The sperm ultrastructure and spermiogenesis of Tribolium castaneum (Coleoptera: Tenebrionidae) with evidence of cyst degeneration.

Previous studies on the spermatogenesis of tenebrionid beetles showed the unusual formation of two antiparallel sperm bundles per cyst. In this work we reported this feature also in Tribolium castaneum using light and transmission electron microscopy. The sperm structure of T. castaneum, similar to other tenebrionids, consists of a three-layered acrosome, an elongated nucleus and a flagellum with a 9+9+2 axoneme, two accessory bodies and two asymmetric mitochondrial derivatives. The presence of two antiparallel sperm bundles per cyst also in Meloidae and Rhipiphoridae suggests that it is a strong trait synapomorphic for Tenebrionoidea. The huge degeneration of whole sperm cells in several cysts of testes during spermiogenesis is also described.

The skeletomuscular system of the larva of Drosophila melanogaster (Drosophilidae, Diptera): a contribution to the morphology of a model organism.

The morphological features of the third instar larva of the most important insect model, Drosophila melanogaster, are documented for the first time using a broad spectrum of modern morphological techniques. External structures of the body wall, the cephaloskeleton, and the musculature are described and illustrated. Additional information about other internal organs is provided. The systematic implications of the findings are discussed briefly. Internal apomorphic features of Brachycera and Cyclorrhapha are confirmed for Drosophila. Despite the intensive investigations of the phylogeny of the megadiverse Diptera, evolutionary reconstructions are still impeded by the scarcity of anatomical data for brachyceran larvae. The available morphological information for the life stages of three insect model organisms -D. melanogaster (Diptera, Drosophilidae), Manduca sexta (Lepidoptera, Sphingidae) and Tribolium castaneum (Coleoptera, Tenebrionidae) - is addressed briefly. The usefulness of a combination of traditional and innovative techniques for an optimized acquisition of anatomical data for different life stages is highlighted.

Effects of microwave radiation and conductive heating on Tribolium castaneum microstructure.

Microwave radiation and conductive heating were used to completely kill adult Tribolium castaneum (Coleoptera: Tenebrionidae) in wheat flour to protect the flour during storage without significantly effecting its quality. The microstructure of T. castaneum was analyzed to reveal the mechanisms leading to death under microwave and heat treatments. Microwave radiation and conductive heating had different effects on the microstructure of the cuticle of adult T. castaneum and on the ultrastructure of the cells of the epidermis, fat body, and midgut. Both treatments caused a large cavity to appear in the nucleus and the disappearance of mitochondria and the Golgi apparatus. After microwave treatment, there was little change in the surface microstructure but the epidermis was of uneven thickness and the four outer layers of the cuticle were thinner. Nuclear size was essentially unchanged, but fat body cells were fewer and coalesced together. In contrast, conductive heating led to a disordered arrangement of cells on the surface of T. castaneum and indistinct boundaries between layers of the cuticle. The nuclei were enlarged and the fat body cells noticeably fewer and indistinct with a scattered distribution. Thus, microwave treatment produced less severe effects on the surface microstructure and cellular ultrastructure of T. castaneum than did conductive heating. It is concluded that these cellular and surface changes were responsible for the death of T. castaneum.

In vitro chitin synthesis in an insect: formation and structure of microfibrils.

Chitin microfibril synthesis in Tribolium castaneum chitin synthetase (CS) assays results in the formation of a considerable precipitate. Such precipitate does not appear in the absence of the CS substrate (uridine diphospho N-acetyl-D-glucosamine) or in the presence of polyoxin-D, a potent CS inhibitor. Diflubenzuron which blocks in vivo chitin synthesis in insects has no effect on the precipitate formation at a relatively high concentration (3 x 10(-4) M). Electron microscopic examination of the CS product reveals a network of long, parallel oriented microfibrils. The microfibrils vary in thickness from 10 to 80 nm. Thinner elements merge to form larger and thicker microfibrils which are packed in distinct bundles. Particles associated with the microfibrils are largely spheroidal and range from about 50 to 250 nm in diameter. Coiled fibroid structures enclosed inside particles were observed. Similar coiled structures or extended fibroids attached to the outside (shell) of particles were also found. The nature of the particles and their possible role in chitin synthesis and fibrillogenesis in insects are discussed.