Coevolution and Integrated Pest Management

Anne and Paul Ehrlich explain the role and importance of integrated pest management and coevolution, a term they coined.

| March/April 1978

Paul Ehrlich (Bing Professor of Population Studies and Professor of Biological Sciences, Stanford University) and Anne Ehrlich (Senior Research Associate, Department of Biological Sciences, Stanford) are familiar names to ecologists and environmentalists everywhere. As well they should be. Because it was Paul and Anne who — through their writing and research — gave special meaning to the words "population," "resources" and "environment" in the late 1960s. (They also coined the term coevolution and did a lot to make ecology the household word it is today.) But while most folks are aware of the Ehrlichs' popular writing in the areas of ecology and overpopulation (most of us — for instance — have read Paul's book The Population Bomb), far too few people have any idea of how deeply the Ehrlichs are involved in ecological research (research of the type that tends to be published only in technical journals and college textbooks). That's why it pleases us to be able to present on a regular basis the following semi-technical column by authors/ecologists/educators Anne and Paul Ehrlich. 

The Role of Coevolution in Nature

Until very recently, biologists seemed to think that plants just had to lie there and take it. Caterpillars chomped their leaves, aphids sucked their sap and cows and goats slaughtered them outright. Only occasionally did plants do anything — grow spines, for instance, in the case of cactuses — to protect themselves from the onslaught of herbivores (plant eaters).

In the last decade, however, this picture of "defenseless" plants has changed completely. Biologists now realize plants have an astonishing array of defenses — both mechanical and (especially) chemical — at their disposal. Plants — we now know — do protect themselves.

Our own involvement in this revolution of understanding began in 1964 when one of us (Paul) had a series of conversations over coffee with plant evolutionist Peter Raven. Paul had asked Peter about some seemingly strange choices of food-plants made by butterfly caterpillars. For example, closely related butterfly species ate apparently unrelated plants, but sometimes those plants — such as the ones of the citrus and carrot families fed upon by the caterpillars of certain swallowtail butterflies — contained similar chemicals. What began as casual conversations soon escalated to a ransacking of the extensive scientific literature on butterfly foods and plant chemistry.

In the course of this literature search, it became apparent that plants and butterflies had — over the centuries — been fighting a sort of evolutionary war. Certain poisonous "secondary" chemical compounds in the plants — it turned out — were nothing less than sophisticated weapons of chemical warfare. In turn to protect themselves, the butterflies had evolved tricks for avoiding or detoxifying (making harmless) these poisons. What's more, each new defense strategy evolved by the plants put pressure on the butterflies to evolve a new attack, and each new strategy of attack by the insects called for a reciprocal defensive response by the plant. Paul and Peter called this kind of point-counterpoint stepwise evolution involving more than one species " coevolution."

In many cases, coevolution has led to great specialization on the part of herbivores. The swallowtail butterflies, for example, are so adept at detoxifying one kind of chemical produced by their citrus- and carrot-family hosts that the chemical has actually become an attractant!  

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