The Insects has been the standard textbook in the field since the first edition published over forty years ago. Building on the strengths of Chapman's original text, this long-awaited 5th edition has been revised and expanded by a team of eminent insect physiologists, bringing it fully up-to-date for the molecular era. The chapters retain the successful structure of the earlier editions, focusing on particular functional systems rather than taxonomic groups and making it easy for students to delve into topics without extensive knowledge of taxonomy. The focus is on form and function, bringing together basic anatomy and physiology and examining how these relate to behaviour. This, combined with nearly 600 clear illustrations, provides a comprehensive understanding of how insects work. Now also featuring a richly illustrated prologue by George McGavin, this is an essential text for students, researchers and applied entomologists alike.

The insects: structure and function.

The functional morphology and biochemistry of insect male accessory glands and their secretions

The Insects by R. F. Chapman

Sexual selection is a major force driving the evolution of diverse reproductive traits. This evolutionary process is based on individual reproductive advantages that arise either through intrasexual competition or through intersexual choice and conflict. While classical studies of sexual selection focused mainly on differences in male mating success, more recent work has focused on the differences in paternity share that may arise through sperm competition or cryptic female choice whenever females mate with multiple males. Thus, an integrative view of sexual selection needs to encompass processes that occur not only before copulation (pre-mating), but also during copulation (peri-mating), as well as after copulation (post-mating), all of which can generate differences in reproductive success. By encompassing mechanisms of sexual selection across all of these sequential reproductive stages this review takes an integrative approach to sexual selection in Tribolium flour beetles (Coleoptera: Tenebrionidae), a particularly well-studied and economically important model organism. Tribolium flour beetles colonize patchily distributed grain stores, and juvenile and adult stages share the same food resources. Adults are highly promiscuous and female reproduction is distributed across an adult lifespan lasting approximately 1 year. While Tribolium males produce an aggregation pheromone that attracts both sexes, there appears to be little pre-mating discrimination among potential mates by either sex. However, recent work has revealed several peri-mating and post-mating mechanisms that determine how offspring paternity is apportioned among a female's mates. During mating, Tribolium females reject spermatophore transfer and limit sperm numbers transferred by males with low phenotypic quality. Although there is some conflicting evidence, male copulatory leg-rubbing appears to be associated with overcoming female resistance to insemination and does not influence a male's subsequent paternity share. Evidence suggests that Tribolium beetles have several possible post-mating mechanisms that they may use to bias paternity. Male sperm precedence has been extensively studied in Tribolium spp. and the related Tenebrio molitor, and several factors influencing male paternity share among a female's progeny have been identified. These include oviposition time, inter-mating interval, male strain/genotype, the mating regimen of a male's mother, male starvation, and tapeworm infection. Females exert muscular control over sperm storage, although there is no evidence to date that females use this to differentiate among mates. Females could also influence offspring paternity by re-mating with additional males, and T. castaneum females more readily accept spermatophores when they are re-mating with more attractive males. Additional work is needed to examine the possible roles played by both male and female accessory gland products in determining male paternity share. Sexual selection during pre-mating episodes may be reinforced or counteracted by peri- and post-copulatory selection, and antagonistic coevolution between the sexes may be played out across reproductive stages. In Tribolium, males' olfactory attractiveness is positively correlated with both insemination success and paternity share, suggesting consistent selection across different reproductive stages. Similar studies across sequential reproductive stages are needed in other taxa to provide a more integrative view of sexual selection.

An integrative view of sexual selection in Tribolium flour beetles.

The production of spermatozoa in the male insect and the transfer of the seminal mass to the female require significant investments of biochemical resources and the temporal coordination of development in several organs. Maturation of the gonads and the secondary reproductive systems must be synchronized with the metamorphic acquisition of energetic, sensory, motor, and central nervous adaptations for mating. The developmental hormones that commit cells to new programs and that trigger and modulate their expression in molting cycles also affect the primary and secondary reproductive systems. Many studies have addressed the endocrine regulation of female reproductive maturation and physiology. In comparison, investigations of the male insect systems have lagged. But in the past few years, more laboratories have focused their activities on analyses of male reproduction and its control (9, 57, 58). A recent chapter in this series reviewed the male accessory gland systems (9). This review discusses some of the recent studies that enlarge our knowl­ edge of the special physiology of the male. Selected examples summarize investigations that show that the major hormones that control growth and metamorphosis of the epidermis also control the growth, differentiation, and physiological modulation of the male reproductive system. In addition, male

Maturation of the Male Reproductive System and its Endocrine Regulation

The morphology of the bean-shaped accessory glands (BAGs) of males of Tenebrio molitor is described. All cells in the secretory epithelium are long and narrow (300-400 mμ × 5 mμ). The seven types of secretory cells are distinguished from one another by the morphology of their secretory granules. Granule substructure varies from simple spheres with homogeneous electrondense contents to complex forms with thickened exterior walls or with crystalline and membranous contents. Individual cell types were mapped by staining whole glands with Oil Red O, and the cell distributions were confirmed by wax histology and ultramicroscopy. The secretions of all seven cell types form a secretory plug composed of seven layers. During mating, the secretory plug from each BAG is forced into the ejaculatory duct by contractions of a sheath of circular muscle. The mirror image plugs from symmetrical BAGs fuse and are transformed into the wall of the spermatophore.

Cytodiffrentiation in the accessory glands of Tenebrio molitor. VI. A congruent map of cells and their secretions in the layered elastic product of the male bean-shaped gland.

The bean-shaped accessory glands of male mealworm beetles are morphologically complex. Seven distinct cell types produce a semisolid secretory mass that contains structural proteins of the spermatophore. Cell numbers increase 3.5-fold over the pupal instar, and gland volume increases 30-fold over the pupal and early adult stage. DNA content reaches its maximum at adult ecdysis (11 pg/secretory cell), RNA at 4 days later (55 pg/cell), and protein at 6 days after ecdysis (1,200 pg/cell). Rates of 14C- and 3H-leucine incroporation increase in parallel to the rise in protein content. Over ten putative secretory protein bands were identified by using one-dimensional SDS-slab gel electrophoresis to compare BAG homogenates with homogenates of the secretory mass and the spermatophore. At least five of these secretory proteins accumulate in BAGs after adult ecdysis, and most show high rates of leucine incorporation in the adult. Twodimensional gel electrophoresis (pI and SDS) and fluorography allowed us to identify a score of reference spots, at least seven spots that are characteristic of the pupa, and over 40 spots that appear to be differentiation-specific and are presumably secretory products. The fluorographic indices give an unambiguous means of scoring terminal differentiation in the BAG.

Cytodifferentiation in the accessory glands of Tenebrio molitor. VII. Patterns of leucine incorporation by the bean‐shaped glands of males

The bean-shaped accessory glands of male Tenebrio consist of a single-layered epithelium which is surrounded by a muscular coat. The epithelial layer, which produces precursors of the wall of the spermatophore, contains eight secretory cell types. Each secretory cell type is in one or more homogenous patches, and discharges granules which form one layer of the eight-layered secretory plug. Maturation begins in cell types 4, 7, and 6 on the last pupal day. A newly identified cell (type 8) in the posterolateral epithelium matures last. Cells of individual types mature in synchrony, and their secretory granules "ripen" in a sequence that is characteristic for each type. As the secretory cells of each patch mature, unusual short-lived cells appear at interfaces between patches. In some cases the secretory granules in these boundary cells have ultrastructural features which are mixtures of the definitive characteristics of granules in adjacent cell types. The transitional cell types disappear at 3-4 days after eclosion. Intermediate cell types are absent in the mature gland and boundaries between the patches are distinct. The transitional cells may form granules of intermediate structural characteristics as a dual response to cellular interaction with adjacent and previously differentiated secretory cells.

Cytodifferentiation in the accessory glands of Tenebrio molitor. XI. Transitional cell types during establishment of pattern

The aedeagal gland of male Tenebrio molitor consists of numerous acini containing several secretory units (organules) of three epithelial cells in series. The distal cortical cell and intermediate cell are secretory cells. Secretory products are passed into microvilli-lined extracellular reservoirs. From these storage areas products flow through minute canaliculi and into the efferent ductule. Canaliculi, cuticular trabeculae, and fibrillar material are characteristic features of the efferent ductules within the extracellular reservoirs of secretory cells. After passing from the secretory cells, the efferent ductule penetrates the basal ductule cell. The thin epicuticle that comprises the wall of the ductule is confluent with the epicuticle of the cuticular sheath forming the wall of the genital pocket. Secretory products flow from the cortical cell ductule into the intermediate cell and eventually empty into the genital pocket. A chemical reaction apparently takes place in the intermediate cell ductule, resulting in a frothy secretion product. When released from the ductule, this frothy product forms a foam-like layer that coats the inner wall of the genital pocket. Ultrastructural and probable functional aspects of this gland are described and discussed.

Patrick J. Dailey

Papers

Cytodiffrentiation in the accessory glands of Tenebrio molitor. VI. A congruent map of cells and their secretions in the layered elastic product of the male bean-shaped gland.

Cytodifferentiation in the accessory glands of Tenebrio molitor. VII. Patterns of leucine incorporation by the bean‐shaped glands of males

Cytodifferentiation in the accessory glands of Tenebrio molitor. XI. Transitional cell types during establishment of pattern

Morphology of the aedeagal gland of the male mealworm beetle (Tenebrio molitor L.).