Insect Morphology and Phylogeny

Foreword
This book emerged from a close cooperation between scientists from the Institute of
Zoology of the Chinese Academy of Sciences (CAS) and two German institutions, the
Institut für Spezielle Zoologie und Evolutionsbiologie mit Phyletischem Museum of
the Friedrich-Schiller-Universität Jena and the Biozentrum Grindel & Zoologisches
Museum of the University of Hamburg. Between these institutions, joint research projects have focused on insect anatomy and innovative morphological techniques and
on the phylogeny and evolutionary history of different hexapod lineages. Our progress and interest in these topics are reflected in the contents of this work.
The tremendous importance of Hexapoda was highlighted in numerous contributions and will not be treated in detail here. However, the most outstanding feature
of this clade is its unparalleled diversity. With approximately 1,000,000 described
species, they comprise more than half of the known total species diversity on this
planet. However, what is presently known is apparently only the tip of the iceberg.
Estimates of the real diversity range between 2 million species and a staggering
number of 30 million. Hexapod species often occur in extremely dense local populations and can form an immense biomass. Up to 100,000 springtails in only one m3
of
forest topsoil or millions of mosquitos forming gigantic swarms are only two examples of such incredible population density, among many others. Hexapods are largely
and primarily missing in marine habitats, but they play a crucial role in nearly all
terrestrial ecosystems and occur in a broad variety of limnic habitats. They have a
huge impact on human health as vectors of many diseases (e.g., malaria, sleeping
sickness), and many species are important plant pests or pests of stored products.
Positive aspects of hexapods include their role as predators or parasitoids of pest
species (mostly pest insects) and as pollinators of plants including important crops.
Insects are an important food source for numerous animal species and traditionally
also for humans in many parts of the world. Last but not least, the production of silk
and honey have been important economic factors going back several thousand years.
The combination of unusually complex morphology, fascinating biology, remarkable
species attractiveness and charisma, economic and medical impact, and various other
aspects have made hexapods a highly attractive group for researchers and dedicated
amateurs for centuries. Moreover, the grave threat posed by an unparalleled biodiversity crisis to the seemingly inexhaustible hexapod diversity presents one more very
serious reason to intensify the study and detailed documentation of this fascinating
group of organisms.
Insect morphology was a flourishing discipline in the first two thirds of the 20th
century, with outstanding researchers such as J. Chaudonneret and H. Weber in European countries, but also excellent entomologists in other parts of the world. Morphology based systematic entomology arguably reached a peak with the publication of
Willi Hennig’s groundbreaking work “Die Stammesgeschichte der Insekten” in 1969.
Towards the end of the 20th century, the detailed anatomical study of insects became
VIII  Foreword
less and less popular, a development apparently linked to the rise of molecular systematics. However, in the last ten years innovative techniques and new theoretical
concepts (e.g., “evolutionary morphology”) have led to a remarkable renaissance of
the investigation of structures and functions of Hexapoda.
Molecular systematics has “evolved” with breathtaking momentum in the last ten
years (see e.g., 1KITE.org). Robust “molecular phylogenies” will likely be available for
Hexapoda and other groups of organisms in the very near future. Nevertheless, morphology will continue to play a vital role for different reasons. First of all, it provides
an independent source of information for critically evaluating molecular trees (and
vice versa), a procedure referred to as the “model of reciprocal enlightenment” by
W. Hennig. Organisms cope with their environment using their morphological structures, which are the main target of natural selection. Body functions cannot be understood without solid morphological data, and detailed and meaningful evolutionary
scenarios cannot be developed without knowing the changes on the phenotypic level.
Another obvious reason is that morphology is the only source of information regarding fossils. To reconstruct the evolution of Hexapoda in its historical dimension is
only possible using morphological data for the placement of extinct taxa.
The primary purpose of this book is to provide a comprehensive overview of
hexapod morphology, mainly, but not exclusively, for investigations in an evolutionary context. On one hand an overwhelming richness of available data is made easily
accessible here, including also extensive and highly valuable sources in non-anglophone languages (see below). On the other hand, extensive results of our own morphological investigations are integrated in this volume, including comprehensive tables
of muscles with recently introduced nomenclatures, high quality SEM micrographs,
and computer-based 3D reconstructions. The second main aim is to outline the state
of the art in hexapod phylogenetics. The almost unprecedented progress in hexapod
systematics in the last years, arguably comparable to Hennig’s “Stammesgeschichte
der Insekten”, provides an almost ideal background. Long disputed questions, such
as the position of Strepsiptera (“the Strepsiptera problem”), are now settled, and it is
probably not overoptimistic to assume that a more or less completely resolved hexapod
phylogeny (on the interordinal level) will be available in the very near future. In this
context it should be emphasized that this is not only owed to the immense progress
in molecular systematics, but also to several coordinated morphology-based projects,
including phylogenetic studies of Polyneoptera and Holometabola.
The first main part of this book covers general hexapod morphology (1. Morphology) which is followed by a concise treatment of the development and immature
stages (2. Reproduction, development and immature stages) and an extensive
glossary (3. Glossary of hexapod morphology). A broad spectrum of traditional and
innovative morphological techniques is described briefly in the next chapter (4. Traditional and modern morphological techniques) followed by a brief introduction
into morphology-based phylogenetics (5. Phylogenetic reconstruction based on
morphology). The second main part (6. The hexapod orders) covers all currently
Foreword  IX
recognized hexapod orders and their systematic relationships. The main focus in the
ordinal chapters is on the morphology, but these chapters also contain shorter sections on the distribution and diversity, taxonomy, biology, reproduction, fossil record,
and economic importance of the different orders.
The information presented in this volume is based on numerous sources (see
7. Literature). Works extensively used are Snodgrass’ classical “Principles of Insect
Morphology”, the German “Handbook of Zoology” series (De Gruyter), the “Traité de
Zoologie” (edited by P.P. Grassé), some textbooks in German language (e.g., “Entomologisches Praktikum”, G. Seifert), and last but not least “Evolution of the Insects”
by D. Grimaldi and M. Engel. It should be emphasized that numerous specialists have
made valuable contributions to this volume by carefully reviewing chapters (see
Acknowledgements). Few chapters were written by invited specialists Assoc. Prof. Dr.
M. Bai (Chinese Academy of Sciences), Dr. B. Wipfler, and Dipl. Biol. K. Schneeberg
(Institut für Spezielle Zoologie und Evolutionsbiologie, University Jena).
This book addresses students of entomology, especially those interested in morphology, phylogeny and evolution, but also researches dealing with hexapod systematics or other aspects of entomology. A slightly modified Chinese version of this book
is presently in preparation. We hope that this contribution will not only promote the
study and investigation of insect morphology and evolution but also stimulate international exchange and joint research projects in systematic entomology and related
disciplines.
Rolf G. Beutel Si-Qin Ge
Frank Friedrich Xing-Ke Yang