Tag Archives: insectides

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