George M. Happ

Fine structure of the pygidial glands of Bledius mandibularis (Coleoptera: Staphylinidae).

Abstract The pygidial glands of B. mandibularis produce a mixture of terpenes, fatty acid derivatives, and a benzoquinone. The morphology of these glands is described with particular attention to the ultrastructure of the secretory cells and their efferent ductules. Each functional secretory unit consists of two secretory cells (cortical and medullary) both of which are associated with a common extracellular cuticular ductule. The fenestrated tip of the ductule lies in a cavity bounded by the invaginated plasma membrane of the cortical cell; within the cavity surrounded by the medullary cell, the ductule is divided into a bulb region (where a spherical mass of fine cylinders surrounds the ductule itself) and an unfenestrated switchback region. Inflated cisternae of rough endoplasmic reticulum, filled with flocculent material of low electron density, are abundant in the cortical cytoplasm, and presumably represent primary secretory product en route to the cavity of this cell. The plasma membrane bounding this cavity is much infolded, and the inner surface of this membrane is studded with fine particles. In contrast, few cisternae are inflated in the medullary cell and the corresponding infolded plasma membrane is smooth. The manner in which both cells may cooperate to produce the heterogeneous secretory product is discussed.

Fine structure of the spermatheca of the mealworm beetle (Tenebrio molitor L.)

SummaryThe spermatheca of the female mealworm beetle is an inflorescence of branching cuticular ducts which is connected to the bursa copulatrix via a cuticular neck surrounded by a muscular coat. The infolded bursal cuticle consists of a distinct outer epicuticle, inner epicuticle, procuticle, and a subcuticular zone; the latter is rich in mucopolysaccharides. The cuticle of the neck lacks a distinct procuticle. The cuticle of the spermatheca itself is mostly inner epicuticle with two thin underlying lamellae of procuticle. The cells of the bursa are loosely coupled to the procuticle, whereas cuticular projections bind the epithelia of the “neck” and the spermatheca proper to the underlying epithelia. The apical plasma membranes of the spermathecal epithelium are sinuous and much infolded; we believe that this epithelium controls the micro-environment within the cuticular ducts.

Cytodifferentiation in the accessory glands of Tenebrio molitor. III. Fine structure of the spermathecal accessory gland in the pupa.

To establish indices for studying the hormonal control of differentiation of the accessory reproductive glands of insects, the ultrastructural development of the spermathecal accessory gland (SAG) of female mealworm beetles has been analyzed. Over the 9 days between adult and pupal ecdysis, the SAG transforms from a stubby sac of columnar epithelium into an elongate cylindrical gland, lined with cuticle, and containing several distinct types of differentiated cells. The first phase of pupal differentiation is one of cell division and overall gland morphogenesis which lasts 3--4 days; at its close, two populations of cells can be distinguished. One of these populations will produce the cuticular ductules while the other will yield the three-cell secretory units or organules. In the second phase which lasts 2 days, the three cells of each organule become wrapped around one another and then the innermost puts out a pseudocilium and retracts within the next ensheathing cell. In the third phase which lasts 4 days, the cuticles of the axial duct, of the efferent ductule, of the vestibule upon which the ductules converge, and of the end apparatus, are deposited. The ciliary process degenerates, and after ecdysis, the secretory cells undergo peak differentiation.

Fine structure of the bean-shaped accessory gland in the male pupa of Tenebrio molitor L. (Coleoptera : Tenebrionidae)

Abstract The bean-shaped accessory glands of the mealworm beetle, Tenebrio molitor L., produce secretions that form the outer layers of the spermatophore. We aim to understand the hormonal control of growth and differentiation of these glands. In the present paper, we describe the morphology of the glands during pupal maturation in situ . The primary ultrastructural changes during development are those related to the maturation of the secretory machinery, including an increase in prominence of the nucleoli, the expansion of the rough endoplasmic reticulum and Golgi complexes, and tracheolar invaginations into the glandular epithelium. These glands increase in size due to cell division, and undergo a change in shape from oval to reniform due to differential mitotic rates in different regions. Of particular interest are cytoplasmic bridges between apposed cells. Although most common during the peak period of cell division, these bridges are not merely relics of incomplete cytokinesis but are potential sites for inter-cellular communication. The study has provided useful indices for scoring the progressive differentiation of the bean-shaped glands.

Ultrastructure of the mesonotal mycangium of an ambrosia beetle, Xyleborus Dispar (F.) (Coleoptera: scolytidae)☆

Abstract Fungal symbionts of the ambrosia beetle, Xyleborus dispar, are transported within a glandular invagination of the body cuticle, termed the mycangium. The associated secretory cells pass their products into the mycangium via efferent cuticular ductules. Hemidesmosomes on microvilli apparently anchor the end apparatus of each ductule in the compartment. The fungal propaguXles within the mycangium are of 2 types: a small-celled fungus which is apparently the classical ectosymbiont, Ambrosiella hartigii, and a large, multinucleate propagule, which is a yeast-like basidiomycetous derivative.

Patterns of leucine incorporation in the spermathecal accessory glands of the post-ecdysial adult female Tenebrio molitor

Abstract The spermathecal accessory glands of female mealworm beetles become fully active by six days after pupal-adult ecdysis. Coincident with the morphological maturation, increases occur in protein and RNA content and in total leucine incorporation. Three classes of differentiation-specific proteins are increasingly prominent and show heightened rates of leucine incorporation by the sixth day.

Neuroendocrine control of moulting cycle in mealworms: Histology and autoradiography of cephalic components

Abstract Fluctuations in the activities of the cephalic neuroendocrine system of larval mealworms ( Tenebrio molitor ) have been investigated by autoradiographic and histological techniques. Shortly after ecdysis, the proteinaceous granules in the cytoplasm of the ‘A’ type medial neurosecretory cells of the brain undergo a marked increase in numbers per cell and in chromophilia; both numbers and stain density reach a maximum about two-thirds of the way through interval between ecdyses and then both decline precipitously. The cyclic histological changes are nicely correlated with overall patterns of protein synthesis, as demonstrated by incorporation of 3 H-amino acids into the medial cells. Paradoxically no cyclicity was observed downstream: no fluctuations in numbers or chromophilia of stainable inclusions were detected in the axons of the medial neurosecretory cells, in the corresponding efferent nerves to the corpora cardiaca, or within the cardiaca themselves. Mechanisms are proposed to account for this apparent paradox, and the patterns of protein synthesis within the ‘A’ type medial neurosecretory cells are correlated with previously determined fluctuations in moulting hormone activity.