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Other titles in this series Island Ecology M. Gorman Plant-Atmosphere Relations John Grace ModeHing John N.R. Jeffers Vegetation Dynamics John Miles AnimaI Population Dynamics R. Moss, A. Watson and J.OHason Outline Editors George M. Dunnet Regius Professor of Natural His/Ory, University of Aberdeen Charles H. Gimingham Professor of Botany. University of Aberdeen Editors' Foreword 80th in its theoretical and applied aspects, ecology is developing rapidly. In part because it offers a relatively newand fresh approach to biological enquiry, but It also stems from the revolution in public attitudes towards the quality of the human environment and the conservation of nature. There are today more professional ecologists than ever before, and the number of students seeking courses in ecology remains high. In schools as weil as universities the teaching of ecology is now widely aceepted as an essential component of biological education, but it is only within the past quarter ofa centurythat this has come about. In the same period, the journaIs devoted to publication of ecological research have expanded in number and size, and books on aspects of ecology appear in ever-increasing numbers. These are indications of a healthy and vigorous condition, which is satisfactory not only in regard to the progress of biologieal science but also because of the vita I importance of ecological understanding to the well-being of man. However, such rapid advanees bring their probIems. The subject develops so rapidly in scope, depth and relevanee that textbooks, or parts of them, soon become out-of-date or inappropriate for particular courses. The very width of the front across which the ecological approach is being applied to biological and environmental questions introduees diffieulties: every teacher handIes .his subject in a different way and no two courses are identical in content. This diversity, though stimulating and profitable, has the effect that no single text-book is likely to satisfy fully the needs of the student attending a course in eeology. Very often extracts from a wide range ofbooks must be consulted, and while this may do no harm it is time-eonsuming and expensive. The present series has been designed to offer quite a large number ofrelatively small booklets, each on a restricted topie of fundamental importanee which is likely to constitute a self-contained component of more comprehensive courses. A selection can then be made, at reasonable cost, of texts appropriate to particular courses or the interests of the reader. Each is written by an acknowledged expert in the subject, and is intended to offer an up-to-date, concise summary which will be ofvalue to those engaged in teaching, research or applied ecology as weil as to students. Studies in Ecology Inseet Herbivory I.D. HODKINSON and M.K. HUGHES Department of Biology Liverpool Polytechnic CHAPMAN AND HALL LONDON NEW YORK First published 1982 by Chapman and Hall Ltd 11 New Fetter Lane, London EC4P 4EE Published in the USA by Chapman and Hall 733 Third Avenue, New York NY 10017 © 1982 I.D. Hodkinson and M.K. Hughes l.W. Arrowsmith Ltd, Bristol ISBN-13: 978-0-412-23870-3 This paperback edition is sold subject to the condition that it shalI not. by way of trade or otherwise, be lent, resold, hired out or otherwise circulated without the publisher's prior consent in any form of binding or cover other than that in which it is published and without a similar condition induding this condition being imposed on the subsequent purchaser. All rights reserved. No part of this book may be reprinted, or reproduced or utilized in any form or by any electronic, mechanical or other means, now known or hereafter invented, induding photocopying and recording, or in any information storage and retrieval system, without permission in writing from the publisher. British Library Cataloguing in Publication Data Hodkinson, I.D. Insect herbivory.-(OutIine studies in ecology) 1. Insects-Feeding and feeds I. TitIe II. Hughes, M.K. III. Series 595.7'013 QL496 ISBN-13: 978-0-412-23870-3 Library of Congress Cataloging in Publication Data Hodkinson, I.D. (Ian David) Insect herbivory. (OutIine studies in ecology) Bibliography: p. IncIudes index. 1. Insect-plant relationships. 2. Insects-Host plants. 3. Insects-Food. I. Hughes, M.K. II. TitIe. III. Series. QL496.H63 1982 595.7'053 82-9525 AACR2 ISBN-13: 978-0-412-23870-3 e-ISBN-13: 978-94-009-5951-4 DOI: 10.1007/978-94-009-5951-4 Contents Preface Page 7 1 Introduction 9 l.l The evolutionary context and its implications l) 2 Plants as food for insects 15 2.1 Variation in the nutritive value of plant tissue 17 2.2 Barriers to the use of plant tissues 18 2.3 Trace compound barriers Il) 2.4 Dosage-dependent chemical barriers 21 2.5 Changes in plant tissue resulting from herbivory 22 2.6 Strategies of insect herbivory and plant response 22 3 Insect adaptations to herbivory 25 3.1 Finding the food: host-plant location and recognition 25 3.2 Finding the food: synchronization with the host-plant 27 3.3 Insect feeding mechanisms 28 3.4 Food utilization and conversion efficiencies 30 4 Insect herbivory and non-woody plants 35 4.1 Herbivory and the individual plant 35 4.2 Herbivory and the plant population 37 4.3 Quantitative relationships 38 5 Insect herbivory and woody plants 41 5.1 The distribution and intensity of insect herbivory 41 5.2 The consequences of herbivory for the woody plant 42 5.3 Other effects of insect herbivory 46 5.4 Insect herbivores and tree rings 47 6 Insect herbivory and the plant community 49 6.1 Plant community composition and insect abundance 49 6.2 Effects of insect herbivory on plant communities 50 7 Inseet herbivory in eeosystems 55 7.1 The scale of insect herbivory 55 7.2 The role of insect herbivores in the ecosystem 56 7.3 Insect herbivory and agricultural ecosystems 62 References 65 Index 73 Preface This book attempts to summarize what we know about inseet-plant relationships without beeoming too involved with untestable hypo theses. It is not intended to be eomprehensive and we have deliberately excluded diseussion of aquatie organisms and fungi. Our definition of inseet herbivores is intentionally broad. It includes all inseets whieh feed on plants, although we have emphasized those whieh feed primarily on the photosynthetie tissues. Some referenee is made to seed predation but pollination eeology is excluded. We thank Ors P.H. Smith and M. Luxton for their helpful eommenb on the manuseript but we accept full responsibility for any mistakes whieh may remain. Finally, we thank the various publishers and a uthor~ who gave us permission to use copyright material. 7 I Introduction The net primary produetion of the 300000 speeies of vaseular plant whieh inhabit the dry land surfaee of the earth has been estimated at about 115 x 10 9 t per annum. This represents a massive resouree potentially available for exploitation by the herbivorous inseets, which themselves probably number in exeess of 500000 species. The impaet of inseets on agrieultural erops has been documented sinee biblical times when plagues of loeusts were 'all over the land of Egypt'. In contrast an understanding of their impact on and interaction with natural vegetation has only really developed over the last hundred years. In natural ecosystems widespread outbreaks of herbivorous insects, leading to eomplete defoliation of vegetation, happen only sporadieaJly. The most speetacular examples tend to oceur in the low diversity forests of the eool temperate or subarctie regions of the earth. For example, within the last eentury population eruptions of the moth speeies belonging to the genera Oporinia and Operophtera havc lead to widespread defoliation and death of birch forest in northern Finland and along the Seandinavian mountain ehain [1]. It has been suggested that such outbreaks are rare in the more diverse tropieal forests but reeent work in Panamanian lowland rain forest, involving the moth Zunacetha annulata and its larval host plant tree Hybanthus prunifo/ius, has shown that such outbreaks do oceUf, but they are le ss visuaJly obvious in such habitats [2]. Thus while heavy defoliation of plants does oeeUf it is the exeeption rather than the rule: in general, phytophagous insects consume only a fraction of the available primary produetion. This book sets out, therefore, to examine the ways in whieh herbivorous inseets exploit their food reSOUfee and the means by whieh plants seek to minimize their depredations. It attempts to present a quantitative analysis of inseet herbivory set against the baekground of the eeologieal communityand ecosystem. 1.1 The evolutionary perspective and its implications The earliest known forms of inseet are thought to have been detritus feeders. The habit of plant feeding appears to have evolved in dependently on several oeeasions, even within a single order such as the Hymenoptera [3]. In eonsequenee the herbivorous habit is widespread, but disjunetively displayed, aeross the different inseet groups. Fig. 1.1 illustrates the evolution of the mai n plant-feeding inseet orders relative to that of the major plant groups. Particular attention should be paid to the fact that the flowering plants or Angiosperms, the group whieh 9 Mesozoic Devon Car~r :4= Perm Trias. Jur. Cret. Tertiarv Recent PLANTS algae ferns mOSSE Gymn sperms Angio: perms mana ots grassl S I NSECTS Orthc Itera Thysa optera Hemi Itera Colec tera Hyme optera Diptel a IsoptE ra Lepid optera I I I I I 350 300 250 200 150 100 50 o Mi llian Years Befare Present (B P) Fig. 1.1 Evolutionary chronology of the major orders of herbivorous inseets and the major gwups of liying plants.