Sound Reception

Sounds are waves of pressure detected by organs ofhearing. A sound wave is produced when particles are made to vibrate, the vibration causing displacement of adjacent particles. Usually sound is thought of as an airborne phenomenon; however, it should be appreciated that sounds can pass also through liquids and solids. It will be apparent, therefore, that the distinction between sound reception and mechanoreception is not clear-cut. Indeed, many insects that lack specialized auditory organs can clearly "hear," in that they respond in a characteristic manner to particular sounds. For example, caterpillars stop all movements and contract their bodies in response to sound. If, however, their bodies are coated with water or powder, or the hairs removed, the response is abolished. Further, insects with specialized sound sensors may continue to respond to sounds oflow frequency even after the specialized organs have been damaged or removed. The structures that respond to these low-frequency sound waves (see Figure 12.8) are the most delicate mechanosensilla, namely, the sensilla trichodea and, probably, chordotonal sensilla distributed over the body surface. In some species, hairs sensitive to sound may be restricted to particular areas, for example, antennae or cerci.

Among Insecta, hearing has evolved independently in at least 12 groups (Michelsen and Larsen, 1985). Though insect hearing organs include a number of common elements, their structural complexity reflects the interaction of three factors: the evolutionary history of the group, the size of the insect, and the acoustic features of the insect's environment. For example, the tympanal organs of most moths, which are sensitive only to the sounds emitted by bats preying on them, are relatively simple whereas the tympanal organs of crickets and grasshoppers tend to be complex because they need to distinguish the (equally complex) songs of conspecifics.

Broadly speaking, insect-hearing structures can be divided into two categories: near-field detectors and far-field detectors. As their names indicate, the detectors are able to perceive sounds that originate a short distance (from a few millimeters up to about 1 m) or a long distance (tens of meters), respectively. However, there are several other features unique to each type of detector. Near-field detectors are displacement receivers (activated by vibrations of adjacent air particles), are sensitive to low-frequency sound (75-500 Hz), and usually have a relatively simple structure that does not include a tympanum (Romer and Tautz, 1992). Examples of near-field detectors are the hairs on the cerci of cockroaches, on the aristae of Drosophila, and on the thorax of some noctuid caterpillars, as well as the specialized Johnston's organ (Section 3.1). Drosophila males vibrate their wings at about 330 Hz during courtship. The sound produced is picked up by the aristae of a female, provided she is within about 2 mm. If she is unreceptive, she produces her own song (at about 300 Hz) that causes the male to turn away and stop courting (Bennet-Clark and Ewing, 1970). Caterpillars of the noctuid moth Mamestra brassicae have eight fine thoracic hairs that show maximal sensitivity to air-borne vibrations in the 100-600 Hz range. At these frequencies, crawling caterpillars stop moving, and may squirm and lose contact with the

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.

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