Insect Pathology Second Edition Fernando E. Vega Sustainable Perennial Crops Laboratory United States Department of Agriculture Agricultural Research Service Beltsville, Maryland Harry K. Kaya Department of Nematology University of California Davis, California AMSTERDAM l BOSTON l HEIDELBERG l LONDON l NEW YORK l OXFORD l PARIS SAN DIEGO l SAN FRANCISCO l SINGAPORE l SYDNEY l TOKYO Academic Press is an Imprint of Elsevier Academic Press is an imprint of Elsevier 32 Jamestown Road, London NW1 7BY, UK 225 Wyman Street, Waltham, MA 02451, USA 525 B Street, Suite 1800, San Diego, CA 92101-4495, USA First edition 1993 Second edition 2012 Copyright Ó 2012, 1993 Elsevier Inc. All rights reserved. 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Because of rapid advances in the medical sciences, in particular, independent verification of diagnoses and drug dosages should be made British Library Cataloguing-in-Publication Data A catalogue record for this book is available from the British Library Library of Congress Cataloging-in-Publication Data A catalog record for this book is available from the Library of Congress ISBN: 978-0-12-384984-7 For information on all Academic Press publications visit our website at elsevierdirect.com Typeset by TNQ Books and Journals Pvt Ltd. www.tnq.co.in Printed and bound in China 1213141516 10987654321 Chapter 1 Scope and Basic Principles of Insect Pathology y Harry K. Kaya* and Fernando E. Vega * University of California, Davis, California, USA, y United States Department of Agriculture, Agricultural Research Service, Beltsville, Maryland, USA Chapter Outline 1.1. Introduction 1 1.3.6. Pathogenicity and Virulence 7 1.2. Categories of Disease 3 1.3.7. Dosage 8 1.3. Basic Principles in Insect Pathology 3 1.3.8. Signs, Symptoms, and Syndromes 8 1.3.1. Entomopathogens 4 1.3.9. Course of Infection 8 1.3.2. Some Major Classification and Taxonomic 1.3.10. Acute, Chronic, and Latent Infections 9 Changes 4 1.3.11. Koch’s Postulates 10 1.3.3. Portal of Entry 5 1.3.12. Diagnosis 11 1.3.4. Microbial Toxins 5 References 11 1.3.5. Infectivity 7 SUMMARY occurring in freshwater systems (Daly et al.,1998). More Insects are the dominant animals in the world, with more than one than 99% of the approximately one million described insect million described species. The vast majority of insects are species (Grimaldi and Engel, 2005) are either innocuous or innocuous or beneficial to humans, but a small percentage are beneficial to humans, such as the silkworm (Bombyx mori), pests that require a significant amount of our time, effort, and cochineal scale (Dactylopius coccus), pollinators, and funds to reduce their negative effects on food production and our parasitoids and predators (Gullan and Cranston, 2005; health and welfare. One environmentally acceptable method to Pedigo and Rice, 2009). To place this in another context, control these insect pests is to use pathogens. The study of path- only 1% of the known insect species are our competitors that ogens infecting insects is referred to as “insect pathology”. Insect vie for our crops and stored products, damage our belong- pathology is the study of anything that goes wrong with an insect and, therefore, includes non-pathogenic and pathogenic causes. ings, serve as vectors for plant pathogens, or are of medical The present focus is on pathogens that can be used as microbial or veterinarian importance by feeding on us or our livestock control agents of insects. Here, the basic principles in insect and pets and, in some cases, serving as vectors of disease pathology including the microorganisms that cause diseases, their agents to humans and other vertebrates (Pedigo and Rice, classification and phylogeny, portal of entry, infectivity, patho- 2009). Even though the number of insect pest species is genicity and virulence, course of disease, Koch’s postulates, and small compared to the number of described insect species, diagnosis are covered. they require a significant amount of our time, effort, and funds to reduce their negative effects on food production and our health and welfare. 1.1. INTRODUCTION One of the main tactics to control insect pests is the use of chemical pesticides. Unfortunately, the application of Insects represent three-quarters of all animal species in the chemical pesticides can (1) have a negative effect on human world, with the vast majority of them being terrestrial and/or health and the environment; (2) result in resistance of the pest Insect Pathology. DOI: 10.1016/B978-0-12-384984-7.00001-4 1 Copyright Ó 2012 Elsevier Inc. All rights reserved. 2 Insect Pathology species to pesticides; and (3) kill or negatively affect non- Before the development of microbial control agents as target organisms. An alternative to chemical control is bio- management tools for insect pests, maladies had been logical control (or biocontrol), which is the study and use of recorded from beneficial insects for a long time. Thus, the living organisms for the suppression of population densities discipline of insect pathology dates back to over 2000 years of pest insects (Eilenberg et al.,2001). The living organisms ago when the Chinese recorded diseases in the silkworm are predators, parasitoids and entomopathogens (meaning and the Greeks noted diseases in the honey bee, Apis microorganisms capable of causing diseases in insects; from mellifera (see Chapter 2). Through the ages, many diseases the Greek entoma ¼ insect, pathos ¼ suffering, gennaein ¼ have been discovered and described from both beneficial to produce, synonymous with “insect pathogens”). and pestiferous insects. This early development of the The use of microorganisms for biological control is discipline can be attributed to (1) the curiosity of scientists commonly referred to as microbial control, an approach in describing and ascertaining the cause of pathological that includes four strategies: classical, inoculation, conditions in insects; (2) the need to find cures for diseases inundation, and conservation (Eilenberg et al.,2001). that afflicted beneficial insects; and (3) the potential use of Classical biological control involves the intentional pathogens to control insect pests. importation, release and establishment of entomopath- What is insect pathology? Broadly defined, insect ogens into a new environment. Inoculation biological pathology is the study of anything that goes wrong [i.e., control deals with the release of an entomopathogen with disease (“lack of ease”)] with an insect. Disease is a process the expectation that it will multiply and will provide that represents the response of the insect’s body to insult or temporary control. This approach is sometimes referred injury (Steinhaus, 1949, 1963c). Often, it is not easy to to as augmentation biological control. Inundative bio- separate a healthy insect from one that is diseased owing to logical control is dependent upon the release of signifi- the absence of symptoms. Steinhaus (1963c) differentiates cant amounts of inoculum of an entomopathogen to a healthy insect from a diseased one as follows: “A healthy provide immediate control of the pest; control ensues insect is one so well adjusted in its internal environment from the release inoculum and not from its progeny. and to its external environment that is capable of carrying Conservation biological control involves the modification on the functions necessary for its maintenance, growth, of the environment to protect and enhance an established and multiplication with the least expenditure of energy. entomopathogen. An entomopathogen can also be judi- A diseased insect is simply one that is not healthy; it is an ciously used with chemical pesticides in an integrated insect that can no longer tolerate an injury or hardship pest management program (Tanada and Kaya, 1993)or without having an abnormal strain placed upon it.” combined with a chemical substance(s) that enhances its The scope of insect pathology encompasses many effectiveness as a microbial control agent (Koppenho¨fer subdisciplines in entomology (Fig. 1.1). In ecology, for et al., 2002; Koppenho¨fer and Fuzy, 2008). example, epizootics of viral, bacterial, fungal, FIGURE 1.1 Relationship between insect pathology and other subdisciplines in entomology. Chapter | 1 Scope of Insect Pathology 3 microsporidian, and nematode diseases can cause signifi- injuries caused by parasitization or infestation by other cant mortality to devastate insect populations. In physi- insects or arachnids or by predation. For more detailed ology, biochemistry, and toxicology, diseased insects will information on diseases caused by non-infectious agents, affect the results of the experiments with differences in the reader is referred to Steinhaus (1963a,