Table Of ContentPOPULATION BIOLOGY
OF TROPICAL INSECTS
POPULATION BIOLOGY
OF TROPICAL INSECTS
ALLEN M. YOUNG
Milwaukee Public Museum
Milwaukee, Wisconsin
PLENUM PRESS • NEW YORK AND LONDON
Library of Congress Cataloging in Publication Data
Young, Allen M.
Population biology of tropical insects.
Bibliography: p.
Includes index.
I. Insect populations - Tropics. 1. Title.
QL491.6. Y68 595.7'05248'0913 82-7562
ISBN-13: 978-1-4684-1115-7 e-ISBN-13: 978-1-4684-1113-3 AACR2
001: 10.1007/978-1-4684-1113-3
©1982 Plenum Press, New York
Softcover reprint of the hardcover 1st edition 1982
A Division of Plenum Publishing Corporation
233 Spring Street, New York, N.Y. 10013
All rights reserved
No part of this book may be reproduced, stored in a retrieval system, or transmitted
in any form or by any means, electronic, mechanical, photocopying, microfilming,
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"Internarse en un bosque es reconciliarse con la vida. El asombro
resbala de hoja en hoja. La fecundidad telurica palpita y destella, como
una libelula dorada, en los oblicuos rayos solares que se filtran por entre
los densos ramajes."
.... From "Bosques Y Vagabundos," by Carlos Luis Altamirano
La Nacion (seccion Ancora), San Jose, Costa Rica
November 12, 1978
PREFACE
In this book I have tried to bring together the major developments in the study of
insect populations in tropical environments. In some ways, this task has been a
difficult one because conceptually it is virtually impossible to limit a discussion
of insect ecology to the tropics, since the same concepts, theories, and hypoth
eses concerning the mechanisms by which habitats support insect populations
often apply both to temperate and to tropical regions. Thus one might argue
effectively that a book such as Peter Price's Insect Ecology represents a more
comprehensive treatment of insect ecology, including the tropical aspects. Yet
because there has been a tremendous amount of new study on insects in the
tropics in recent years, and because there has also been a strong historical interest
in tropical insects, judging from early museum expeditions and medically and
agriculturally oriented studies of insects in the New and Old World tropics, I
believe there is a place for a book dealing almost exclusively with tropical
insects. But logically so, such a book by necessity incorporates data and informa
tion from Temperate Zone studies, if for no other reason than because insights
into the properties of tropical environments often emerge from compariso'ns of
species, communities, or faunas between temperate and tropical regions. An
understanding of insect populations in the tropics cannot be divorced from a
consideration of Temperate Zone populations.
The book is unabashedly biased to the New World tropical studies because
of my interests and more proximal awareness of research on insects being con
ducted in this region. But a valid attempt is made to incorporate research studies
from the Old World tropics.
The basic mission of this book is to bring together various concepts and
studies related to the issue of explaining the spatial and temporal patterns of
insect diversity in the tropics, considering the breeding population of a species to
be the major ecological unit beyond the individual within the population. The
population is interacting with both biotic and physical components of the envi
ronment, within and between habitats, and regionally. Much of tropical insect
population biology is therefore concerned in different ways with describing pat
terns of distribution of individual species in relation to resources and other
environmental factors.
There is also a need for detailed descriptive data on the natural history of
vii
viii PREFACE
individual species in particular habitats in the tropics. What are some of the
major attributes underlying observed patterns of distribution? Can we recognize
the roles of biotic control agents in influencing the populations of insect species
as well as the role of abiotic factors? We recognize that the tropical regions of the
world are extremely heterogeneous in terms of climatic factors and the patterns of
fluctuation of these factors. The kinds of selection pressures affecting an insect
species on a mountain top in the tropics may greatly differ from those affecting
the same species or a closely related species in an adjacent lowland area. Within
major climatic areas, varying subclimatic conditions will be arising from
localized weather patterns and effects of topography and kind of vegetation
cover. Selection pressures on many insect species may be very different in a
strongly seasonal region than in a relatively nonseasonal tropical region.
The fine tuning of insects and their resources, as exemplified by many
plant-insect interactions in the tropics, may reflect coevolved interactions be
tween insects and their resources, and in recent years there has been a great
interest in defining the traits or properties of such associations. Emerging from
such work is the concept of the individual green plant as an extremely
heterogeneous resource for insects, in the sense that defense systems against such
herbivores vary among different parts of the plant and as a result of highly
localized environmental conditions at anyone point in time and changes in the
environment through ecological and evolutionary time. Herbivore pressure may
be a function of the ability of insect species to adapt to the defensive chemistry of
plants selected as hosts. Herbivore pressure is also a function of (1) diurnal or
seasonal cycles in defensive chemistry metabolism and (2) the degree to which
herbivores synchronize feeding with phases of low concentration of defensive
compounds in specific plant structures targeted as food. Much of our understand
ing of insect-plant interactions comes from studies in the tropics.
Tropical insect studies also point to the need to consider the success of an
insect species in a particular habitat or geographical region to be a function of
behavioral and physiological flexibility instead of evolutionary adaptations, i.e.,
genetic variation in populations. Neotropical species of Drosophila may be
capable of feeding on a variety of qualitatively different kinds of food not so
much because populations of these flies are heterogeneous genetically, but be
cause behavioral flexibility enables individual flies to effectively exploit the
range of available food types or breeding sites.
Understanding the occurrence of regions in the tropics of high species
richness for insect taxa is a function of the analysis of historical (biogeographi
cal) events and ecological factors. In recent years there has been increased study
of forest refugia in Central and South America in relation to periods of recent
glaciation, and such studies have increased our understanding of why pockets of
high species richness are surrounded by areas of relatively low richness. Ecologi
cal factors, including the occurrence of natural and human-induced changes in
habitats in the tropics-the latter through agriculture, lumbering, and population
PREFACE ix
expansions-also shape the distribution of insect species and the kinds of re
sources they exploit in a particular area. An attempt is made to examine the
properties of insect populations in such man-made environments as well as the
effects of natural succession on species.
Basic research studies on the mechanisms of insect-plant interactions in the
tropics provide mankind with new information about the unique and regulatory
properties of natural products, data that have the potential to be translated into
applied use through biotechnology as related to the development of naturally
based repellents, insecticides, and fungicides. Tropical floras represent a millieu
of novel and diverse mechanisms of chemical defense against herbivores, and the
insects exploiting such resources have developed detoxification enzyme systems
and other means of countering the defenses of plants. Such interactions provide a
basis for the development of new and effective methods of control for pests and
pathogens associated with Temperate Zone crops and forests. The study of tropi
cal insects and their interactions with their resources has great potential to the
application of natural products to new research in agriculture, horticulture,
pharmacology, etc. But the first step in reaching such applications is to determine
what is out there, to examine the patterns of distributions of species or groups of
species and genera, to find out what causes the observed patterns, and in the case
of insect-plant interactions to elucidate the mechanisms holding such relation
ships together and their genetic, physiological, or behavioral basis.
I have attempted to summarize a bulk of the pertinent literature on tropical
insect popUlation biology, with an emphasis on research done within the last 50
years. This book can serve as a helpful starting point for undergraduate and first
or second-year graduate students with interests in ecology or environmental
biology.
I wish to thank all of the biologists who consented to copyright permissions
from their publications. Mary Joan Young offered encouragement during the
preparation of the manuscript. Dr. Theresa A. Noeske provided painstaking
technical assistance. Karen Heerhold did an excellent job of typing the final
draft of the manuscript. The guidance and cooperation of Ellis Rosenberg and
his staff at Plenum are also appreciated. Gerald R. Noonan reviewed Chapter 10.
I am grateful for the encouragement and strong vote of confidence given to me
by my good friend Oskar R. Zaborsky with the initial plan to write this book. My
own field work experience in the tropics covers a 12-year period, with support
from the Organization for Tropical Studies, Inc., the Associated Colleges of the
Midwest and Lawrence University, the National Science Foundation, Friends of
the Milwaukee Public Museum, and the American Cocoa Research Institute. I
owe a great deal to these people and sources of funding for making my field
work possible.
Allen M. Young
Milwaukee
CONTENTS
1. The Faunistic Richness of Insects in the Tropics: A Brief Overview 1
2. Individual and Population Responses to Environments . 19
2.1. Ecological Response . . . . . 19
2.2. Natural Selection . . . . . . 22
2.3. Some Properties of Populations. 22
2.4. Ecological Diversity and the Tropics 26
2.5. Some Mechanisms Underlying Tropical Insect Density 32
2.6. Strategies of Response to the Environment 33
2.7. Natural Selection and Properties of Populations 40
2.8. Environmental Predictability and Response Patterns 50
3. Machinery of Environmental Response Mechanisms in Insects: Key
to Evolutionary and Ecological Diversification 61
3.1. Notes on Insect Diversity 61
3.2. Comments on Insect Physiology 67
3.3. Integration of the Insect Phenotype by Hormonal Systems: A Brief
Review 71
3.4. Diapause and Migration in Insect Populations: Escape in Time
and Space. 74
3.5. Temperature, Photoperiod, and Other Factors Related to Insect
Activity: Further Comments 82
3.6. Notes on Mating and Communication in Insects 88
3.7. Rhythmicity in Tropical Insects . 100
3.8. Sociality and Defense in Social Insects . 104
3.9. Density-Related Behavior in Insects 111
3.10. Notes on the Physiology of Feeding in Insects 114
xi
xii CONTENTS
4. Ecological Aspects of Plant Defenses against Insects .137
4.1. Plant Defenses and Coevolution: An Overview. . . .. . 137
4.2. Evolution of Unpalatability and Implications for Food Chains 148
4.3. Notes on Defoliation in the Tropics . . . . . 158
4.4. Notes on Seed Predation in Tropical Habitats . 160
4.5. Notes on Plant-Ant Interactions in the Tropics. 164
5. Distribution Patterns of Insects in Tropical Habitats 173
5.1. The Concept of Local Adaptation . . . . . . 173
5.2. Examples of Habitat Differentiation in the Tropics 178
5.3. Insect Communities in Tropical Habitats . . . . 195
5.4. Plant Resources and Habitat Selection in Tropical Insects 201
5.5. Disturbed and Undisturbed Habitats: Some General Effects 207
6. Population Responses to the Environment in Tropical Insects 217
6.1. Adaptation to Habitats. . . . . . . . . . . . . . .. 217
6.2. Demography and Fitness in PopUlations: Implications for Tropical
Insects . . . . . . . . . . . . . . . . . . . 219
6.3. Further Notes on Population Regulation . . . . . . . .. 230
6.4. Some Examples of Census Histories in Tropical Insects . .. 239
6.5. Population Responses to Environmental Heterogeneity in Tropical
Insects . . . . . . . . . . . . . . . . . . . . .. 245
6.6. Competition as a Selective Force in PopUlation Responses .. 259
6.7. Spatial Environmental Heterogeneity and Demes in the Tropics 266
7. Effects of Seasonality on Insect Populations in the Tropics 273
7.1. Temperate Zone and Tropical Seasonality . . . . . 273
7.2. Some Regional Patterns of Seasonality in the Tropics 280
7.3. Some Seasonal Distributions of Tropical Insects . . 299
7.4. Molding of Ecological Traits in Tropical Insects by the
Dry Season . . . . . . . . . . . . . . . . . . 322
CONTENTS xiii
8. Dynamics of Organization of Insect Communities in Tropical
Ecosystems . . . . . . . . . . . . . . . . . . . . . 335
8.1. Notes on Tropical Ecosystems ............ 335
8.2. Patterns of Organization in Tropical Forests: Some Comments 337
8.3. Notes on the Dynamics of Tropical Insect Communities .. 341
8,4. Some Ecological Factors Generating Patchy Distributions of
Insects in Tropical Habitats . . . . . . . . . . . .. 375
9. Insect Species in Agricultural Habitats in the Tropics 387
9.1. Plant-Insect Interactions and Tropical Agricultural Habitats:
Some Comments . . . . . . . . . . . . . . . . .. 388
9.2. Insect Pollination in an Agricultural Habitat in the Tropics: The
Case of Cacao . . . . . . . . . . . . . . . . . .. 394
9.3. Grazing and Related Activities by Insects in Agricultural Habitats
in the Tropics ....... 405
9.4. Tropical Insect Pest Populations 420
10. Biogeographical and Regional Evolutionary-Ecological Effects on
the Maintenance of Tropical Insect Faunas: A Brief Perspective 429
10.1. Historical Events and Ecological Processes . . . . .. 429
10.2. Altitudinal and Other Macrogradients in Tropical Regions 435
10.3. Notes on Altitudinal Gradients in the Tropics . . . . .. 442
10.4 Biogeographical Patterns of the Origins of Tropical Insect Faunas 446
10.5. Some Mechanisms of Ecological and Evolutionary Differentiation 451
10.6. Some Examples of Differential Adaptation to Tropical Lowland
and Montane Areas by Insects . . . . . . . . . . . .. 455
References . . . . . . . . . . . . . . . . . . . . . . . . . 461
Index 495
