Advances in Disease Vector Research PDF
Preview Advances in Disease Vector Research
Advances in Disease Vector Research Advances in Disease Vector Research Edited by Kerry F. Harris Virus Vector Laboratory, Department of Entomology, Texas A&M University, College Station, Texas 77843, USA Editorial Board Willy Burgdorfer Epidemiology Branch, Rocky Mountain Laboratories, Hamilton, Montana 59840, USA Paul E.M. Fine Ross Institute, London School of Hygiene and Tropical Medicine, London WCl, United Kingdom Richard I.B. Francki Virus Laboratory, The University of Adelaide, Waite Agricultural Research Institute, Glen Osmond, South Australia 5064 Edouard Kurstak Comparative Virology Research Group, Department of Microbiology and Immunology, Faculty of Medicine, University of Montreal, Montreal H3C 317, Canada JohnJ. McKelvey, Jr. Associate Director of Agricultural Sciences for the Rockefeller Foundation (Retired). Richfield Hill Farm, Route 1, Box 144-A, Richfield Springs, New York 13439, USA Benny Raccah Department of Virology, The Volcani Center, Bet Dagan, Israel Robert K. Washino Department of Entomology, University of California at Davis, Davis, California 95616, USA Robert R. Whitcomb Plant Disease Vector Laboratory, SEA-USDA, B465, Beltsville, Maryland 20705, USA Telford H. Work Department of Medical Microbiology and Immunology, School of Medicine, University of California at Los Angeles, Los Angeles, California 90024, USA Advances in Disease Vector Research Volume 7 Edited by Kerry F. Harris With Contributions by C.l. Andrews R.H. Bagnall N. Carter C. Chastel l.R. DeLoach K.S. Gibb R. Harrington 1. Humphery-Smith 1. Maudlin l. W. Randles R. C. Sinha G. Spates With 31 Illustrations Springer-Verlag New York Berlin Heidelberg London Paris Tokyo Hong Kong Barcelona Kerry F. Harris Virus Vector Laboratory Department of Entomology Texas A&M University College Station, Texas 77843, USA Volumes 1 and 2 of Current Topics in Vector Research were published by Praeger Publishers, New York, New York. ISSN: 0934-6112 Printed on acid-free paper © 1991 Springer-Verlag New York Inc. Softcover reprint of the hardcover 1st edition 1991 Copyright is not claimed for works by U.S. Government employees. All rights reserved. This work may not be translated or copied in whole or in part without the written permission of the publisher (Springer-Verlag New York, Inc., 175 Fifth Avenue, New York, NY 10010, USA), except for brief excerpts in connection with reviews or scholarly analysis. Use in connection with any form of information storage and retrieval, electronic adaptation, computer software, or by similar or dissimilar methodology now known or hereafter developed is forbidden. The use of general descriptive names, trade names, trademarks, etc., in his publication, even if the former are not especially identified, is not to be taken as a sign that such names, as understood by the Trade Marks and Merchandise Marks Act, may accordingly be used freely by anyone. Typeset by Best-set Typesetter Ltd., Quarry Bay, Hong Kong. 9 8 7 6 5 432 1 ISB N -13 : 978-1-4613-9046-6 e-ISB N -13 : 978 -1-4613-9044-2 DOl :10.1007/978-1-4613-9044-2 Preface We open Volume 7 with a series of four chapters on plant virus transmission by insects. In Chapter 1, Karen Gibb and John Randles present preliminary information about an association between the plant bug Cyrtopeitis nicotianae (Heteroptera: Miridae) and velvet tobacco mottle virus (VTMo V): the only reported instance of mirid transmission of a known virus. Mirids could be considered as likely vectors of plant viruses because they are phytophagous, possess a piercing-sucking-feeding apparatus, have winged adults, and are cosmopolitan pests of a wide range of crops. Surprisingly, however, there are only three plant viruses purportedly transmitted by heteropterous vectors, compared with the nearly 250 by homopterous ones. To what extent these figures reflect actual differences in the abilities of members of the two suborders to transmit plant pathogens remains to be determined. Compared with the Homop tera, the Heteroptera have been ignored by researchers as potential vectors of plant viruses. The authors are quick to point out that additional studies are needed before generalizations can be made about virus-mirid-plant interactions and that virus transmission by mirids is not easily characterized using the conventional transmission criteria and terminology established for such homopterous vectors as aphids and leafhoppers. Transmission of VTMoV by C. nicotianae appears to have characteristics in common with both nonpersistent noncirculative and circulative (persistent) transmission. However, because there is no evidence to associate the virus with the salivary glands of its vector, the authors hypothesize that the virus "translocates" in its mirid vector rather than circulates (i.e., virus enters the vector through the maxillary food canal and exits via the salivary canal). The possibility of transmission via an ingestion-defecation pathway is discussed, as are similarities between virus transmission by mirids and that by beetle and mite vectors. In Chapter 2, Nick Carter and Richard Harrington discuss the many factors affecting aphid population dynamics and behavior and their subsequent influence on aphid-borne virus spread: all from an entomolo- v Preface VI gist's viewpoint. The authors first examine the influence of various weather factors on aphid overwintering survival, spring population development, dispersal from winter host plants, and virus spread within crops. They then describe how intrinsic characteristics of the vectors influence virus spread, such as their tendency to produce winged or sexual forms. The roles of aphid natural enemies and noncrop plants in virus spread are also discussed, the latter of which harbor crop viruses, vectors of crop viruses, or both. In the final section, the authors address the question of how such crop management practices as rotation, sowing dates, and pesticide usage influence virus spread though their effects on vector populations. The influences of these various factors on nonpersistent, semipersistent, and persistent virus transmission are discussed in a comparative manner. Applications of the resulting information to forecasting are considered also, although the authors agree that most efforts in this direction are relatively undeveloped due to the complexity of both the factors involved and their interactions. In Chapter 3, Richard Bagnall will arouse no doubt the interest of more than a few epidemiologists and climatologists with his theory regarding the cyclic nature of aphid-borne potato virus epidemics in northern latitudes during recent times. There have been three major epidemics of the potato leaf roll virus (PLRV) in the seed-growing areas of northern Maine and New Brunswick, as well as in northwestern Europe during the 20th century. These events have occurred at approximate 32-year intervals, virtually in phase sequence with earlier outbreaks of "the curl," a "degeneration" disease of potatoes known in Europe during the 18th and 19th centuries. The characteristics of the epidemics, their regular occur rence, and coincidences with periodic natural phenomena-periods of warm climate and drought, and certain sunspot minima-point to the workings of a widespread climatic cycle. In New Brunswick, the potato mosaic diseases, due to potato viruses Y and A (PVY and PVA) , were found also to fluctuate in a cyclic pattern, but a different one from that of PLRV. This mosaic cycle, averaging 9.3 years, runs clearly out of phase with the sunspot cycle, but has been in phase during the past 66 years with a population cycle in Canadian wildlife known as the Canada Hare-Lynx Cycle. A possible connection is that the hare thrives on an abundance of many of the same shrubs and trees on which aphids lay eggs. The difference between the two cycles derives from the different modes of transmission of the viruses. The persistently transmitted PLRV is transmitted largely by the potato-colonizing aphid, Myzus persicae (Sulz.), which does not overwinter readily in New Burnswick. And PLRV outbreaks have occurred during discrete 5-10 year periods of milder climate. By contrast, the nonpersistent PVY can be transmitted by numerous aphids that do not necessarily colonize potatoes, but visit in search of feeding sites. Many of these aphids are better adapted to the Preface vii northern climate. Moreover, the Canada hare-lynx cycle is reputed to be a northern phenomenon. The mosaic disease cycle in New Brunswick is actually more complex. During the most recent cycle, the relatively intense spread of the major virus, PVY, occurred only during alternate even years (1974, 1976, 1978, 1980, and 1982): a biennial rhythm. After a double low (1983 and 1984), a new cycle has begun with highs in odd years (1985 and 1987). In effect, there has been an intense spread in only 7 of the past 16 years, with no 2 in succession. This rhythm has a significant bearing on the status of New Brunswick as a seed-growing area. In addition, spread of the latent potato virus S was found to be subject to the same biennial rhythm as is PVY. Therefore, it is held to be spread in a nonpersistent manner by many of the same aphids. The author also points out that both the PLRV and mosaic cycles may be affected further by longer-term climatic change. If the sharp rise in northern hemisphere temperature since 1970 continues, the PLRV epidemics may become more frequent or prolonged. Conversely, the warming and drying that occurred in the 1930s and 1940s coincided with a decline both in the lynx harvest and in the incidence of mosaic diseases. Chapter 4 is dedicated to the memory of Dr. Yogesh Paliwal, who passed away on June 23, 1988. Authors Chris Andrews and Ramesh Sinha describe the aphid vectors of barley yellow dwarf virus (BYDV), which causes a major disease in cereal crops throughout the world, and discuss the effects of the virus on the ability of winter cereal plants to withstand the winter stresses that influence the plants in the northern part of their range. Current views of the relationships between the various virus strains are given, with a description of their aphid vectors, and a survey of the epidemiology of the disease. After a brief review of the effects of freezing stresses on plants, the effects of BYDV on overwintering cereals are described from a series of field studies. Experiments in controlled environments are reviewed that separate BYDV effects on cold-hardiness, ice-tolerance and low-temperature-flooding tolerance. Another section describes some of the biochemical associations between virus infection and stress-tolerance reduction, and the chapter concludes with speculation on the precise nature of the interaction and possibilities for increasing the tolerance of plants to the virus. Beginning with Chapter 5, we switch our attention to human and animal disease associations with blood-feeding flies. In this chapter, authors John Deloach and George Spates give us a brief but thorough review of the limited literature on artificial diets, "truly defined diets," for stable flies and tsetse flies. The rather unusual combination of these strikingly different arthropods in one review stems from the fact that stable flies were used for dietary model studies in Texas, the authors' home base, whereas tsetse flies were used elsewhere in Europe, Africa, and Canada. The authors begin by defining and categorizing diets for blood-feeding viii Preface arthropods and the approaches taken to developing them. Most of the research on artificial diets for blood-feeding insects has been directed by only a few laboratories, and the Tsetse Research Laboratory in Bristol, England, is one such center that has made significant contributions in this regard. Indeed, the authors were aided in their review because of their collaboration over the past 10 years with researchers at both the Tsetse Research Laboratory and the International Atomic Energy Agency in Vienna, Austria. Basically, animal blood was dissected into its various components (blood cells and plasma) and subsequently subdivided into proteins and fats. Albumin, hemoglobin, phospholipids, and cholesterol are dietary requirements for both Stomoxys and Glossina. It is unlikely that amino acids comprising the proteins can be substituted for albumin or hemoglobin because of the high osmotic pressure of the amino acid solutions. Although significant progress has been made, there remain several unanswered questions regarding artificial diets for blood-feeding insects. In Chapter 6, Ian Maudlin discusses interactions among the tsetse immune system, symbionts, and parasites that are crucial to transmission of African trypanosomiasis. Until recently, transmission of the African trypanosomiases was thought to depend largely on fly number: every tsetse in a population was regarded as a potential vector. Maudlin here reviews the evidence that led to this view and describes recent experimental work which, together with field data, shows that most tsetse flies in a popUlation, in fact, are refractory to infection. The basis of this refractoriness is shown to lie in the tsetse immune system that is equipped specifically with lectins to deal with incursions by trypanosomes. Refractoriness to trypanosomes can be inhibited by symbionts that inhibit lectin output, rendering flies carrying these bacteria susceptibles. Intriguingly, this insect defense system has been put to use by the trypanosome to act as a trigger to complete its life cycle in the fly. That the tsetse immune system should be involved so closely in the transmission of the disease is an important finding and has clear implications for research on other vector-parasitc relationships. The volume ends with Chapter 7, a thorough and timely treatise on mosquito spiroplasmas by Claude Chaste I and Ian Humphery-Smith. For a group of organisms as well studied as mosquito vectors, it is surprising that mosquito spiroplasmas (msp) were not discovered prior to 1982. This event closely followed the development of suitable culture media and since has made possible the isolation of several msp and the description of Spiroplasma culicicola from the United States, S. sabaudiense from France and S. taiwanense from the Far East. Less than 10 years has elapsed since the initial discovery of msp by Slaff and Chen, and although our knowledge of these organisms has increased greatly, the amount of information represents merely the tip of an iceberg. Some researchers have even suggested that spiroplasmas may one day be shown to be as diverse as their arthropod hosts. Once more research groups start looking for msp in Preface IX a systematic fashion, undoubtedly more msp will be uncovered. And the authors have purposefully included details pertaining to isolation techni ques to further that end. At the very least, the Cantharis spiroplasma complex, isolated from mosquitoes, plants, and other anthropods, probably circulates in nature via flower nectar. However, much needs to be clarified before the ecology of msp is appreciated fully. Real hope is sustained for the eventual use of msp as biological control agents against mosquito vectors of tropical disease and mosquito species of nuisance value for urban dwellers of the world's major cities. Finally, the possible role of thermophilic spiroplasmas (as yet no msp) as causative agents of degenerative central nervous system disorders makes this field both exciting and of potential relevance to both human and animal health. I thank the authors for their scholarly contributions as well as their patience and diligence in working with me to bring Volume 7 to such a successful conclusion. This volume contains information of interest to most biologists, but in particular to plant pathologists, virologists, microbiolo gists, vector ecologists, disease epidemiologists, both medical and veterin ary arthropodologists and parasitologists, and even climatologists. I humbly and gratefully acknowledge the encouragement and technical assistance of the members of the Editorial Board and staff of Springer Verlag. Without their assistance, my job would not be nearly so rewarding. Kerry F. Harris Contents Preface...... .............................................. v Contributors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xv Contents of Previous Volumes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xvii 1 Transmission of Velvet Tobacco Mottle Virus and Related Viruses by the Mirid Cyrtopeltis nicotianae Karen S. Gibb and John W. Randles ........................ 1 Introduction ............................................ 1 Characteristics of Transmission ............................ 3 The Paradox of Persistence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 Relationship of Virus Distribution to Transmissibility ......... 11 Conclusion ............................................. 14 References ............................................. 16 2 Factors Influencing Aphid Population Dynamics and Behavior and the Consequences for Virus Spread Nick Carter and Richard Harrington ........................ 19 Introduction ............................................ 19 Weather. ..... . . . . . . . . . ...... .. . . . . . . .... . . . . . ...... . . . . 22 Biotic Factors ........................................... 34 Crop Management ....................................... 38 Summary............................................... 42 References ............................................. 43 3 Cyclic Epidemics of Aphid-Borne Potato Viruses in Northern Seed-Potato-Growing Areas Richard H. Bagnall ...................................... 53 Introduction ............................................ 53 The Curl in Potatoes-1750 to 1905 . . . . . . . . . . . . . . . . . . . . . . . . . 53 Potato Leaf Roll .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56 Potato Mosaic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61 xi
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