead to additional pesticide treatments, potentially exacerbating non-target impacts, insecticide resistance development and environmental contamination."
- Insecticides might increase the number of offspring per femalec, which means more insects die young even given a constant adult population size.
The upshot of this debate is unclear.
This article says "Scientists cite many factors in the fall-off of the world’s insect populations, but chief among them are the ubiquitous use of pesticides, the spread of monoculture crops such as corn and soybeans, urbanization, and habitat destruction." But did these findings of insect decline count soil invertebrates? One would expect that pesticide use would decrease aboveground insect populations but might increase belowground populations because more of the crop residue (stalks, leaves, etc.) would be left over to be eaten by detritivores.
If you think bacteria and other detritivores suffer about equally per unit of energy expenditure as insects, then you may be more worried about insecticides, since the main argument why insecticides might be good is that they may reduce the number of insects eating plants and thereby increase the number of less sentient microorganisms eating plant detritus. But if microorganisms matter equally per unit of energy consumed as insects, then an insecticide-induced shift from insects to microorganisms wouldn't reduce suffering, while killing insects prematurely would increase the number of painful deaths per unit time. That said, insecticides may also affect the total amount of plant food available to eat -- either by increasing primary productivity (since with insecticide spraying, fewer insects are eating plant leaves and inhibiting plant growth) or by decreasing primary productivity (insecticides kill soil organisms and thereby reduce nutrient cycling).
Does organic farming cause more or less insect suffering than conventional?
It's crucial to note that the choice between conventional vs. organic foods is more than the difference between insecticides or not.
Other reasons besides insecticides why organic food might be worse for insects than conventional:
- Organic farms might have more long-run primary productivity (and hence suffering by consumers of that productivity) because they don't don't degrade soil health as much.
- Organic farms also don't use synthetic herbicides, which may mean somewhat more weeds and hence somewhat more total biomass per hectare. One meta-analysis reports: "Weeds were more common in organic systems." According to another paper: "In many cases, [organic farms] will not completely eliminate all weeds." Still, commercial organic farms don't have huge numbers of weeds due to using various non-herbicide control strategies.
- Organic farms may have more nutrient cycling, i.e., faster turnover of nutrients through organisms. Insofar as nutrients are limiting factors for utilizing solar energy, more nutrient cycling may increase primary productivity and hence secondary productivity.
- Organic farms still may use painful pesticides like conventional farms do -- just non-synthetic pesticides. In fact, organic pesticides like Bt might be more painful (though this isn't clear). Another possible pest-control technique is flaming: "The brief but intense heat is enough to burn the insects antennaes and legs." When organic farms are managed properly, fewer pesticides are needed than on conventional farms, but this is often because organic farms have more instances of painful predation/parasitism on pest insects. That said, some organic pest-control methods like crop rotation are relatively humane.
- Organic farms might(?) use cover crops and no-till farming more than conventional farms. Cover crops may increase primary productivity of land by allowing plants to grow even when food crops aren't being grown. And insofar as both of these practices increase soil fertility, that also probably enhances primary productivity of crops, which is bad. (One silver lining of no-till farming is that fewer bugs are painfully chopped up during the tilling process.)
- If organic farms cause more suffering than counterfactual wild plants, then because organic farms have lower yields per hectare than conventional, they displace more wild hectares, thereby increasing suffering.
Other reasons besides insecticides why organic food might be better for insects than conventional:
- Generally lower yields: "Organic farms produce around 80% that what the same size conventional farm produces16 (some studies place organic yields below 50% those of conventional farms!)."
- If organic farms cause less suffering than counterfactual wild plants, then because organic farms have lower yields per hectare than conventional, they displace more wild hectares, thereby decreasing suffering.
- If climate change is net bad for wild animals like insects (which isn't clear but might be true), then if organic farming contributes less to climate change (which is plausible but probably varies depending on the situation), then organic farming would be better on this dimension.
Why insecticides may be better than other control methods
There are several innovative control techniques that don't require insecticides, including
- Sterile insect technique (SIT): Releasing sterile males to reduce subsequent populations
- Mass trapping: Using attractants to draw insects to an area where they are caught and eventually die
- Mating disruption: Spreading synthetic pheromones to lure males away from actual females, thereby reducing future populations.
These methods are called "inversely density-dependent" because they work best for small populations.
If chemical insecticides are more painful than dying naturally (is this true?), then these methods would potentially achieve population reduction in a more humane way. In addition, these methods are all very friendly to the environment and human health, which makes them easier to sell to others. Because these methods don't entail active killing, they should be less objectionable even to many deontological animal activists.
My biggest concern with these methods is that because they target one pest at a time, they may not reduce insect populations across the board in the same way that broad-spectrum chemical insecticides do. Indeed, that these techniques preserve non-target species is seen as a benefit by advocates, but it's a cost in terms of animal welfare if, as seems somewhat more likely than not, insecticides prevent net insect suffering by substantially reducing populations.
SIT also requires breeding many new insects to be released, which means more suffering and death by raising more total insects. Initially I assumed that this would be outweighed by the longer-term population-reduction benefits, since if that weren't the case, SIT wouldn't be a very good population-control tool. However, now I'm less sure. This study says that in a region of Brazil treated with sterile males, the wild adult Aedes aegypti population was 418 individuals per hectare, while the SIT treatment released thousands of sterile males per hectare per week (see Fig. 2B and Fig. 3). Since only female mosquitoes suck blood, perhaps those carrying out SIT don't care if the total bug population increases as long as the female population decreases? Wikipedia's article on SIT doesn't dispute the idea that total insect populations may be increased by the procedure: "overwhelming numbers of sterile insects are released into the wild. The released insects are normally male, as the females cause the damage usually by laying eggs in the crop, or, in the case of mosquitoes, taking blood from humans."
These techniques seem net good if not replacing insecticides
Sometimes these control techniques may be introduced where previously no control was used, such as for malaria or other disease prevention. In this case, it's probably net good to use them because they have some population-reduction effect. Still, my main concern with interventions that focus on animal rather than plant populations is that, because they're not eliminating the plant energy that feeds the animals, they may just shift the suffering to other organisms. However, insofar as some targets like mosquitoes feed on animals rather than plants, this is less of an issue.
One of the reasons that pest control on crop fields may be good is that it decreases the fraction of plant biomass eaten by bugs, leaving more of the plant biomass to be eaten by humans or livestock (who suffer less per kg of biomass eaten). Insofar as non-insecticide pest control reduces bug populations on crop fields relative to what would otherwise be the case, the corresponding reduction in the fraction of crop biomass eaten by bugs seems good. Given that "Herbivorous insects are said to be responsible for destroying one fifth of the world's total crop production annually", improvements in insect control that are more effective than insecticides or act where insecticides currently don't are plausibly welcome. (Of course, increasing the effectiveness of insect control also changes the number of hectares of land that need to be farmed, which should also be factored into a full analysis.)
Promoting humane insecticides has risk of being misinterpreted
Usually when I mention the possibility of humane insecticides without sufficient explanation, people assume, "Oh, yes, insecticides are really bad. We should try to reduce their use." As I endeavored to stress in the opening of this piece, this may in fact not be accurate. The net impact of insecticides is not clear, but it seems plausible that insecticides reduce more suffering than they cause. Even though we could reduce net suffering with more humane insecticides, I'm concerned that many people would not understand that insecticides may not be net bad and would therefore draw the wrong policy conclusions. One reason for this is that most advocates who discuss insecticides at all are always trying to reduce their use wholesale, and few people think that crop insecticides might be net good except for farmer profits. This is a risk that any humane-insecticides campaign faces, and I think this concern should be taken seriously. Perhaps one could market-test messages to find ways to convey the point that wanting more humane insecticides is not just a step towards wanting no insecticides.
IPM may be bad
Integrated pest management (IPM) refers to a class of creative pest-control strategies that include but also go beyond insecticide use. While some IPM techniques are indeed humane relative to insecticides, some -- such as biological control -- are plausibly more painful. Moreover, insofar as IPM reduces insecticide use, it increases populations of non-target bugs. In broad terms, IPM is a less extreme version of organic pest control, which is plausibly net bad relative to insecticides. Identifying which specific components of IPM are positive for insects is a worthwhile task, but I'd be concerned about promoting IPM in a wholesale manner.
I think the most clear way to make insecticides more humane is to find chemical control methods that are equally lethal but kill in a less painful manner. That way effects on non-target species would be held constant. Maybe a next step in this direction would be to study how various chemical insecticides work and which ones kill more quickly and/or in ways that seem less likely to cause severe pain. One reference point could include how painful different insecticides are in humans, though obviously we couldn't take that at face value when translating to bugs. We could also contact people who design insecticides to see if they have ideas for less painful killing mechanisms.
Genetically modified Bt crops are plausibly bad
Although some studies dispute this, genetically modified Bt cotton probably reduces overall pesticide use. For example: "A 2012 Chinese study concluded that Bt cotton halved the use of pesticides and doubled the level of ladybirds, lacewings and spiders." This is probably bad because
- it seems that non-target bug populations generally increase
- Bt toxicity is plausibly one of the more painful ways to kill bugs.
In the case of corn, Figure 2 of this page shows a dramatic anticorrelation between adoption of Bt corn and insecticide use. Likewise, this anti-GMO study affirms that Bt crops reduce insecticide use. (On the other hand, herbicide-resistant crops probably increase herbicide use, which may reduce net wild-animal populations. So the sign of genetical modification varies from situation to situation.)
This article reports on a study which found that, sadly, "there's no evidence that GMOs have reduced the amount of wild plant and insect life on farms."
Maybe in developing countries, if people don't use any pesticides now, then Bt crops would increase "insecticide" use (counting Bt in the plant itself as an insecticide) relative to the counterfactual?
Is it good or bad to kill non-target bugs?
Above I suggested that broad-spectrum insecticides have the benefit of killing non-target bugs, while more targeted control measures don't. But is it good to kill non-target bugs?
The main argument why it might be good to kill pest bugs was that the food the pest bugs would have eaten would otherwise be eaten by humans, cows, and other non-insect organisms, which means that killing pest bugs doesn't just leave the food available to increase populations of some other bugs later.
However, non-target bugs weren't eating the crops in the first place (or else they would have been considered pests). So the above point doesn't apply in their case. Maybe the food they would have eaten will just be eaten by someone else? So killing them doesn't actually reduce future non-target bug populations and might only increase total non-target bug deaths?
One reason to think that killing non-target organisms does reduce total bug populations is that some non-target organisms contribute to nutrient cycling and soil fertility, whereas soil sprayed with broad-spectrum insecticides tends to be more lifeless and stagnant. So by reducing soil fertility, insecticides may reduce the rate at which new non-target bugs can be born. This video shows the ways in which soil organisms increase primary productivity of crop fields, although some effects of soil organisms, like suppressing weed growth, might reduce primary productivity.
I don't know which side of this debate is stronger, and I'd be interested to see more research.
Brady (1974) reports regarding fumigants (p. 559):
These compounds have a more drastic effect on both the soil fauna and flora than do other pesticides. For example, 99 percent of the microarthropod population is usually killed by the fumigants DD and vapam [the original text misspells this as "vampam"], and it takes as long as 2 years for the population to recover. [...] Also, fumigation reduces the number of species of both flora and fauna especially if the treatment is repeated, as is often the case where nematode control is attempted. At the same time, the total number of bacteria is frequently much greater following fumigation than before. This is probably due to the relative absence of competitors and predators following fumigation.
This passage is interesting for two reasons:
- It confirms that a sufficiently thorough decimation of invertebrate populations can prevent invertebrate populations from rebounding for some time, although I wonder if this effect is less pronounced aboveground where migration is easier? And maybe less thorough killing of soil organisms by non-fumigant insecticides would lead to a much faster population rebound?
- The discussion of bacteria jibes with the idea that bacteria can to some degree take the place of invertebrate animals. (Although maybe the "competitors" that the passage discusses were mainly fungi, not invertebrates? I'm not sure.)
This piece has benefited from discussions with several people, including Jeffrey Lockwood and Carl Shulman.
"Humane Pesticides as the Most Marginally Effective Cause" by Jeff M. Jordan
- What about when insecticides kill non-pest bugs that wouldn't have eaten the crops? If the food those bugs would have eaten is instead eaten by bacteria/fungi, and if we care less about bacteria/fungi per unit of metabolism than about bugs, then reducing non-pest bug populations still seems like a net win. Or if the food that the killed bugs would have eaten won't be eaten by anyone else (which seems unlikely), then killing bugs at least slows down nutrient cycling, although if nutrients aren't a growth-limiting factor, maybe this benefit is small and is not worth the cost of painfully killing lots of bugs? (back)
- Here's an irrelevant side note about pesticide resistance. Environmentalists often and perhaps rightly decry the spread of environmental toxins, warning that they threaten life on Earth. Meanwhile, environmentalists also complain that insects rapidly develop resistance to pesticides, rendering them ineffective. This is an interesting juxtaposition of views, though I suppose it makes sense if you care most about the survival of complex organisms with very long lifespans and slow rates of evolution. (back)
- This article explains:
Insecticides may have an indirect effect on insect pests by reducing or increasing reproduction (e.g., number of eggs laid or offspring produced per female). For example, insecticide hormoligosis has been implicated in increasing the reproduction of several insect species including the green peach aphid (Myzus persicae). Green peach aphid females produce 20 to 30% more offspring when exposed to certain organophosphate insecticides compared to aphids that were not exposed to these insecticides. The increase in reproduction is likely a direct result of the action of the insecticides on the aphids.
Furthermore, spider mites may respond positively to insecticide applications. For example, foliar or drench applications of imidacloprid (Merit) increased the number of eggs laid by twospotted spider mite (Tetranychus urticae) females by 20 to 50%.