Ecology of Invertebrate Diseases
Ecology of Invertebrate Diseases is a necessary and long overdue addition to the world literature on this vitally important subject. This volume belongs on the reference shelves of all those involved in the environmental sciences, genetics, microbiology, marine biology, immunology, epidemiology, fisheries and wildlife science, and related disciplines. ANN E. HAJEK, P H D, is a Professor in the Department of Entomology, Cornell University, Ithaca, New York, US. DAVID I. SHAPIRO-ILAN, P H D, is a Research Entomologist at USDA-ARS, Byron, Georgia, US.
Ecology of Invertebrate Diseases
General Concepts in the Ecology of Invertebrate Diseases
Ann E. Hajek1 and David I. Shapiro-Ilan2
1 Department of Entomology,, Cornell University, Ithaca, NY, USA
2 USDA-ARS, SEA,, SE Fruit and Tree Nut Research Unit, Byron, GA, USA
With the advent of molecular methods, new species of pathogens and parasites are constantly being described, and as these new species are found, we are learning more about the ecology of new invertebrate diseases, as well as diseases known for many years. Parasitism is a specific and common life-history strategy, and understanding the activity of parasites is central to community and population ecology (Bonsall, 2004). Parasitism of invertebrate hosts also has practical sides, because diseases can help to control insects in an environmentally friendly manner, but we also need to understand the ecology of diseases killing beneficial invertebrates, ranging from pollinators to clams and shrimp, in order to protect managed populations.
The ecology of invertebrate diseases is often referred to as the epizootiology of invertebrate diseases; the word epizootiology is similar to the term epidemiology but refers specifically to "the science of causes and forms of the mass phenomenon of disease at all levels of intensity in an animal population" (Fuxa and Tanada, 1987). The ecology of animal diseases, with emphasis on vertebrates, has been treated in an edited book on disease ecology (Hudson et al., 2002), followed by books emphasizing community and ecosystem ecology (Collinge and Ray, 2006; Hatcher and Dunn, 2011; Ostfeld et al., 2014).
Disease ecology with an emphasis on invertebrates was first addressed by Steinhaus (1949), specifically in relation to insects, and the treatment of this subject developed depth and breadth with the publication of an edited volume by Fuxa and Tanada (1987). Around this time, Anderson and May (1981, 1982) created models to investigate factors driving the development of disease epizootics, with at least one system involving epizootics caused by a granulovirus in a forest-defoliating lepidopteran (Anderson and May, 1980). Today, studies of the ecology of invertebrate diseases are commonly conducted, often to understand the ecology underpinning control of invertebrate pests by pathogens, or to understand protection from pathogens for invertebrates valued by humans. In addition, ecological studies of invertebrate diseases are used to build theoretical insights into the causes and dynamics of all diseases. With the wealth of knowledge that has accumulated since the last synthesis on the ecology of invertebrate diseases in 1987, it is high time to pull together information on this subject. We are also broadening the focus of this book to include the ecology of diseases of all invertebrates and not only insects. Therefore, the hosts included in this book range from pest insects like grasshoppers and caterpillars to valued insects like bees, along with marine and soil invertebrates that are important to humans or ecosystems.
In this chapter, we will present and define the basic concepts on which this field of study is built. Concepts that will be defined will be consistent with definitions in the online glossary published by the Society for Invertebrate Pathology (Onstad et al., 2006).
1.1.1 What Is Disease?
There are numerous definitions for disease, but we consider disease to be a departure from the state of health or normality. Of course, this creates a very broad characterization, including multitudes of causes. However, this book will focus on infectious diseases, which are those diseases caused by living organisms. Invertebrates are also hosts to many noninfectious diseases , of which physical and chemical injuries, genetic diseases, and cancers are a few examples. An example of no