Location and Structure of Sensilla

Behavioral and electrophysiological experiments have been used to establish the location and nature of chemosensilla. Organs of taste are common on the mouthparts, especially the palps, though they have been identified also on the antennae (Hymenoptera), tarsi (many Lepidoptera, Diptera, and the honey bee), ovipositor (parasitic Hymenoptera and some Diptera), and on the general body surface. The antennae are the primary site of olfactory organs and often bear many thousands of these structures. The mouthparts also carry olfactory structures in many species.

Earlier authors classified chemosensilla according to their morphology, but this system proved inadequate because structures that looked similar at the light microscope level were shown, using electron microscopy combined with electrophysiological studies, to have different structures and functions. Slifer (1970) grouped chemosensilla in two categories, "thick-walled" and "thin-walled," which, though a seemingly simple structural criterion for separation, is valid in all except a few cases, and broadly correlates with their functions as organs of taste and smell, respectively.

Thick-walled (uniporous) chemosensilla (Figure 12.9A) take the form of hairs, pegs, or papillae (Mitchell et al., 1999; Ryan, 2002). Generally, they serve as taste sensilla, though some are also sensitive to strong odors. The chemosensitive hairs and pegs broadly resemble tactile hairs, though they can be distinguished with the electron microscope. Whereas tactile hairs have a sharply pointed top and are innervated by a single neuron whose dendrite terminates at the base of the hair, thick-walled chemosensory hairs have a rounded tip with a terminal pore, multineuronal innervation, and dendrites that extend along the length of the hair to terminate just beneath the pore. The dendrites are usually enclosed in a cuticular sheath. Occasionally, the thick-walled pegs may be set in pits, when they are known as sensilla coeloconica and perhaps have an olfactory function. Papillae having

FIGURE 12.8. (A) Thick-walled chemosensillum; and (B) thin-walled chemosensillum. [A,after E. H. Slifer, J. J. Prestage, and H. W. Beams, 1957, The fine structure of the long basiconic sensory pegs of the grasshopper (Orthoptera; Acrididae) with special reference to those on the antenna, J. Morphol. 101:359-397. By permission of Wistar Press. B, after E. H. Slifer, J. J. Prestage, and H. W. Beams, 1959, The chemoreceptors and other sense organs on the antennal flagellum of the grasshopper (Orthoptera; Acrididae), J. Morphol. 105:145-191. By permission of Wistar Press.]

Beekeeping for Beginners

Beekeeping for Beginners

The information in this book is useful to anyone wanting to start beekeeping as a hobby or a business. It was written for beginners. Those who have never looked into beekeeping, may not understand the meaning of the terminology used by people in the industry. We have tried to overcome the problem by giving explanations. We want you to be able to use this book as a guide in to beekeeping.

Get My Free Ebook

Post a comment