The Interaction Of Human Engineers With Ecological Engineers The Case Of Pesticides

Although this chapter for the most part ignores the human engineers that play so central a role in this particular ecosystem, it would seem perhaps too parochial not to at least mention some ways in which dramatic engineering feats have interacted with the ecological engineering that is the basis of this chapter. Indeed, some of these interactions have been quite spectacular, in a negative sense. When engineers make bridges whose span characteristics are such that harmonic vibrations cause their eventual collapse, we note the complexity of some design problems and the need to understand that complexity so as to avoid the problems in the future. Since the spectacular failure of the Tacoma Narrows Bridge in 1940, engineers take into account the subtle, but critical, aspects of bridge design, in particular the probability of harmonic coherence of oscillations causing expanding amplitudes. Human ecosystem engineers need to study their own failures and correct them in a similar fashion.

Pesticide-based agriculture emerged from the problems of overproduction generated by the end of World War II (WWII). The new agriculture was even referred to as "chemical agriculture" in some propaganda pieces. Problems with this new technology were evident from the start, but received massive public attention only after the publication of Rachael Carson's Silent Spring in 1962, which documented the fact that the massive use of pesticides was having a dramatic negative effect on the environment. Previously there had been much popular commentary about the human health effects of pesticides, a concern shared even by the pesticide manufacturers. But Silent Spring was the first popular account of environmental consequences, contributing not only to concern about environmental poisons, but perhaps providing the main springboard for the entire subsequent environmental movement.

What Carson said is now well known. Pesticides kill not only the targets, but also many species that are not targeted. Pesticides may concentrate in the higher trophic levels, thus making non-lethal doses at lower trophic levels quite dangerous at higher levels. Pests develop resistance to pesticides. The poisonous effects of pesticides and their residues may persist for a long time in the environment. These were the basic themes of her book, all of which implicate the ecosystem engineering aspects of pesticide effects.

A classic example of how Carson's principles worked themselves out, and how humans and pests can ultimately engineer an environment so hostile that certain species are effectively eliminated, is the case of cotton in Nicaragua (Falcon 1971). The beginnings of the story are in the same post-WWII climate referred to earlier. Landowners in Nicaragua saw cotton, the crop with an effectively undisruptable world demand, as a great potential due to the basic environmental conditions on Nicaragua's Pacific seaboard. The only problem was the cotton boll weevil, long known as a devastating pest in all of the Americas. But with the enthusiasm of the new focus on pesticides, boll weevils were simply another enemy to be vanquished and DDT was the armament that would do the job. Cotton was widely planted and DDT was sprayed a couple of times during the cotton growth cycle. The boll weevils died and the planters got rich. Yet only 5 years after its introduction DDT began losing its effectiveness. Furthermore the boll weevil reached densities in which it was an even worse pest than it had been earlier, and a new pest, the pink bollworm, had become even more important. Furthermore, several other pests now represented a pest suite that the planters had to deal with. But again there was an armament to solve the problem, this time the pesticide Aldrin. It had to be sprayed multiple times but was effective against both boll weevils and bollworms, along with a few other pests that had become important. Still, things got progressively worse. By the 1980s planters were spraying a cocktail of several kinds of pesticides over 27 times per growing season, to control 15 persistent and 9 occasional pests. The background environment had become saturated with a diversity of pest species that, by interacting with humans through the now well-known pesticide treadmill (van den Bosch 1989), engineered what became an impossible environment for the species we call cotton. It effectively became extinct because of these associated environmental engineers.

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