Pesticide use & Rachel Carson’s Silent Spring – part 1

On reading Rachel Carson’s Silent Spring, several timeless conclusions can be drawn about pesticide (insecticides or herbicides) use. Carson, intelligently, did not argue against the use of pesticides point blank, but pointed out the limits of relying solely on chemicals to control pests without considering their wider effects on the balances in nature and human health. Due to this narrow focus, the use of chemical pesticides have sometimes not only been futile, but have exacerbated pest problems.

I’ve tried to keep most of the points general, because Silent Spring mostly addressed DDT pesticides. DDT pesticides are no longer used today except for treating disease carriers, known as vectors (so it is still used on mosquito nets in an attempt to stave off malaria, for example). That’s why some of her points directly aimed at DDT are not included. Originally I intended for this to be one post, but it ended up being a little long, so I’m going to do this in sections. If you know more than me and I’ve written something stupid, let me know. I admit I’m not a scientist, although I appreciate that Carson wrote very accessibly, which is what made this book so important. Points are ordered in chapters, starting from the first to the last.

The obligation to endure

Insect problems have arisen due to the intensification of agriculture that devotes many acres to a single crop. Prior to such intensification, serious insect problems were rarely encountered by farmers. Single crop farming may be economically beneficial to a few, although it does not “take advantage of the principles by which nature works,” as we will see. Logically though, an insect that lives on wheat for example can increase its numbers far more easily if it’s in a field full of wheat, as compared to a field with other plants it is not interested in.

Another reason for the new insect problems is the ever increasing movements of people, who introduce new insects to new areas, which lack the predators that control it in its original habitat.

While there are many specialists working on the problem, many fail to see the it from a holistic perspective, and this myopic view of nature is continued at our own peril.

Surface waters and underground seas

Chemicals inevitably find their way into waterways, where a “mixing” of otherwise “safe” chemicals can create new toxic chemicals that chemists would not deem suitable for human or animal consumption.

Earth’s green mantle

The destroying of various kinds of plants labelled as “weeds” using chemical treatments also has consequences for all other creatures and plants that have a relationship with that plant. For example, animals that depend on the target plant for food, other plants that flourish alongside the target plant, and the particular soil and climate of the region that the target plant flourishes in as a result of many years of evolution – all these are affected when the target plant is suddenly removed. The new plants which take their place (usually crops useful to humans) are often not well adapted to the particular climate or soil, thus they will require further additions of chemicals (either to remove subsequent insect, animal or plant pests, or to add the necessary nutrients to the soil).

Some imported insects, whose food source consists of specific kinds of weed, have been used to control some weeds.

Needless havoc

Insecticides affect other animals that eat the poisoned insects, such as birds. Thus, while certain chemicals may be established safe for some kinds of insects, the effects on the wider food chain may not be known until it is too late.

Alternatives such as introduction of bacterial, fungal or viral infections that only affect the target species are not only more effective at controlling the populations of pests, they have fewer side effects for predatory animals and often only need to be used once rather than requiring re-spraying. Introduction of predatory animals can also be cost effective. For example, if an introduced pest becomes a threat or nuisance, the importation of the pest’s natural predator in its country of origin and its introduction in the new location can be effective in controlling the original pest.

And no birds sing

Insecticides rendered as “safe” by chemical manufacturers are often tested on domesticated animals rather than wild animals, and the tests are done in labs. Thus, the effect on wider species may not be known unless field tests are conducted or the chemical is applied in a natural setting.

Many DDT-based insecticides cannot be removed by rainwater, thus, their effects last multiple seasons.

Sprays can be economically inefficient for several reasons:

  1. Due to the unintentional poisoning of various other animals through the food chain, natural predators of the target pest can be eliminated, thus destroying the natural limits on the pests’ spread. Furthermore, even if some animals do not die due to ingestion or exposure to the chemicals, their reproducing capacities or other functions crucial to their survival, are negatively affected.
  2. Due to the above phenomenon, multiple sprayings are required, as natural controls on insect populations are adversely affected

Often the widespread need for chemical sprays to control pests that affect a particular kind of plant arise from the lack of diversity of the plants. It is noted that having a variety and diversity of plants in a particular area reduces the likelihood of pests from causing widespread damage and thus the need for major spraying, as the severity of damage is not as wide.



Filed under Ecology

3 responses to “Pesticide use & Rachel Carson’s Silent Spring – part 1

  1. Interesting perspective of Ms. Carsons work. She too had unintended consequences or perhaps the were intended all along. I really don’t mind varying research work when it is put out in a way that lets truth speak for itself or at least offers an opinion but is approached much as in the way you approached your article. Ms. Carson however had an obvious agenda driven motive and her facts have been discredited for quite some time.

    • Clearly, Rachel Carson had an agenda when writing that book, but probably no more of an agenda than the chemical companies she was railing against. Interestingly, many of her critics have clearly not read the book, for example this article in Capitalism Magazine notes that due to Carson’s book, DDT has been banned worldwide and this has caused the unnecessary deaths of many in the developing world suffering from malaria. This sort of critique is noted in the Wiki article about DDT which also states that DDT is NOT banned in the area of vector controls (so it can actually be used in mosquito nets, because mosquitoes are a vector, or carrier, of malaria). Further, Carson addresses the issue of mosquitoes and malaria in the book, which the writer seems to have missed. She notes that due to the resistance that can be built up by mosquitoes, chemical forms of control for vectors (disease carrying pests) have an obvious limitation. Even if you don’t accept the particular studies that she has cited, anyone who has a basic understanding of biology and evolution can see that resistance is going to be a problem with purely chemical forms of pest/weed control (although practical evidence is also available). What is admirable is that she doesn’t just critique chemical controls, she offers alternatives, and she doesn’t state that using chemicals, even DDT, should be banned outright (although much of the critique of her book seems to assume that she argues this). While reading the book it was clear that not all the alternatives she offered would be perfect (there are, for instance, clear limitations to introducing target pest predators), however she does do a good job of pointing out the wider effects of chemical pest control, why we should care, and what else should at least be tried.

      Just to reiterate, the selections of currently relevant points I have made are just that – selections, in order to stimulate discussion. I don’t agree with everything she says, but I’ve tried to reserve my commentary and provide a summary.

  2. Pingback: Rachel Carson’s Silent Spring – Part 3 « Fix

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