André Quennedey

Innervation de type neurosécréteur dans la glande sternale de Kalotermes flavicollis (Isoptera). Étude ultrastructurale

The sternal gland of Kalotermes flavicollis secretes a trail pheromone dissolved in a lipid substance. The gland appears as an epidermal thickening in the anterior part of the fifth abdominal sternite. Two types of cells may be recognized: glandular cells with many lipidic droplets and columnar cells with a brush border beneath the cuticle. There are also about thirty campaniform sensilla. An ultrastructural study discloses nervous efferent fibres in the anterior part of the sternal gland. These fibres are easily distinguished from the sensory fibres by the following features: glial cells, which surround the axon before reaching the gland, end in the connective layer, and naked axons run between the gland cells to the base of the brush border. In the axoplasm there are electrondense granules (probably neurosecretory), 900 to 1500 A in diameter. Both at the level of the connective layer and in the gland near the columnar cells, ‘synaptoid vesicles’ are aggregated close to the axon membrane in ‘synaptoid areas’ where the neurotransmitter may be released. Such a ‘neurosecretomotor junction’ probably plays a role in the control of secretion. It is tentatively suggested that efferent nerve fibres influence the release of pheromene. Then the pheromone is mixed with the continuously produced lipid component before being laid down on the ground.

Postembryonic Development of Zophobas atratus Fab. (Coleoptera: Tenebrionidae) under Crowded or Isolated Conditions and Effects of Juvenile Hormone Analogue Applications

Abstract Pupation in Zophobas atratus is dependent on isolation and this provides a model for study of the onset of metamorphosis in beetles. We have analyzed the effects of isolation vs grouping on certain developmental parameters; the number of larval instars; their duration and weight. Sex differences were detected, such as the occurrence of regressive moults in females. Moreover, the development of Z. atratus is discussed in relation to Tenebrio molitor , the physiological timing of which appeared in part extendable to Z. atratus . Experiments show that 4–6 days of isolation are required for commencement of metamorphosis, as indicated by an immobile crooked posture observed at the end of this period, characterizing the beginning of prepupal development. During this period, return to grouped conditions, as well as applications of a juvenile hormone analogue (ZR 515) prevented metamorphosis and precipitated another larval moult. This suggests that grouped conditions may delay the onset of metamorphosis through the modulation of juvenile hormone titres.

Les glandes mandibulaires de Blaberus craniifer burm. (Dictyoptera, blaberidae) developpement, structure et fonctionnement

Abstract The mandibular glands of Blaberus craniifer are examined by histochemical, electrophoretic, thin-layer chromatography and electron microscopical techniques. These glands are known to secrete a volatile aggregative pheromone. The gregarious behaviour increases during insect development and is maximal in imagos. Each gland is composed of a bundle of secretory cells with efferent ductules which arise in a common duct. Secretory cells contain a myeloid secretion more abundant in imagos than in larval stages. Histochemical and electrophoretic criteria show that the myeloid product is made up of a mixture of glycoproteins. A lipidic component is also present in the secretion; its ultrastructural localization remains to be elucidated. Cytological features are in agreement with the gregarious behaviour of cockroaches. Detailed structure and functional interpretation are also discussed.

The fine structural organization of sternal glands of pseudergates and workers in termites (Isoptera) : A comparative survey

Thirty-nine species belonging to different families of termites are studied to give a comprehensive view of the evolution of the sternal glands. Several modifications occurring at cuticular and cytological levels are described in neuter castes. The outer epicuticle is always pierced by epicuticular pores. In advanced termites the epicuticular filaments greatly increase in number and length creating a thick layer. The pore canals gradually enlarge while the cuticle changes into a lattice structure lining an extracellular space in which the secretion is stored. Two classes of cells are present in basal termites (Mastotermitidae, Hodotermitidae, Termopsidae and Kalotermitidae) but their glandular structures greatly differ between families. A more complex organization with three classes of cells is found in the Serritermitidae and Rhinotermitidae. A regressive evolution occurs in the Termitidae where only two classes of cells are present. A dual nervous control (campaniform sensilla and neurosecretory fibers) is found in lower termites, except for the Hodotermitidae which have mechanosensory bristles. In the other families, neurosecretory fibers are lacking. A comparison with phylogenetic data is given. A more versatile role of sternal glands in neuter castes is hypothesized.

2-Deoxyecdysone is a circulating ecdysteroid in the beetle Zophobas atratus.

A qualitative analysis of ecdysteroids has been performed during the post-embryonic development of the tenebrionid beetle, Zophobas atratus, by high performance liquid chromatography (HPLC) combined with enzyme immunoassay (EIA) using two different antibodies. Three HPLC peaks were found to be immunoreactive, in hemolymph extracts of both sexes. Moreover, these peaks had ecdysteroid-like UV spectra, determined using a photodiode array detector. The use of two different HPLC systems (reverse and normal phases), in combination with two different EIA antibodies, allowed us to identify 20-hydroxyecdysone (20E) and ecdysone (E), as the two main ecdysteroids, but also suggested the presence of 2-deoxyecdysone (2dE) as the third hemolymph component. Secretion of putative 2dE, together with E (but not 20E) was also demonstrated in vitro from incubations of prothoracic glands and of tegumental explants. In these experiments, either in vivo or in vitro, 3-dehydroecdysone was never observed. Our observations thus strongly suggest that 2dE is a circulating ecdysteroid in Z. atratus and may function as a prohormone during the development of some insects.

Morphology and ultrastructure of paired prototergal glands in the adult rove beetle Philonthus varians (Coleoptera, Staphylinidae)

Philonthus and other genera of Philonthina possess a pair of prototergal glands located in the first abdominal tergum and hidden at rest by hind wings and elytra. In Philonthus varians they occupy the whole length of the tergum and form a pouch-like invaginated reservoir with a scaly glandular zone and a smooth outlet. A grille of long setae covers the opening of each gland. The fine structure of these glands is given for the first time. Three types of cells are found in the glandular epithelium. Epidermal cells underlie the cuticular scales, numerous class 1 secretory cells open in the centre of calyces made of finger-like processes of the cuticle, and class 3 cells are connected to pored tubercles. A cytological comparison is made with the diverse class 1 cells described to date in Coleoptera. In these cells different evolutionary trends are shown in the structure of the cuticular apparatus, particularly in the number, size and position of the cuticular apertures as well as in the length and abundance of epicuticular filaments. A possible defensive function of the prototergal glands against pathogens and their interest for the phylogenetic study of Staphylininae are discussed.

Ecdysteroid titres in a tenebrionid beetle, Zophobas atratus: effects of grouping and isolation.

Metamorphosis in Zophobas atratus is dependent on isolation: when kept in grouped conditions, larvae undergo numerous supernumerary moults, growing in size, without pupating. This beetle thus represents an interesting model for the analysis of possible differences in the endocrine regulation of normal vs. supernumerary larval moults. In this study, the ecdysteroid titres have been analysed in this species, using enzyme immunoassay. The hormonal variations of larvae undergoing normal or supernumerary larval cycles were particularly examined, in either grouped or isolated conditions. Normal larval cycles presented very similar ecdysteroid variations in grouped as well as isolated conditions, showing a single hormonal peak (at about 1000pg/&mgr;l). Supplementary larval cycles, occurring in grouped conditions, also showed a similar single ecdysteroid peak, but after a longer period of basal levels. Isolation of such larvae triggered their larval-pupal transformation, which was characterized by more complex hormonal fluctuations, including a small ecdysteroid peak before the main one. Interestingly, the isolation of big larvae during a large part of their cycle induced this peculiar hormonal pattern synchronously, confirming the involvement of a complex neuroendocrine control between external conditions and ecdysteroid titres.

Development of the wing discs of Zophobas atratus under natural and experimental conditions: occurrence of a gradual larval-pupal commitment in the epidermis of tenebrionid beetles

Abstract Using light and electron microscopy, we studied the development of the wing discs in the large beetle Zophobas atratus, under natural and experimental conditions. A reversible differentiation of the wing discs is usually observed during supernumerary instars of crowded larvae. Juvenile hormone analog (JHA) application during the wandering period or compelled experimental crowding during the larval-pupal switchover – or commitment – inhibits the onset of metamorphosis. Isolation, followed by recrowding, also induces the disc cells to secrete unusual cuticular material. Recrowding is able to trigger the reversal of metamorphosis during the 4-day period when larval-pupal commitment is taking place. Likewise, feeding behaviour which normally stops at commitment often recovers. Ecdysis of intermediate instar animals (prothetelic larvae) corroborates the occurrence of a temporal and spatial variation to commitment, unique to each organ. All these data lead us to consider this 4-day period, which we have called the C period or commitment period, extending from the wandering stage (the previous T period) to the crooked posture stage (i.e. from eyestage 4 to 7) as the physiological time during which the larval organs are gradually committed to differentiate into pupal organs.

The precocious commitment of wing Anlagen in Tenebrio molitor revealed by the addition of 20-hydroxyecdysone.

An injection of 20-hydroxyecdysone (10 mug per animal) 6-13 days after the moult of the last larval instar of Tenebrio molitor induces the development of prothetelic larvae and larval-pupal intermediates. The state of larval-pupal switchover, or commitment, is only disclosed at the time of injection of the moulting hormone. Prothetelic A and B larvae, with small and medium sized wing Anlagen, undergo another larval or pupal instar. Prothetelic C larvae with bigger Anlagen are unable to moult, but the adult programme is expressed. Ecdysed larval-pupal intermediates give more or less perfect adults, while unecdysed mealworms, imprisoned in their larval cuticle, also expressed the adult programme. The commitment of Tenebrio is not a global switchover because a significant asynchronisation is noted between the development of organs considered. Animal crowding induces a delay in the appearance of wing Anlagen.