Pheromone Communication In Social Insects

Ants, Wasps, Bees, And Termites

Robert K Vander Meer, Michael D Breed, Mark Winston, Karl E Espelie

• Publisher: CRC Press
• Year: 2019
• Print ISBN:
  9780367282820
• eBook ISBN:
  9781000302363
• Topic: Biological Sciences
• Subtopic: Biology
• Index: Biological Sciences

Bringing together for the first time prominent researchers in social insect pheromone communication, including nestmate recognition, this book looks at ants, wasps, bees, and termites, highlighting areas of convergence and divergence among these groups, and identifying areas that need further investigation. Presenting broad synthetic overviews as well as species-specific studies, the volume will be useful to natural scientists, ecologists, and those interested in pest management, as well as to anyone interested in the fascinating chemically mediated behavioral interactions of social insects.

Part One
Introduction: Sources and Secretions

1
Pheromone Communication in Social Insects: Sources and Secretions

Johan Billen and E. David Morgan

Introduction

Although the general descriptions of insect anatomy and structure as found in entomological textbooks equally apply to social insects, the development of the exocrine apparatus in the latter clearly distinguishes them from solitary insects (Figure 1.1). An extremely diverse array of exocrine glands is found in all social insects, with 63 different glands described so far (39 if only considering the Formicidae, 21 for the Apidae, 14 for the Vespidae and 11 for the Isoptera) (Billen, 1994). Several of these glands serve 'individual' functions as the source of digestive enzymes or lubricant compounds, although the majority has a clear function related to the social organization of the colony (Hölldobler and Wilson, 1990). Some have a role in producing building material like the wax glands in bees, others secrete antibiotics like the metapleural glands of the ants, or elaborate sticky defensive substances like the frontal glands of some termite species. A major social function of exocrine glands, however, is the production of pheromones, for which many elands have become specialized.

The study of exocrine glands in general, and of pheromone producing glands in particular, has long been faced with a number of practical difficulties. Because of their ectodermal origin, all exocrine glands are associated with cuticle, which has put considerable constraints on the study of gland structure. The development of plastic embedding techniques has allowed much better sectioning conditions, which have resulted in a clearer picture of the structural organization of the exocrine system compared with the information obtained from paraffin sections. The small size of insects, on the other hand, for long represented a considerable drawback in our chemical understanding of the glandular secretions. The availability of more sophisticated equipment and techniques in the past decades has made analysis at the nanogram level possible, thus resulting in the identification of many glandular products. In this chapter, we focus on the structural and chemical complexity of the pheromone producing exocrine glands of the social insects.

FIGURE 1.1 Schematical profile drawings showing the commonly found exocrine glands in wasps, bees, ants and termites. Glands with a pheromonal function are indicated with capital lettering.

Structural Organization of Pheromone-Producing Glands

Exocrine glands can be classified into two major types according to the structural organization of their secretory cells (Billen, 1991), corresponding with types I and III in the pioneer paper on insect glands by Noirot and Quennedey (1974). Glands with secretory cells of the first type (type I) are directly derived from the tegumental epidermis as is reflected in their epithelial organization. The secretory cells form a monolayered epithelium either as part of the external body tegument through which they directly discharge their secretory products (e.g. the trail producing sternal glands of termites, Figure 1.2), or as the lining of an internalized reservoir where secretion can be temporarily stored (e.g. the postpharyngeal gland in ants, that is involved in recognition mechanisms, Figure 1.3).

More complicated are the glands with secretory cells of the second type (type III according to Noirot and Quennedey, 1974), where the gland is formed by a variable number of bicellular units, each comprising a secretory cell and a duct cell. Each unit of this gland type originates via tetrad formation by an epithelial stem cell through two mitoses, and subsequent differentiation of one daughter cell into a slender duct cell and one into the secretory cell, while the remaining two daughter cells degenerate (Sreng and Quennedey, 1976). The contact area between the remaining duct cell and secretory cell is known as the 'end apparatus', that represents a specialized region to allow secretory products to find their way to the outside. Glands of this type can equally open, by means of their duct cells, either directly through the tegument (e.g. the Van der Vecht gland in wasps, which is the source of repellent substances, Figure 1.4), or into a reservoir (e.g. the mandibular gland, which is the source of alarm substances in many social insects, Figures 1.5,1.6). The reservoir in these glands is formed bv flattened, generally non-secretory epithelial cells.

Secretory cells of type II were described as basally located epithelial cells without contact with the apical cuticle, as is sometimes found in sternal glands of termites (Noirot and Quennedey, 1974). They probably do not represent another secretory cell type, but are to be considered as oenocytes (Noirot and Quennedey, 1991).

Many glands are common to all social insects and occur in the queens, workers and males, as is for example the case for the mandibular and salivary glands. Apart from these standard exocrine glands that are also found in solitary insects, some glands represent neoformations that are characteristic for the family, subfamily, genus or even for the species. In this way, wax glands are characteristic for the Apidae, and are not found elsewhere. Likewise, Van der Vecht's gland and Richards' glands are specifically found in wasps, while ants are characterized by the presence of postpharyngeal, metapleural and pygidial glands. The exocrine glands of the heterometabolous termites cannot be homologized with the glands of the Hymenoptera, and therefore can be considered as rather specific.

The number of known exocrine glands in social insects becomes more and more impressive, and reflects the evolution of sectioning techniques. Several hitherto unknown glands have recently been described (Figure 1.7), although their function often still remains unknown so far. Because of this steadily increasing variety of exocrine

FIGURES 1.2-1.6 Semi-thin sections through various types of pheromone producing glands. 1.2 - epithelial glands directly opening through the tegument (sternal glands of the termite Schedorhinotermes lamanianus, scale bar 50 μπι); 1.3 - epithelial gland with reservoir (postpharyngeal gland of the ant Cataglyphis niger, scale bar 20 μιη); 1.4 - bicellular units opening directly through the tegument (Van der Vecht's gland of a worker of the wasp Polistes annularis. Also note associated epithelial gland, scale bar 20 μm); 1.5 - scanning micrograph showing the mandibular gland of a worker of the ant Formica sanguinea with bicellular units opening into common reservoir (scale bar 50 μπι); 1.6 - bicellular units opening into common reservoir (mandibular gland of a worker of the bumblebee Bombus pratorum, scale bar 50 μm). ct: cuticle, DC: duct cell, EA: end apparatus, GE:glandular epithelium, R reservoir, SC: secretory cell.

FIGURE 1.7 Examples of recently discovered "new" exocrine glands in the Formicidae (A. intramandibular gland; B. gemma gland Diacamma; C. coxal glands Pachycondyla; D. pretarsal glands; E. cloacal gland Cataglyphis; F. sting bulb gland Myrmecia and Nothomyrmecia). Scale bar 100 μm.

glands, a clear designation of the various glands is necessary. The terminology 'sternal glands', for instance, includes at least 6 different glands in the Formicidae, and also in the wasps, a plethora of glands associated with the abdominal sternites is found (Downing, 1991). Similarly, recent research has revealed the existence of a much broader variety of 'leg glands' than was originally thought.

Ultrastructure of Pheromone-Producing Glands

Glands are structures specialized for the storage and the emission, spreading or evaporation of their secretory products (Noirot and Quennedey, 1991). This implies the glandular cells display a specific capacity for the uptake of precursor molecules and the subsequent biosynthesis of the secretory products, and can effectively regulate the release of secretion.

Uptake of precursor substances in general is facilitated by the invaginations of the cell membrane that increase the surface. This is found for the basal cell membrane of the epithelial glands and the peripheral cell membrane of the secretory cells of the bicellular unit glands, which in both cases represent the area that is in contact with the haemolymph, from where precursor molecules are obtained. The cytoplasm of the secretory cells of pheromone producing glands is generally characterized by the presence of a well developed Golgi apparatus and smooth endoplasmic reticulum (Figs. 1.8,1.9). This is in agreement with the production of non-proteinaceous and low molecular weight substances, which are characteristic of many pheromone-producing glands (Noirot and Quennedey, 1974; Billen, 1991). Another common feature in the cytoplasm of pheromone producing glands is the occurrence of various inclusions, of which lamellated bodies are the most conspicuous (Figure 1.13). These probably correspond with secretory material, as may be concluded from autoradiography studies...

Table of contents

• Cover
• Half Title
• Title
• Copyright
• Contents
• Foreword
• Preface
• Acknowledgments
• PART ONE INTRODUCTION: SOURCES AND SECRETIONS
• PART TWO NESTMATE RECOGNITION IN SOCIAL INSECTS
• PART THREE SOCIAL INSECT RELEASER PHEROMONES
• PART FOUR SOCIAL INSECT PRIMER PHEROMONES
• List of Contributors
• Author Index
• Taxonomic Index
• Subject Index