Metamorphosis of the central nervous system ofDrosophila melanogaster Meigen (Diptera: Drosophilidae) during pupation

We studied the metamorphosis of the central nervous system (CNS) and neighbouring muscles ofDrosophila melanogaster (Diptera: Drosophilidae) during pupation by transmission electron microscopy (TEM). The age of white pupa was assumed to be 0 h and the process of metamorphosis was monitored, onward between 6 and 96 h at 25°C. The profiles in the neuropil showed degeneration at 6 h and its extent increased by 12 h. The presence of glycogen in some of these profiles indicated their larval character. Between 12–18 h, the neuronal profiles became separated from one another, the intervening space was filled with extracellular fluid, and some of the larval synapses degenerated. Synaptic vesicles started reappearing around 18 h and synapses were detectable by 24 h. Neuronal processes compactly filled the neuropil by 65 h and the maturation of synapses continued until 86 h. The degeneration of profiles in the neuropil was found to be bimodal, peaking at 12 and 42 h, and that of cortical cells was unimodal with a peak at 42 h. The number of neuronal profiles increased with the development time, indicating that more branching of neuronal profiles occurs in neuropils as the metamorphosis progresses. Average number of synapses per unit area (or volume) is minimum at 18 h and maximum at 72 h, when the average number of synapse per axon profile is 0.54. Because 2 axon profiles share one synapse, a value close to 0.5 for monad synapses shows that, on an average, each axon profile at least makes one synapse at this stage of development. Subsequently, there is more than 75% of reduction in the number of synapses during 73 and 78 h. In muscles, vacuoles suggesting histolysis appeared by 6 h. Their ultrastructure became deranged between 12–18 h and myoblasts were found to be present since 8 h. Except for a few muscles in the thorax, such as larval oblique muscles and pharyngeal muscles, most of the muscles in the head and thorax lost all the ultrastructural details and histolyzed by 18 h. Around 38 h, imaginai muscles were detectable, and well-developed muscles were found by 55 h. However, myofibrils continued to be added laterally to the preformed muscles even at 96 h. Electron-dense mitochondria (EDMITs) were found in the neuropil, cortex and muscles of pupa, along with mitochondria of characteristic shape and normal appearance. These EDMITs often occurred in large clusters of more than 100, at times near the surface of the tissue. A few of these were enclosed in vacuoles and were darker than the rest of the EDMITs and normal looking mitochondria. Histochemistry with diaminobenzidine showed the presence of cytochrome c and marker enzyme cytochrome oxidase, both in EDMITs and normal mitochondria. EDMITs were not found to be present in any tissue of the adultDrosophila. A preliminary report of the work was presented at the International Conference on Neurobiology at Goa in 1991 and appeared inNervous Systems, Principles of Design and Function (ed.) R N Singh (New Delhi: Wiley Eastern) pp 91–105 (1992).     

Feeding preference of the rice stink bug on annual grasses and sedges

Adults of the rice stink bug, Oebalus pugnax (F.), preferred panicles of vasey grass, Paspalum urvillei Steud., over those of 11 species of other grasses and one species of sedge (Cyperus) associated with cultivated rice, Oryza sativa (L.). The number of feeding adults increased approximately 2 times from 1 h post-infestation (PI) to 6 h PI. The number of feeding females was greater than males at 1 h PI but no different at 6 h PI. Both sexes fed significantly (P<0.05) more on O. sativa panicles than on P. urvillei panicles at 6 h PI. Both sexes also fed significantly (P<0.05) more on 28 and 21 cm long O. sativa panicles than on 7 cm long panicles, but no such differences existed in feeding among P. urvillei panicles.

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Résumé Les adultes d'Oebalus pugnax F. ont préféré les panicules de Paspalum urivillei Stend à celles de 11 autres Graminées et 1 Cypéracée associées au riz cultivé, Oryza sativa L. Le nombre d'adultes s'alimentant a cru environ 2 fois de la lère (1P1) à la 6ème (6P1) heure ayant suivi l'infestation. Le nombre de femelles s'alimentant était supérieur à celui des mâles 1 heure après (1P1), mais ne présentait pas de différence 6 h après l'infestation (6P1). Les 2 sexes s'alimentaient significativement plus (P< 0.05) sur les panicules d'O. sativa que sur celles de P. urvillei 6 heures après l'infestation (6P1). Les 2 sexes se sont alimentés significativement plus (P< 0,05) sur des panicules d'O. sativa de 28 et 21 cm que sur ceux de 7 cm, mais aucune différence n'était observée dans l'alimentation sur les panicules de P. urvillei.