Feeding behaviour in response to blood fractions and chemical phagostimulants in the black‐fly, Simulium venustum

Abstract

ABSTRACT. Wild‐caught black‐flies (Simulium venustum Say complex) were presented with diets at 37°C in an artificial feeding apparatus. Washed human red cells resuspended 1:1 in Ringer solution were potent phagostimulants, causing 89% of flies to gorge. Whole plasma was more potent (32% gorging) than platelet‐poor plasma (2%). The ED50 for red cells was 3.5%. Although ADP, contained in high‐concentration in platelets, was confirmed as a more potent phagostimulant than ATP (ED50 of 5πM V. 12μM), red cells were clearly more phagostimulatory than platelets, and with a potency more than adequate to trigger gorging in vivo. A high response to the ATP analogues, β, γ‐methylene ATP and adenine phosphosulphate, supports the view that the phosphate chain is relatively unimportant in determining nucleotide potency to simuliids. The compounds phytic acid and 2,3‐disphosphoglycerate, potent stimulants to Rhodnius prolixus, produced only moderate and no response, respectively at 1 mM; 5‐hydroxytryptamine, another major constituent of platelets, also produced only a moderate response. Only flies caught while showing a characteristic probing behaviour would subsequently probe and feed in vitro; this ‘blood‐feeding mode’ rapidly disappeared in the absence of stimuli eliciting actual probing, but for flies in this state a small temperature rise was sufficient stimulus for probing.