The Physiology of Hunger in the Blowfly

The behavior of an animal typically changes as a consequence of feeding and starvation, at least those aspects of its behavior that are adapted to the location and ingestion of food. The physiological basis of such changes has been long sought by vertebrate psychophysiologists, but the underlying mechanisms are still notably obscure. Of animals with simpler or more stereotyped behavior, similar questions have rarely been asked. Owing much to its usefulness in the study of chemoreceptor mechanisms, the blowfly is recently an exception. There have been a number of investigations directed at the mechanisms whereby feeding alters taste sensitivity, readiness to feed, control of intake, locomotor activity, and other behavior in addition to the abundant information regarding the properties of chemoreceptors as they are involved in feeding. We have continued that line of investigation to fill in some of the gaps in the simple, rather thorough picture that has resulted. This paper gives the new evidence we have obtained (referred to herein as Evans and Barton Browne, unpublished), and attempts at the same time to evaluate other pertinent evidence and to present an integrated description of the physiology of in the blowfly. The use of the word hunger in the title requires some comment. It has been used there merely to connote those changes in behavior which are a consequence of feeding and starvation. The term has been avoided elsewhere in this paper in recognition of the difficulties engendered by its use. These difficulties are discussed later in order to make use of the experimental data in that discussion. FEEDING BEHAVIOR In examining the effects of feeding and starvation on the feeding behavior of blowflies, we will consider first the effects on the behavioral threshold of the tarsal contact chemoreceptors and then, using the available data, we will discuss the mechanisms whereby ingestion is controlled. A discussion of the phenomenon of hyperphagia, reported by Dethier and Bodenstein (1958), is also included.