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Out of Sight — A Nerve-Wrecking War on Eyesores

What is the hardest war mankind has ever fought?

Image by NguyenVanHuylonghung on Pixabay

There is no doubt that one of the biggest hassles for any farmer in the world is seeing relentless weeds smothering their seedlings and hungry bugs devouring their harvests like wildfire. An effective pesticide is therefore a near miraculous invention in the eyes of many farmers. It can save them time and energy, and most importantly, like a pair of polarized glasses, it keeps them from seeing certain “hassles”. This is why we humans are known to be visual animals i.e., we build our faith on what we see. However, something fishy is always lurking and hidden in sight, or in time as we shall see.

A “Nerve-Wrecking” History

What makes a pesticide “visibly” effective? Highly toxic and lethal across generations and to multiple kinds of pests. In other words, an ideal weapon would be a magic shotgun that does not give any pests a chance.

How would this play out for the eternal enemy of every farmer — the tiny herbivorous crawlies? There are countless ways to annihilate insects, but not all produce the same visual result. In order to see an immediate, visceral result, some chemists figured out that we can attack an insect’s nervous system to instantly incapacitate it. This is how the famous “organophosphate” pesticides were born.

These chemicals work by inhibiting the universal neuromuscular enzyme acetylcholinesterase, causing the overstimulation of nerves and their subsequent exhaustion. Moreover, they are very potent in the sense that they can be absorbed through all surfaces on an insect body, meaning that there is near zero chance of escaping unharmed. If that sounds like something out of a horror movie to you, you would be correct.

Little did farmers know that these “magical” potions had evolved (or co-evolved) from some of the deadliest chemical weapons i.e. nerve agents used in wars and genocides. Unsurprisingly, mammals including humans use the same acetylcholinesterase enzyme in our nervous systems (although it is a bit different chemically due to the long history of divergent evolution). Therefore, organophosphates can also kill humans in a similar manner as we do to the tiny insects. For instance, the infamous and highly lethal VX agent used in the Angolan Civil War and several other murders (including the assassination of Kim Jong Nam, Kim Jong Un’s half brother) is analogous to the pesticide “Parathion” structurally and chemically.

The chemical structure diagrams are adapted from Figure 1 in McCann, J. J., Pike, D. H., Brown, M. C., Crouse, D. T., Nanda, V., & Koder, R. L. (2022). Computational design of a sensitive, selective phase-changing sensor protein for the VX nerve agent. Science Advances, 8(27), under Creative Commons.

At low dosage and repeated exposure, organophosphates can cause a variety of cognitive deficits such as impaired short-term memory, information processing capability, shortened attention span and other symptoms such as blurred and dim vision, headache, numbness or tingling, insomnia, difficulty walking, and even abnormal heartbeats. At high dosage, of course, it will result in a painful convulsion and paralysis followed by death.

On the plus side, organophosphates are generally biodegradable (because the phosphate group and its ester bond are common in nature) and so are not likely to persist long to affect a wider spectrum of organisms and generations after. However, organophosphates are just the tip of an iceberg, there are many “careless” agrochemists who have developed less biodegradable nerve-attacking pesticides like the organochlorides (where the infamous DDT belongs). This has led to a series of misfortunes because they are relatively longer-lasting and their lipophilic nature even allows significant bioaccumulation which would affect a wide array of non-target organisms including humans. Despite widespread bans in most developed countries, the use of organochlorine pesticides has continued to rise, especially in developing countries.

Zero Chance to Live

Image by Aqua Mechanical on Flickr Creative Commons License

Being “visually” effective and “actually” effective in killing target pest populations are in fact two distinctly different concepts that most people, including farmers, have a hard time grasping. In the case of tiny insect pests, farmers typically feel their job is done when they witness little buzzing activity going on (hence “Silent Spring”). Therefore, a lot of farmers will over-spray insecticides to “cleanse” every spot on their farms and unsurprisingly, the majority (> 99%) of the pesticides are going to be taken up by non-target organisms. This way, you may be able to leave zero chance for the pesky pest to appear on your visual field, but the pest’s natural competitors and predators face the exact same fate. This results in increasingly severe pest infestations in their subsequent growth cycles. Farmers would then need to apply more and more pesticides to curb the increasingly uncontrollable infestation — an exponential rat race ensues.

There is a second reason why target specificity is so crucial. To illustrate this, we have to turn our focus to weeds, the true enemy that causes arguably more damage than all other pests combined.

Curbing weeds is no easy task. Since weeds usually comprise a mixture of different plant species, you often need a broad-spectrum or a mixture of herbicides to get things under control. What this means is that your timing and location of herbicide application need to be extremely careful in order to not destroy your own crop (the non-target that is also the breadwinner). Even if we use a selective weed killer, it often ends up that another more resistant weed will just take over, meaning that you may need to increase dosage and frequency or use another herbicide, putting your crops at a greater risk.

There was then one ingenious solution that completely overturned this conventional herbicide conundrum. With the advent of gene-editing technology, scientists have experimented with introducing genes into crops (e.g., soybean, corn, cotton) that confer strong resistance to broad-spectrum herbicides like glyphosate (now the most used herbicide ever). In this way, all the hassles to farmers are gone because the timing, location, application method, etc. become irrelevant, all you need is to spray whenever something other than your engineered resistant mono-crop rises above the ground (think of your crops wearing a “Nazi’s” armband as a simple identification to avoid being killed in a genocide). Again, the same scenario as insect pests — everything wiped clean and eyesore is relieved.

As good as it appears, a large farm managed this way could inflict a serious impact on the proper functioning of ecosystems e.g., host plants of beneficial insects and barriers to plant disease are destroyed, and nutrient cycling is hampered. Moreover, it has been reported that glyphosate and its metabolic product are found in most environmental samples in the US i.e. soil, water, sediment as well as in food in both the UK and US, with concentrations that are shown in animal models to cause significant hepatorenal damage and potentially other health defects including cancer , reproductive development impairment, as well as potential neurotoxicity.

As you can see, there is a recurring dichotomy between short-term visual results and actual long-term, wider benefits. Only one party is clearly winning all the time, and you can probably guess who that is.

A “Schrödinger’s” Future

Okay, by now you probably get how scary pesticides can be, but they still serve the function of controlling pests, which is pivotal to feeding the planet, right? While making a value judgment is not in the realm of science, it doesn’t harm to learn a few facts and science knowledge to fight information asymmetry.

Over the 40 years span from the early 1960s to the 2000s, global food production has doubled and land use in agriculture has increased by around 10%. However, pesticide use in the same span has increased by more than 15-fold. This means that on roughly the same size of land, we applied at least 15 times more pesticide to secure a 2-fold increase in food production made possible also by other factors such as the much higher use of nitrogen fertilizer (almost 7-fold increase), increased irrigation (1.7-fold) and improved crop genetics. In fact, a number of experts have already voiced against the myth that pesticides are necessary to feed the world. Another shocking fact is that crop damage attributable to pests has slightly increased compared to 50 years ago despite pesticide use has skyrocketed. This suggests that our crops are increasingly susceptible to pest attack and require more pesticide input per unit crop production due to our poor agroecosystem resilience management.

There is no feasible way to measure the precise damage pesticides have inflicted on us and the environment, let alone make a fair comparison to the benefit (crop protection) they have given us. However, while one can argue that saving even just one starving human life could be worth all the damage, it is important to realize that people at present and people in the future are at odds to some extent, mediated by slow ecological processes. Therefore, it is important not to allow the act of saving one life today to become nothing more than an excuse to maintain a status quo that has no future.

We are all guilty of squeezing every last one of those tiny pimples, or getting rid of those annoying spider webs in every hidden corner, all to attain a perfectly clean scenery to look at. Perhaps it is time to start asking ourselves: Do we have to go this far? Should everywhere look like the “American lawn”?

Perhaps the answer lies in those imperfectly slow, more labor-intensive organic methods of pest control. Even though they won’t give us that perfectly silent mime show, at least I find them more lively and beautiful.

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