Initiation and Regulation of Ingestion by Hematophagous Arthropods

Abstract

Initiation of feeding behavior by a hematophagous arthropod requires correct orientation to the host. Factors involved in orientation are probably more complex in those arthropods which have a higher degree of independence from the host, such as tsetses, but the relative importance of such factors is diminished under laboratory rearing conditions. The primary stimulation for probing activity after alighting on a host is temperature, but other factors act independently or synergistically to elicit or enhance probing. Some blood-sucking arthropods will feed on a free blood surface, while for others the penetration of a membrane, the texture and thickness of which may also be important, appears to be obligatory. In vitro feeding experiments have shown a number of chemical substances in solution to be phagostimulatory following contact with the mouthparts, namely glutathione, nucleotides. chelating agents such as EDTA, amino acids, sugars and salts. A number of metabolic inhibitors can block phagostimulation by these compounds (except in the case of tsetses), while osmotic pressure and pH of potential feeding solutions are also important. Hypotheses have been developed to account for the action of phagostiniulants on mouthpart chemoreceptors, and in a few arthropods, sense organs have been described, and electrophysiological investigations undertaken to demonstrate their action. The strongest phagostimulant for a number of arthropods, adenosine-5′-triphosphate (ATP), is only present in platelets and in erythrocytes, and it is assumed that mouthpart chemoreceptors are in some way able to make contact with it during feeding. However, tsetses can be successfully reared with an in vitro feeding method using defibrinated pig blood as the sole nutrient source, from which platelets and platelet ATP are absent. This fact, coupled with the knowledge that chemical composition of artificial feeding solutions affects the rate and extent of ingestion independently of its effect upon mouthpart chemoreceptors, suggests that phagostimulation, at least in the tsetse, may be more complex than current hypotheses regarding the action of ATP lead us to suppose.