2021年10月 / 马哥(Marlin)整理

15. Nature Fights Back / 大自然的反击

(部分节选 - 可能不完整)

The balance of nature is not the same today as in Pleistocene times, but it is still there: a complex, precise, and highly integrated system of relationships between living things which cannot safely be ignored any more than the law of gravity can be defied with impunity by a man perched on the edge of a cliff. The balance of nature is not a status quo; it is fluid, ever shifting, in a constant state of adjustment. Man, too, is part of this balance. Sometimes the balance is in his favor; sometimes—and all too often through his own activities—it is shifted to his disadvantage.

Two critically important facts have been overlooked in designing the modern insect control programs. The first is that the really effective control of insects is that applied by nature, not by man. Populations are kept in check by something the ecologists call the resistance of the environment, and this has been so since the first life was created. The amount of food available, conditions of weather and climate, the presence of competing or predatory species, all are critically important. “The greatest single factor in preventing insects from overwhelming the rest of the world is the internecine warfare which they carry out among themselves,” said the entomologist Robert Metcalf. Yet most of the chemicals now used kill all insects, our friends and enemies alike.

The second neglected fact is the truly explosive power of a species to reproduce once the resistance of the environment has been weakened. The fecundity of many forms of life is almost beyond our power to imagine, though now and then we have suggestive glimpses. I remember from student days a laboratory experiment that I watched with fascination. A small flask containing a simple mixture of nutrients in water was inoculated with a few paramecia—tiny, single-celled protozoans that can be found in almost any pond or ditch water. Within a few days the flask was cloudy with paramecia; in a week or so it was so full of them that they could have been scooped out with a spoon. Then came an astonishing thing. Each paramecium divided in two, and each of the two resulting cells divided again, and so on, until the flask was so crowded that food ran short and the end of the paramecium boom was in sight. This was an example of what could happen in other circumstances through the sheer biotic potential of a single-celled organism.

Suppose, for example, that a farmer sprays his fields with DDT. As the poison drifts down through the air or percolates through the ground, it is picked up by the insects and other organisms in the soil and water, or by the plants that grow there. The poisoned insects may die immediately; the plants may show signs of damage or may absorb the poison and pass it on in their tissues. But what about the unhatched eggs of the insects, or the larvae that have not yet emerged from their cocoons? And what about the parasites and predators that depend on the insects for food? They are all part of the complex web of life, and when one part is poisoned, the whole structure is weakened.

The effect of the poison on the parasites and predators may be even more serious than on the insects themselves. For example, many of the birds that eat insects are highly sensitive to DDT and other pesticides. When they feed on poisoned insects, the poison accumulates in their bodies, causing them to lay eggs with thin shells that break easily. As a result, the bird population declines, and with it the natural control of the insect population. In the same way, the predators that feed on the insects may also be killed off, leaving the insects free to multiply without restraint.

This is exactly what has happened in many parts of the world. In Ontario, for example, the spraying of DDT to control the spruce budworm had an unexpected result. The budworm population, which had been increasing steadily, suddenly exploded after the spraying, reaching levels that were far higher than before. The reason was that the spraying had killed off the parasites and predators that had been keeping the budworm in check, while the budworm itself had developed a resistance to the poison.

The same thing has happened with other insects. The spider mite, for example, was once a minor pest, kept in check by its natural enemies. But with the widespread use of DDT and other pesticides, the spider mite has become a major problem, attacking a wide variety of plants and causing serious damage. In some cases, the use of pesticides has actually created new pest problems by destroying the natural enemies of the insects.

It is not only the insects that are affected by the use of pesticides. The entire ecosystem is disrupted, with far-reaching consequences. The plants that are sprayed may be damaged or killed, reducing the food supply for other organisms. The soil may be contaminated, affecting the growth of plants and the activity of soil organisms. The water may be polluted, harming fish and other aquatic life. And the birds and other animals that depend on the insects for food may starve or be poisoned.

In short, the use of pesticides is a double-edged sword. While it may seem to offer a quick and easy solution to the problem of insect control, it can also have serious and unexpected consequences. We are tampering with the balance of nature, and we do so at our peril. If we continue to use pesticides without regard for their effects on the environment, we may find ourselves facing even greater problems in the future.

As Rachel Carson pointed out, “We have put poisonous and biologically potent chemicals indiscriminately into the hands of persons largely or wholly ignorant of their potentials for harm. We have subjected enormous numbers of people to contact with these poisons, without their consent and often without their knowledge. … I contend, furthermore, that we have allowed these chemicals to be used with little or no advance investigation of their effect on soil, water, wildlife, and man himself. Future generations are unlikely to condone our lack of prudent concern for the integrity of the natural world that supports all life.”

We need to take a more careful and responsible approach to insect control. We need to look for ways to work with nature, rather than against it, using methods that are safe for the environment and for human health. We need to recognize that the balance of nature is a precious and fragile thing, and that we are all part of it. Only by respecting and protecting the natural world can we hope to ensure a healthy and sustainable future for ourselves and for generations to come.