A simple method for marking haematophagous insects during the act of feeding

Blood-meals of two species of haematophagous insects, Glossina morsitans Westw. and Aedes (Stegomyia) aegypti (L.), have been ‘ marked ’ by allowing groups of adults to feed on an ox to which an aqueous solution containing 4 g. of trypan blue had previously been administered intravenously. The dyestuff is detected by a paper chromatographic procedure in which the blood-meal, mixed with 0·1N NaOH, is applied to a narrow strip of Whatman No. 1 chromatographic filter paper and the chromatogram is developed in 0·1N NaOH. Under these conditions, trypan blue remains at the origin, whereas the other coloured components of the blood-meal move away from the point of application. The duration of the mark in the ox and in the insects has been examined. The trypan blue was detected in four out of six fresh blood-meals of Glossina taken 38 days after injection of the dye into the ox, in six out of six examples of Glossina examined two days after blood-meals taken 24 days after the injection, in four out of six examples of Glossina examined eight days after blood-meals taken immediately following the injection, in six out of six examples of Aedes one day after blood-meals taken 14 days after the injection and in six out of six examples of Aedes two days after blood-meals taken immediately following the injection.