Environmental Neural and Endocrine Interaction

Only very rarely is a physiological event directly influenced by environmental stimuli. Temperature changes, through their effect on reaction rate, can, in poikilotherms at least, alter the rate at which an event is occurring. However, in almost all situations stimuli are first received by sensory structures that send information to the central nervous system to be dealt with. Some of these stimuli require an immediate response, which, as noted earlier in this chapter, is achieved via the motor neuron-effector organ system. The information received by the central nervous system as a result of other stimuli, however, initiates longer-term responses mediated via the endocrine system. This information, then, must be first "translated" within the brain into hormonal language. The center for translation is the neurosecretory system. Depending on the stimulus and, presumably, the site of termination of the internuncial neurons, different neurosecreteory cells will be stimulated to synthesize and/or release their product. This material may then act directly on target organs ("one-step" or "first-order" neurosecretory control) or exert a tropic effect on other endocrine glands ("two-step" or "second-order" control).* A number of examples may be cited to illustrate these two levels of control. In Rhodnius feeding leads to stimulation of stretch receptors in the abdominal wall. Information from these receptors passes along the ventral nerve cord to the composite thoracic ganglion where the posterior neurosecretory cells are stimulated to release diuretic hormone. The latter facilitates rapid excretion of the excess water present in the blood meal (Chapter 18, Section 5). In juvenile Rhodnius similar information is also received by the brain whose neurosecretory cells liberate thoracotropic hormone to trigger a new molting cycle (Chapter 21, Section 6.2). A variety of stimuli may enhance the rate of egg production in the female insect. Copulation, oviposition, pheromones, photoperiod, and feeding are all stimuli that cause neurosecretory cells to release an allatotropic hormone (Chapter 19, Section 3.1.3). The latter activates the corpora allata whose secretion promotes egg development.

* In vertebrates "three-step" ("third-order") neurosecretory control is also found where hypothalamic neurosecretion exerts a tropic effect on specific cells of the anterior pituitary gland. The products of these cells are themselves "tropic" hormones which act on other epithelial endocrine glands.

FIGURE 13.8. Diagrammatic summary of the variety of environmental and other factors that influence neurosecretory activity in insects. [After K. C. Highnam, 1965, Some aspects of neurosecretion in arthropods, Zool. Jahrb. Abt. Allg. Zool. Physiol. Tiere 71:558-582. By permission of VEB Gustav Fischer Verlag.]

Figure 13.8 summarizes the variety of factors, environmental and experimental, that operate via the neurosecretory system to affect physiological events in insects.

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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