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Sensilla on the tarsal segments and mouthparts of adult Drosophila melanogaster meigen (Diptera : Drosophilidae)

1983; Elsevier BV; Volume: 12; Issue: 5-6 Linguagem: Inglês

10.1016/0020-7322(83)90023-5

1872-907X

Shubha V. Nayak, Ranjana Singh,

Insect and Arachnid Ecology and Behavior

Sensilla on the tarsal segments of legs and on the external and internal mouthparts of adult Drosophila melanogaster Meigen (Diptera : Drosophilidae) were studied by light and electron microscopy. Tarsi are invested with bracteate and bractless bristles. Ethanolic silver nitrate stain distinguishes dendrite-containing bristles from other hairs on the tarsi. Stained bristles are bractless. Males have more silver-staining bristles than females on the I st 4 tarsal segments of prothoracic legs. There are 33 – 34 taste bristles on each half of the labellum. Many of them are 2-pronged. Both prongs have a pore at the tip, but chemosensory dendrites enter only in one of them. The taste bristles in the 2 medial rows on each half of the labellum are predominantly associated with 4 chemosensory neurons and the peripheral bristles usually contain 2 chemosensory neurons each. Five groups of paired sense organs are known to exist on the internal mouthparts. Amongst 9 sensilla present in the labral sense organ, electron microscopy shows that sensilla numbers 1 – 6 have one mechanosensory neuron each. Sensillum number 7 has 8 neurons with dendrites arranged in 3 groups: 2 triplets and a pair. Sensilla 8 and 9 have 2 neurons each. The ventral cibarial sense organ (VCSO) has 2 sensilla, one with 2 and the other with 4 neurons. Rows of hollow satellite bristles forming 2 sensory systems, dorsal and ventral to the VCSO have one mechanosensory neuron each. The dorsal cibarial sense organ has 2 sensilla on either side of the midline, each containing 3 neurons. The paper describes the fine structural morphology of taste receptors and enumerates axons of all the prominent nerves of mouthparts at different levels. An external nerve loop connecting directly 2 regions of the brain, the tritocerebrum and suboesophageal ganglion, is reported.