All have their worth and each contributes to the worth of the others.

J.R.R. Tolkien, The Silmarillion

When you try to study something in isolation, you find it hooked to everything else.

John Muir

It becomes necessary in any active scientific discipline to sit back every few years and take stock of the “state of the art.” The time arrives to review recent progress, inspire new ideas, and propose critical and novel lines of research.

In 1963, Yoshinori (“Joe”) Tanada laid the foundation for the current book with his chapter “Epizootiology of Infectious Diseases” in E.A. Steinhaus' Insect Pathology: An Advanced Treatise, a two-volume reference that defined the scope of invertebrate pathology. By 1987, after almost a quarter-century, the time had come for more than just a review of the “state of the art.” Fuxa and Tanada formalized the new scientific discipline in their edited monograph, Epizootiology of Insect Diseases, organizing an emerging field of study by establishing its components, definitions, types of studies, and research methods.

Another 30 years have passed, and that time has come again. Much has happened since 1987 – science never stands still. New methods have opened doors unheard of in the 1980s, most notably in molecular biology. Detection and characterization of strands of DNA, RNA, and transposable genetic elements create almost unlimited research opportunities in ecology. New diseases have emerged, such as the mysterious colony collapse disorder of the honeybee, which has raised concern throughout much of the world. Previously characterized diseases have erupted again in devastating epizootics, notably MSX disease (Haplosporidium nelsoni) and dermo disease (Perkinsus marinus) in populations of oysters. New relationships have opened eyes – who would have thought that microsporidia are highly evolved fungi, not primitive protozoans that evolved before the advent of mitochondria? New concepts have arisen for invertebrate pathogens, contributing to theory in general ecology and host–pathogen coevolution.

Thus, we arrive at this new book. The reader, however, might ask, why Ecology of Invertebrate Diseases rather than Epizootiology of Insect Diseases? A definition of epizootiology borrowed from the 1987 volume, “the science of causes and forms of the mass phenomena of disease at all levels of intensity in a host population,” allows for study of the total environment, including the host and pathogen populations, even a pathogen's environment inside its host. Epizootiology in turn is a subset of ecology, which was defined by H.G. Andrewartha as “the scientific study of the distribution and abundance of organisms,” a definition that has evolved to embrace concepts of “population” and “ecosystem.”

Simpler may be better. Epizootiology is the study of animal disease at the population level. It fits well into a broader mold of ecology, as outlined by Tolkien and Muir, if they may be paraphrased, that everything is “connected to everything else” and “contributes to the worth of the others.” Perhaps these two authors were not trying to define ecology, but they might just as well have been.

The editors of this book realized that the “state of the science” has exceeded the scope of the 1987 monograph, thereby creating a multitude of opportunities to discuss new concepts and types of studies, not to mention the myriad of non-insect hosts of infectious disease. Even in a new volume, however, old questions arise, especially, why study ecology of pathogens and their hosts?

First and foremost, parasites are not just dirty little things living a disgusting lifestyle. They are highly evolved organisms – or near-organisms – as intricate and unique as any creature on the planet. They contribute to all, whether by culling the weak or by transporting bits of DNA, in relationships with their hosts ranging from near-benign to something out of a horror film. The reader who delves into this book will see the “worth” in these fascinating little creatures, whether prokaryotic, eukaryotic, or viral.

And, of course, invertebrate pathogens certainly are “hooked to everything” abiotic and biotic, even to humans, a web of life and environment and planet earth. Many such interactions almost defy belief, for that is life.

Science also is called upon to provide tangible benefit. The historical advantages of studying invertebrate diseases remain as important as ever – enhancing disease in pestiferous organisms and preventing disease in invertebrates useful to humans. Pathogens, even viruses, function as parasites with population-level and ecological characteristics, parasites that must be suppressed in populations of beneficial organisms or conserved or enhanced if they are to succeed in pest management. Critics, however, might say that such “germ warfare” against pests is passé, that we now have genetically modified crops, recombinant mosquitoes, and on and on. Perhaps. However, the biopesticide market, which is based on mass production of invertebrate pathogens, continues to grow. Moreover, nothing works in isolation. For example, understanding the dynamics of insect population resistance to disease facilitated management of resistance in widespread use of crops incorporating toxin genes and environmental risk assessment contributed to a safe, first release of a recombinant baculovirus.

Diseases of invertebrate hosts, many of them easy to culture, with their tiny sizes and short generation times, also serve as model systems giving insight into disease ecology in higher organisms – for example, contributions of pathogen reproductive rate, transmission, and virulence to epizootics.

So much for the “What?” and the “Why?” of this book – how about the “Who?” Many decisions were made in compiling this monograph, not the least of which is, where does one stop if everything is “hooked to everything else”? Researchers will find themselves fortunate in this volume's scientific writers, fortunate because they will recognize the names of the editors and authors, all outstanding pathologists, ecologists, or epizootiologists. Readers will appreciate as they peruse this book that, much like Tolkien's world, every author has indeed “contributed to the worth of the others.”

James R. Fuxa
Louisiana State University (Retired)