November 25, 2017

Pesticides create pests

Published in The Ecologist Vol. 10 No. 3, March 1980.


Shell chemicals currently run an advertisement which states that 30 percent of the world’s crops is consumed by pests. The implication is clear: more and more pesticides must be bought from Shell to spray over the world’s crops in order to make more food available for the starving millions. If it could be shown that the millions of tons of pesticides that have been released into our environment in the last 30 years had actually had some effect in reducing pest depredations, then this would, indeed, be the correct implication.

The opposite, of course, is true. According to the National Academy of Sciences, pest damage in the US has increased from an estimated $8.4 billion (31:4 percent of the total crop) in the period between 1940 and 1950, to an estimated $9.9 billion (33.6 percent of the total crop) in the decade between 1951 and 1961.

Figures derived from the US Environmental Protection Agency (EPA) tell the same story. In spite of the fact that farmers in the USA today use 2.265 tons of pesticides – which is 12 times more than they did 30 years ago, the proportion of the crops lost before harvest has almost doubled. [1]

The Shell advertisement, rather than make out a case for using more pesticides, in fact, simply illustrates the total failure of pesticides to make any impact whatsoever on world pest depredations. Let us look into this a little more closely.

It is in the tropics that the counter-productiveness of chemical pesticides is most apparent. The reason is that the tropical climate favours the development of great ecological diversity. Thus, whereas a forest in a temperate area may contain no more than a few species of trees per hectare, one hectare of tropical rain forest can contain anything between 60 and 100 different tree species, together with thousands of other plants, mammals and reptiles.

There is also a correspondingly vast diversity of insects which leads to a high incidence of disease among livestock and which, as Biswas points out, is one of the reasons why beef and veal production in the tropics is more than five times lower than in temperate areas. [2]

A further factor is that in tropical countries there are no winter frosts to reduce pest populations as in temperate areas and pests are thereby assured of a permanent habitat.

In these conditions, pest-control is correspondingly more difficult. Indeed while pesticides might be able to control a limited number of target species, to expect them to control the vast numbers of potential pests harboured by a tropical ecosystem is simply asking too much. If a pesticide succeeds in reducing the population of a target species, it creates an empty niche, which is immediately filled by another form of life, one that may even be more harmful to the crops than was the former. Also since pesticides are increasingly non-specific, they must upset the particularly delicate system of checks and balances which previously prevented a population explosion in any one species – and in this way, create a pest outbreak.

Dr B. J. Wood has drawn up, in a local Malaysian agricultural journal, an extensive catalogue of the instances in which large scale crop spraying programmes have had to be abandoned because they were leading to an increase, rather than a decrease in plant losses. This is well demonstrated in the experience of cocoa growers.

Cocoa

In Sabah (North Borneo), cocoa plantations were established in clearings in a primary forest, in which saplings were commonly retained for shade. The plants were almost immediately attacked by borers, especially Endoclita hosei, the caterpillar ring-bark borer. Planters applied dieldrin, at first, with apparent success. However, this led subsequently to a proliferation of leaf-eating caterpillars, and spraying was increased, this time using other pesticides.

When, in consequence, still more pests of various groups appeared, the planters could find nothing better to do than to increase the amounts of pesticides. Finally, an outbreak of psychid bagworms caused total defoliation. The planters had now learnt their lesson. They drastically reduced spraying and shifted to more specific pesticides and the situation slowly came wider control.

In Ghana there have been similar experiences. Although the use of broad spectrum organosynthetic pesticides largely suppressed the cocoa pests that had been most harmful locally in the past, it also led to the destruction of the enemies of certain other pests, which were then able to proliferate. The pests involved were husk-mining caterpillars, cossid branch-borers and web-forming bark-ring caterpillars. The last two of these showed a clear infestation gradient – from high numbers in the sprayed areas to extremely low (normal) numbers one mile away.

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Rice

In Vietnam, Laos, Cambodia and Thailand the brown rice plant hopper Nilaparvata lugens is at present causing havoc with the rice crop. The insect sucks the plant’s juices and the rice dries up. Fields become brown, the damage is referred to as ‘hopper burn’. Attempts to control it with chemical pesticides has killed off its natural predators and have little effect on the pest itself. In any case pesticides are increasingly difficult to obtain as is the spray equipment for which spare parts are very scarce.

The result is widespread hunger. The government in Hanoi last year appealed for food relief for 1,700,000 people whose food supply had been affected by the pest outbreak. The New Scientist points out,

“The upsurge of this pest is particularly embarrassing to the international group of agricultural experts dedicated to insect control. For it appears that certain fundamental changes in agricultural practices. . . to make the most of the new high-yield rice varieties may be responsible.” [3]

Indeed the brown rice plant hopper was never as destructive as this in the past, it is only in the last ten years that its numbers have increased so dramatically. The reason is that farmers now plant three not two rice crops a year so the plant hopper has food all the year round. Also, irrigation ditches are never drained so the wholly mobile plant hopper, uses these ‘water highways’ to travel from field to field. Nor do they have to fear their traditional enemies, as increased use of pesticides has killed them off.

In addition it is very difficult to get at the plant hoppers with pesticides because the new rice varieties developed by the famed International Rice Institute in Manilla are leafier and provide more top cover and protection. Nor have they developed any resistance against this pest as did the traditional varieties once grown in these areas and efforts to breed resistance artificially into the new variety have been unsuccessful.

These few examples are in no way exceptional. Other efforts to eliminate the pests that devastate agriculture in the Third World, have, on the whole, been no more successful. Consider how vain have been all efforts to stamp out locusts and weaver-birds. They have never been more populous than they are today and the devastation they cause has never been greater; while the anopheles mosquito that transmits malaria and the snail – vector of schistosomiasis, are proliferating as never before, in spite of the thousands of millions of dollars that have been spent on frenzied efforts to eradicate them.

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Pest control in temperate areas

Though pesticides should be more effective in temperate areas where there are far less potential pests to control, their use in these areas has not been very much more successful. In the US, a large proportion of all pesticides, in the last decades, has been used against a relatively small number of pests, in particular against the spruce budworm, the douglas fir tussock moth, the gypsy moth, the fire ant, the boll weevil and a few other pests of cotton.

I showed in a previous article just how counter-productive have been the massive spraying programmes undertaken against the first three of these pests. [4] In each case, as I noted, the main effect of the spraying programme was to perpetuate epidemics which, if left alone, would have died a natural death. Let us briefly consider the experience of attempts to eradicate the other major pests.

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The Fire Ant

The fire ant Solenopsis invicta was introduced into the south eastern states of the USA probably from South America between 1933 and 1945. It has a powerful sting and builds mounds which slightly interfere with agriculture. This has provided an excuse for vast spraying programmes using a pesticide called Mirex in a completely vain effort to eradicate it.

In 1967 a National Academy of Sciences Committee was set up to examine the feasibility of other spraying programmes. It concluded that the fire ant was not an important pest, that the eradication effort was unlikely to succeed and that limited local control measures would be adequate. However, the US Department of Agriculture completely ignored these recommendations and ordered more spraying. It was no more successful than the previous programmes. Recently it has been estimated that to eradicate the fire ant another $500 million would be required and even then success could not be guaranteed.

As George Allen, insect pathologist at the University of Florida writes, “the worst thing we ever did was to use the word eradicate. We couldn’t eradicate this thing with an atom bomb”. Yet if it is not eradicated, spraying will simply serve to select tougher and more resistant strains. Quite clearly, as Allen admits, “the thing people in this country have to learn is that they’re going to have to live with the fire ant”. [5]

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The Boll Weevil

One of the most serious agricultural pests that the US has to contend with is the boll weevil. It is said to cost cotton growers $200-300 million each year. In 1958, the cost of boll weevil depredations together with the cost of controlling it, are said to have amounted to $10 billion. Some 25 percent of all agricultural insecticides in the US are used for boll weevil ‘control’.

What makes the boll weevil particularly invulnerable is its ability to survive on plants other than commercially-grown cotton; in particular on a variety of wild cotton and on the ornamental plant Althea. If the boll weevil is to be eradicated then these plants must go too but this is by no means easy. Advocates of continued spraying admit today that it could cost as much as $650 million to eradicate the boll weevil and it is increasingly clear that even such expenditure would have very little effect. [6]

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Theoretical considerations

It is interesting to note that simply on theoretical grounds, these programmes had to fail. One of the main reasons is that resistance to pesticides inevitably had to build up. The only way we could have prevented this would have been to repeal the law of natural selection which even ICI and Shell and the other giants of the agrochemical industry would have been incapable of doing.

Natural selection assures that the fittest survive. The fittest are those that are best adapted to the environment in which selection occurs. Pesticides totally modify the environment and those that were previously the fittest no longer are, in the changed conditions. Those that have become the fittest and will now become selected to the exclusion of all others, are those that have developed resistance to the pesticide used. What is more, resistance among insects, which often have a new generation every two weeks, builds up very quickly.

Already according to the United Nations Environment Programme’s (UNEP) “State of the Environment Report” [7] there are 364 arthropod pests which are now resistant to nine of the major groups of pesticides and these include

“major pests of major crops, such as the cotton boll worm, the boll weevil, the leaf worm of cotton, the rice stem borer and the brown plant hopper, the Colorado beetle of potatoes, spider mites of fruit and glass house crops and cut worms and weevils of cereals.” [8]

What is more, as Newsom points out,

“The heavier the pressure put on a species the more likely you are to bring about inherent resistance.” [9]

The more we spray, in fact, the more rapidly will resistance develop and resistance has actually doubled since 1965 and at the current rate, will have become generalised among major agricultural pests in but a few decades.

Once a pest develops resistance to a particular insecticide, the normal procedure is to switch to a new pesticide but this requires constantly developing new pesticides which the chemical industry is finding increasingly difficult to do. The costs of meeting toxicological and ecological standards are growing very rapidly. Let us not forget too, that to amortise the development costs, the pesticides must be saleable worldwide, not just in one country. In many countries, though not in the UK, controls on their use are increasing.

It is estimated today, that the cost of obtaining worldwide registration has increased at a rate of 30 percent per annum, and it is now supposed to cost £10 – 15 million to bring a new pesticide on to the market. Also, because of the rapid build up of resistance among pests, the pesticides may only be effective for a few years, nothing like enough to pay for development costs. Not surprisingly fewer and fewer new pesticides are being developed. According to WHO, no manufacturer submitted a new pesticide for testing in 1978, and this organisation is now cutting down its field staff involved in the testing of pesticides.

For these reason and there are others, it is but a question of time before pesticide use becomes fairly peripheral.

We will have been forced to use subtler means of dealing with agricultural pests. The crude blunderbuss approach of spraying crops with a witches brew of toxic chemicals is going to be ever less feasible. To quote Van den Bosch,

“the harsh reality of the situation is that we must live with pests – be they insects, mites, snails, worms, fungi, bacteria, viruses, epiphytic plants, allergens or weeds. Rarely do we eradicate them; the best we can do is to co-exist with them.”

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References

1. Lappe & Collins, Food First, Penguin Books.
2. Biswas, M. & A., Food, Climate and Man, Wiley & Son.
3. New Scientist 2 November 1978.
4. “The Future of Tree Diseases”, The Ecologist Nos. 4 & 5, July/August 1979.
5. US News and World Report, 17 Jan 1977.
6. Kevin P. Shea, “The Last Boll Weevil”. Environment Vol. 6 No. 5.
7. United Nations Environment Programme’s (UNEP), State of the Environment Report 5 June 1979.
8. Nature Vol. 279, 24 May 1979.
9. “Eradicating the Boll Weevil”, Science, 8 Feb 1973.
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