The role of physical and chemical stimuli in the development ofin vitrofeeding techniques for tsetse fliesGlossinaspp. (Dipt., Glossinidae)

In laboratory experiments at Langford, Bristol, agar membranes were superior to Parafilm membranes for the in vitro feeding of Glossina morsitans Westw. and G.austeni Newst. Temperature appears to be the primary stimulus for probing but agar membranes stimulate some probing, probably because of the humidity gradient above the membrane. Agar membranes also stimulate gorging, and enhance the effect of the phagostimulant adenosine 5' triphosphate (ATP). Agar membranes may simulate conditions on and in the skin of a living host by stimulating tactile and/or hygroreceptors in the mouthparts of the probing fly. G. morsitans females fed on blood containing ATP concentrations up to 5 × 10 −3 M gave a higher reproductive rate and higher pupal weights. The rate of breakdown of ATP in bovine blood during one hour at 37°C indicated the amounts that need to be added to maintain optimal concentrations during feeding. There was positive correlation between pupal weight and reproductive rate of G. morsitans with the membrane-feeding system, but a maximum of only 80% of the optimal rate of reproduction and 80% of the optimal pupal weight was achieved. On living hosts this correlation did not hold, the pupal weights being higher, suggesting that the membrane-feeding system constitutes a stress factor. The stress of in vitro feeding does not apparently involve probing or gorging stimuli but its symptoms are those of nutritional deficiency. It is concluded that post mortem changes in vertebrate blood may affect quantitative aspects of feeding, or they may affect either the nutritional content of the blood or the ability of the insects to metabolise it correctly.