Humidity Perception

Many observations on their behavior indicate that insects are able to monitor the amount of water vapor in the surrounding air. Insects actively seek out a "preferred" humidity in which to rest, or orient themselves toward a source of liquid water. The value of the preferred humidity varies with the physiological state of the insect, especially its state of desiccation. Normally, for example, the flour beetle, Tribolium castaneum, prefers dry conditions; however, after a few days without food and water, it develops a preference for more humid conditions. Ablation experiments have established that humidity detectors are typically located on the antennae, though they occur on the anterior sternites in Drosophila larvae, and surround the spiracles in Glossina, where they monitor the air leaving the tracheal

FIGURE 12.9. A thermo-/hygroreceptive sensillum on the antenna of Bombyx mori. [Redrawn from R. A. Steinbrecht, 1989, The fine structure of thermo-/hygrosensitive sensilla in the silkmoth Bombyx mori: Receptor membrane substructure and sensory cell contacts, Cell Tiss. Res. 255:49-57. By permission of Springer, Berlin.]

FIGURE 12.9. A thermo-/hygroreceptive sensillum on the antenna of Bombyx mori. [Redrawn from R. A. Steinbrecht, 1989, The fine structure of thermo-/hygrosensitive sensilla in the silkmoth Bombyx mori: Receptor membrane substructure and sensory cell contacts, Cell Tiss. Res. 255:49-57. By permission of Springer, Berlin.]

system. Hygroreceptors exist as thin-walled, aporous hairs or pegs that are typically also thermosensitive (Altner and Loftus, 1985). Eachhygroreceptor contains the dendrites of two neurons: the dendrites that penetrate the full length of the hair are hygrosensitive, whereas those that terminate near the base of the hair are temperature sensitive (Figure 12.10). Because they are poreless, hygroreceptors clearly cannot operate in the same manner as chemoreceptors, that is, by water molecules binding to receptors in the dendritic membrane. In fact, it seems that they function as mechanoreceptors, behaving like a hair hygrometer. The sensillar cuticle or a substance associated with it is hygroscopic and undergoes deformations as humidity changes, leading to physical stimulation of the dendrites. It appears that there are two types of hygroreceptors: "moist" receptors respond to increasing humidity, while "dry" receptors are stimulated by a decrease in humidity. In both cases, the stimulus is encoded as an increase in the rate of generation of action potentials.

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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