One of the fundamental concepts of toxicology is that chemicals act at selective receptors and that such interactions result in phar macologic responses which, depending on dose, mayor may not result in toxicity. For us to understand how insecticides produce their toxic effects, we must first understand their molecular interactions with their target receptors. With this in mind, we organized a symposium which was given in conjunction with the XVII International Congress of Entomology in Hamburg on August 21, 1984. The goal of this symposium was to bring together researchers with a wide range of expertise who shared a common interest in the action of insecticides on the insect nervous system. It was decided to restrict the scope of the symposium so that selected topics could be discussed in greater depth. The volume which resulted from this symposium, -Membranes Receptors and Enzymes as Targets of Insecticidal Action-, details a number of bio chemical modes of action of insecticides on the insect nervous system. The volume is divided into two sections; the first dealing with the action of insecticides on the GABA-ch1oride channel complex. This section evolves from a discussion of the symptoms of cyclodiene toxicity presented by Dr. D. E. Woolley, to the structure-activity relationships and pharmacology of the channel complex and is concluded with the extremely interesting work of Dr. C. C. Wang on the action(s) of avermectin at this receptor.

Why are books written? Since I have read many works by my colleagues with admiration, this question has always intrigued me. Further, writing a book takes a good deal of time and effort, and I had imagined that I would never undertake such a demanding task. A few unexpected events and circumstances have changed my mind. The first was the pleasant experience of editing Environmental Toxicology of Pesticides with Drs. Mallory Boush and Tomomasa Misato. This fine symposium volume occasioned many interesting responses, including a suggestion to prepare a more complete treatise on the grounds that such "proceedings" volumes, by their very nature, do not satisfactorily offer a complete and coherent description of the field, but cater chiefly to specialists. I myself prefer single-authored books for basic understanding of a scientific field. The second circumstance leading to the present volume was the avail ability of teaching notes from my course on the toxicology of insecticides. As the need to cultivate environmental awareness has increased, there has been a parallel increase in the enrolments of such courses both here and in other major institutions. Yet no comprehensive and up-to-date text has been available. The third factor which facilitated the effort was an especially pleasant sabbatical in Hawaii, where the availability of the excellent Hamilton Library at the University of Hawaii considerably eased my task."

When first developed, chlorinated pesticides such as DDT, dieldrin, and mirex were received with open arms, quickly becoming popular as effective, economic agents against pests. But evidence began to mount that residues of these chemicals remained in the environment, not breaking down, often appearing in plants and animals. By the late seventies many pesticides had achieved a terrible notoriety and were subsequently banned in a number of countries. Of tremendous concern, then, is the persistence of pesticides in the environment. The major thrust of research and development in the area of pesticides has properly been the creation of substances that are both effective and degradable. Yet in order to successfully promote the use of biodegradable pesticides, one must fully understand the mechanism of degradation, and it is to this vital subject that we address ourselves in the present volume. According to the Biodegradation Task Force, Safety of Chemicals Com mittee, Brussels (1978), biodegradation may be defined as the molecular degradation of an organic substance resulting from the complex action of living organisms. A substance is said to be biodegraded to an environmentally acceptable extent when environmentally undesirable properties are lost. Loss of some characteristic function or property of substance by biodegradation may be referred to as biological transformation."