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PHYSIOLOGICAL SYSTEMS IN INSECTS This page intentionally left blank PHYSIOLOGICAL SYSTEMS IN INSECTS FOURTH EDITION Marc J. Klowden Professor Emeritus of Entomology, University of Idaho, Moscow, ID, United States Subba Reddy Palli University Research Professor and Chair, Department of Entomology, College of Agriculture, Food and Environment, University of Kentucky, Lexington, KY, United States Academic Press is an imprint of Elsevier 125 London Wall, London EC2Y 5AS, United Kingdom 525 B Street, Suite 1650, San Diego, CA 92101, United States 50 Hampshire Street, 5th Floor, Cambridge, MA 02139, United States The Boulevard, Langford Lane, Kidlington, Oxford OX5 1GB, United Kingdom Copyright © 2023 Elsevier Inc. All rights reserved. No part of this publication may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. 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To the fullest extent of the law, neither the Publisher nor the authors, contributors, or editors, assume any liability for any injury and/or damage to persons or property as a matter of products liability, negligence or otherwise, or from any use or operation of any methods, products, instructions, or ideas contained in the material herein. ISBN 978-0-12-820359-0 For information on all Academic Press publications visit our website at https://www.elsevier.com/books-and-journals Publisher: Charlotte Cockle Acquisitions Editor: Anna Valutkevich Editorial Project Manager: Charlotte Cockle Production Project Manager: Sreejith Viswanathan Cover Designer: Mark Rogers Typeset by STRAIVE, India Contents Preface to the Fourth Edition vii 4. Reproductive systems 1. Signaling systems Female reproductive systems 190 Vitellogenesis 198 Paracrine signaling 4 Ovulation, fertilization, and oviposition 208 Endocrine signaling 8 Male reproductive systems 210 Types of hormone release sites in insects 10 Unconventional methods of insect Early experiments that set the stage for our current reproduction 222 understanding 11 Mating systems 228 Type of hormones in insects 13 References of interest 231 Prothoracicotropic hormone 19 Ecdysteroids 25 5. Behavioral systems The juvenile hormones 42 Other neuropeptides found in insects 57 Ways of looking at behavior 248 Vertebrate-type hormones in insects 58 Genetic basis of insect behavior 250 References of interest 60 Hormonal regulation of behavior 253 Physiology of learning and memory 256 2. Integumentary systems Physiology of circadian rhythms 260 Physiology of polyphenisms 265 Insect growth and development 88 Physiology of temporal polyethisms 268 Instars, stadia, and hidden phases 92 Physiology of behaviors accompanying Structure of the integument 93 metamorphosis 269 Modified features of the integument 98 Physiology of eclosion behaviors 272 Chemistry of the cuticle 101 Behavioral modulation by parasites 275 The molting process 110 References of interest 277 Eclosion behavior and its regulation 112 Sclerotization 113 6. Metabolic systems Endocrine control of molting and metamorphosis 115 The insect alimentary tract 297 Signaling in cell and tissue growth 120 Metabolic processes in insects 317 Metamorphosis and the radically changing Metabolism of carbohydrates 321 cuticle 122 Metabolism of proteins 327 References of interest 130 Metabolism of lipids 331 Diapause as a metabolic process 338 3. Developmental systems References of interest 341 Morphogens and developmental patterns 143 7. Circulatory systems Insect eggs 145 Embryonic development 155 Structure of the insect circulatory system 360 References of interest 175 Immune mechanisms in insects 376 v vi Contents The circulatory system and temperature variations 388 11. Nervous systems References of interest 394 The nervous system as a key to the evolution of 8. Excretory systems arthropods 527 Basic components of the insect nervous Major excretory products in insects 409 system 529 Excretory organs 416 Maintenance of electrical potential and nervous Mechanism of Malpighian tubule secretion 419 transmission 533 Hindgut and rectum 422 Structure of the nervous system 538 Cryptonephridial system 423 Sensing the environment 544 Filter chamber 424 Mechanoreceptors 556 Hormonal control of excretion and Compound eyes 570 osmoregulation 425 Superposition eyes and adaptations for dim Storage excretion 428 light 577 Other functions of the Malpighian tubules 429 Visual pigments 579 References of interest 430 Perception of polarized light 581 Insecticides targeting the nervous system 584 9. Respiratory systems References of interest 587 Supplying cells with oxygen 439 12. Communication systems The tracheal system 442 Modifications that increase oxygen uptake 450 Visual communication 608 Nonrespiratory functions of tracheal systems 452 Acoustical communication 614 Discontinuous gas exchange 453 Tactile communication 620 Aquatic respiration 455 Chemical communication 621 References of interest 463 The multicomponent nature of bee communication 639 10. Locomotor systems References of interest 640 Basic structure of insect muscles 471 13. Genetics, genomics, and epigenetics Actin, myosin, and muscle activation 477 Types of skeletal muscles 481 Genetics 655 Basic structure of the insect wing 494 Genomics 663 Muscles involved in wing movements 496 Epigenetics 669 Wing movements during flight 498 References of interest 675 Wing coupling and control mechanisms 501 Flight muscle metabolism 502 Glossary 681 Terrestrial locomotion 508 References of interest 516 Index 695 Preface to the Fourth Edition Sir Vincent Wigglesworth, the prescient we knew that insects were different enough founder of the field of insect physiology, in- to survive the inevitable nuclear holocaust troduced his 1934 treatise, Insect Physiology, and repopulate the planet without us. The with the comment, “The fundamental pro- major reason to study insects was to find cesses of vital activity, the ordered series of new ways to kill them that didn’t kill us. physical and chemical changes which lib- In 1948, Wigglesworth presented a erate energy and maintain the ‘immanent well-documented justification for using movement’ of life, are probably the same insects as models for studying general ani- wherever ‘living matter’ exists.” In the 134 mal physiology. However, insects were still pages that followed in this first insect phys- largely relegated to the category of pests we iology textbook, Wigglesworth described aim to tolerate or eradicate. Through five what was known about the systems of in- editions of the classic Destructive and Useful sects based on what he estimated to be 2000 Insects, the value of insects to humans was publications. Despite his prophetic introduc- summarized in a short chapter, while their tion, few related comparisons of insect sys- destructive side dominated the remainder. tems followed in the little book, most likely Ten examples of how insects were beneficial because there were no comparisons to make or useful to humans were discussed, with since few others considered there to be much the last being the limited use of insects and in common between arthropods and ver- insect products in medicine. This included tebrates. The experiments by Kopeć (1922) maggot therapy for the treatment of wounds, demonstrating that the insect brain was a the use of insect venoms for treating rheu- source of hormones were largely ignored matism and arthritis, and the use of insect until Wigglesworth rediscovered them. Who extracts and products such as royal jelly as besides another insect physiologist would medicines. However, over the past 20 years, believe that these simple creatures had hor- there has been an unprecedented explosion mones, let alone hormones produced by an of information as molecular techniques insect brain the size of a poppy seed? The pi- have yielded information unobtainable by oneering work by Berta and Ernst Scharrer conventional biochemistry and physiology (1944) made a strong case for neurosecretion alone. Now that the genomes of humans and in both insects and vertebrates, but they too many species of insects can be compared, the had difficulty with the scientific community similarities are truly remarkable and empha- accepting the concept that nerve cells in any size the wisdom of Wigglesworth’s remarks animal could produce hormones. Insects in 1934. Given that the arthropod lineage were evolutionarily distant from humans, diverged from that of vertebrates more than classified in a primitive phylum, with a 600 million years ago, parallels between the strange basic body groundplan and physi- physiological systems of insects and humans ological makeup. During the cold war with are enough to make your respiratory system the policy of mutually assured destruction, inspire, give your integument chills, and vii viii Preface to the Fourth Edition cause your tarsi to twitch. It appears that as Ignoring the possibilities of consciousness many as 75% of the genes that are associated and personality, the far less complex insect with human genetic diseases have homolo- nervous system shares numerous similarities gies in Drosophila melanogaster. These similar- with that of humans. Insects may not dream, ities have altered the focus of insect science, but they certainly sleep. They meet the criteria with insects viewed more as model systems established for sleep: a period of quiescence for studying human physiology and a better that is associated with a species-specific pos- understanding of them able to be applied to ture, a reduced responsiveness to external ourselves to advance the pace of human dis- stimuli, a rapid reversibility to wakefulness, ease research. a homeostasis based on a longer recovery A reason often given for using insects in period following periods of sleep depriva- research is that they are simple. With few tion, and an appropriate expression of clock parts, moving or otherwise, an insect system genes. D. melanogaster engages in periods of can be studied without the complications of quiescence that are characterized by changes ancillary and redundant components and in brain activity and the specific expression is therefore much easier to dissect and ma- of numerous genes. Dozing flies undergo nipulate. The D. melanogaster genome, on its sustained periods of quiescence during the four pairs of chromosomes, is encoded by night but when prevented from sleeping are about 14,000 genes, a bit more than half of less adept at performing their usual tasks. the protein coding sequences identified in Just as older humans sometimes have prob- humans. Although each group has evolved lems sleeping, old flies show disturbances its own distinctive genes, many of those re- in their sleep patterns. Although total sleep lated to major biological processes have been amounts do not decrease in older D. melan- well conserved. The other obvious aspects ogaster, their sleep/wake cycles tend to be of short life cycles, little space required for more fragmented with age. The observation rearing, considerably less food needed than that the roundworm, Caenorhabditis elegans, if one were working with elephants, and the also sleeps indicates that sleep is a basic bio- advantage of being completely off the radar logical phenomenon common to many living screens of university animal care and use things and that D. melanogaster can be effec- committees, are additional points in their tive models for studying aging and sleep favor. Unfortunately, this view of simplicity in humans, and even the phenomenon of often tends toward a pejorative label; insects sleep-related restless leg syndrome. are small, are unsophisticated, and have lit- Several human neurodegenerative dis- tle in common with us more complicated eases, including Alzheimer’s disease, vertebrates. However, their size belies their Parkinson’s disease, muscular dystrophy, complexity, because their incredible success and Huntington’s disease, lack effective has not been in spite of their simplicity but treatments and have undetermined causes. because of it. To downplay this simplic- Given the identification of several homol- ity is also to conclude that an IBM system ogous regulatory genes involved in brain 360 computer that once filled an entire air- development in both humans and D. mela- conditioned room accompanied by a colossal nogaster, the use of insects to examine the 8 megabytes of storage was more complex genetic dissection of the developing brain than a present-day iPhone with 512 giga- may expand our knowledge of how gene bytes of memory that fits in your pocket. mis-expression or loss of function might be Preface to the Fourth Edition ix countered. The presence of the D. melanogas- insulin for both humans and insects in the ter homolog of the microtubule-associated sensing of nutritional state and triglycer- protein that is related to Alzheimer’s disease ide storage, controlling cell and organ size, could establish insects as suitable models and determining overall longevity make in- for Alzheimer’s. The kynurenine pathway sects ideal model systems for understanding for the degradation of the amino acid tryp- growth-related processes in vertebrates. The tophan has been studied in transgenic flies steroid insect hormone 20-hydroxyecdysone as a model for the treatment of Huntington’s (20E) that initiates molting of the exoskeleton disease. may also benefit the vertebrate skeleton as Because insects do not have vertebrate- an antiosteoporosis drug. Rats fed 20E over type breathing organs and, except for the 3 months showed increases in bone mineral largest insects, appear to be free from having density over controls. Rats also benefited to take the deep breaths that we do, Aristotle, from increases in the cross-sectional area of without the benefit of today’s scientific in- muscles after ingesting 20E isolated from strumentation in the ancient Greece of 350 plant material. In neither case were any side BC, can be forgiven for characterizing them effects noted. as animals that didn’t breathe. It is thus sat- An immunity to intestinal disease is es- isfying that the branching morphogenesis of sential given the widespread exposure of in- the developing insect tracheal system is now sects to microbial organisms acquired while recognized as a paradigm for the develop- feeding on fermenting substrates. There ment of branching in mammalian lung and are many similarities to the human intesti- vascular systems. D. melanogaster has also nal mucosa that involve both physical and been proposed as a model system for the molecular mechanisms that maintain a res- study of asthma-susceptibility genes and the ident flora and discourage pathogenic bac- innate immune responses of airway epithe- teria. Modeling human intestinal disease in lial cells, perhaps even more useful than the D. melanogaster has been proposed as many traditional mouse model. signaling pathways that regulate disease, as Given the health concerns about increases well as gut development and regeneration, in our waistlines, D. melanogaster metabolism have been conserved in human and insect and energy homeostasis may yield insights systems. Knowledge of the role of gut mi- into human obesity and the related pathol- crobiota in the regulation of overall human ogies such as diabetes. In mammals, insulin health and multiple physiological processes, and leptin signaling to centers in the brain including the social dysfunction associated regulate our metabolism and food intake. with autism-spectrum disorders and the Insulin has been recognized in insects for etiologies of Parkinson’s and Alzheimer’s many years, but it is only recently that the diseases, has increased dramatically in re- role of insulin signaling has been shown to be cent years. Neurophysiological effects of gut phylogenetically conserved. Although a nat- microbiota on the olfaction, communication, ural epidemic of obesity in the insect popula- and behavior of social insects parallel and tion has yet to be identified, transgenic flies could model the gut microbiota–brain con- with certain blocked neurons store more fat nection in humans. and suggest that the insect brain measures The tools of molecular biology have pro- the level of fat stores by similar mechanisms vided incredible insights into the physiolog- as does our own. The physiological roles of ical systems that contribute to the success of