Insect virus diversity: The Insect Viruses, edited by L.K. Miller and L.A. Ball

Abstract

Plenum Press, 1999 $125.00 hbk (xvii + 413 pages)ISBN 0 306 45881 0The most recent report of the International Committee on the Taxonomy of Viruses lists 26 virus families that infect vertebrates but only nine that infect invertebrates, primarily insects. However, as insects make up more than half of the world’s known animal species, there are undoubtedly many more insect viruses still to be discovered. Not surprisingly, some of the first insect viruses to be described infected bees or silkworms or caused the demise of insect pests. To date, our knowledge of insect viruses is still limited mainly to families infecting insects that impact on human lives. Insect viruses have been observed in many insect orders, but the best characterized families have been isolated from the Lepidoptera, Coleoptera, Hymenoptera, Diptera and Orthoptera.The known virus families are as diverse and fascinating as their insect hosts. They come in all sizes and shapes, have diverse genomic compositions and their relationships with their hosts range from virulent to symbiotic. Many are related to well known vertebrate and plant virus families; for example, the entomopoxviruses, densoviruses and iridoviruses are related to vertebrate poxviruses, parvoviruses and iridoviruses, respectively, and cypoviruses are related to vertebrate and plant reoviruses. Like the baculoviruses, but in contrast to their vertebrate and plant virus counterparts, entomopoxviruses and cypoviruses are occluded in proteinaceous inclusion bodies that protect them in the environment until they can infect a new host. Interestingly, the occlusion proteins are not related to each other or to the baculovirus occlusion protein polyhedrin, but evolved independently in each of these virus families; this highlights the importance of environmental stability for the transmission of these viruses. Others, like polydnaviruses and ascoviruses, are quite unique. The polydnaviruses are intimately associated with parasitic wasps. Their multipartite genomes are integrated within the wasp genome and are transmitted vertically. The virus replicates and the virions produced in the reproductive tracts of the female wasp are then injected into parasitized caterpillars along with the wasp eggs. In the caterpillar host, polydnavirus genes are expressed that suppress the host immune system. Ascoviruses have an unusual effect on infected cells; during replication, ascovirus-infected cells are cleaved into sac-like vesicles.The Insect Viruses provides an up-to-date review of all of the characterized insect viruses except the baculoviruses, which have their own volume in the series. This volume is timely because of the renewed interest, over the past decade, in families of insect viruses other than the baculoviruses and because of the wealth of new information that is available, much of it gained using the tools of modern molecular biology. The book is organized roughly by virus size and genome starting with the large DNA viruses and proceeding through discussions of the RNA viruses. Different virus families are treated in separate chapters. Other chapters cover interesting viruses that are currently unclassified and structural studies of small icosahedral viruses. Although the biology of arboviruses is not covered in this volume, the final chapter focuses on their utility in transforming insect disease vectors and their use as tools for studying the transmission of viruses by insect vectors. The book is well written and each topic is covered by acknowledged experts in the field. Because both the extent and types of information available on each topic differ, some chapters focus more on recent findings or on specific aspects of the topic, while providing references to previous reviews. Other chapters provide more comprehensive coverage.Although there is no formal unifying theme, it could be: why study insect viruses? In the preface the editors highlight the myriad reasons for studying insect viruses. The authors of each individual chapter then reiterate these points by emphasizing the value in studying the virus family discussed in that chapter. Like the baculoviruses, entomopoxviruses, tetraviruses and densonucleoviruses have potential as biological insecticides or expression vectors. Others provide insights on virus structure and assembly, virus–host interactions and virus evolution. I especially appreciated the discussions of new insights on virus evolution and diversity made possible by the comparisons of virus sequences and genomic structures that were presented in several chapters.The Insect Viruses belongs on the shelves of insect pathologists, especially insect virologists, right next to The Baculoviruses. This book will also be useful to researchers in other fields who will appreciate the diversity and utility of these viruses: virologists and students of virology, particularly those interested in virus evolution or structure, entomologists interested in biological control of insects, insect immunity or diseases carried by insect vectors, and biotechnologists immediately spring to mind.