The role of salivary nitrophorins in the ingestion of blood by the triatomine bug Rhodnius prolixus (Reduviidae: Triatominae).

To assist haematophagy, Rhodnius prolixus produces several bioactive molecules in its saliva which it injects into the host skin. The most abundant of these molecules are the nitrophorins (NPs). In this work, we reduced the expression of NP1-4 in the saliva of R. prolixus by RNAi and evaluated the subsequent feeding performance of the bugs using the cibarial pump electromyogram either on the dorsal skin or on the tail vein of the mice. NPs salivary mRNA was reduced by >99% in comparison to controls. Saliva from knockdown nymphs also presented 82% less haemproteins while the total protein was not reduced. Knockdown nymphs feeding on the skin had lower ingestion rates mainly due to the longer cumulative probing time and lower cibarial pump frequency. Another difference was that knockdown insects bit approximately 5 times more. No differences were observed between groups fed on the tail vein. When the feeding sites were compared, nymphs fed on the tail vein had higher effective ingestion rates. These findings endorse the importance of the NPs for the ability of bugs to complete the meal in a short total contact time with a low number of bites, decreasing the perception of the insect by the host.

Blood-feeding performance of nymphs and adults of Triatoma brasiliensis on human hosts.

The blood-feeding behaviour of nymphs and adults of Triatoma brasiliensis fed on the forearm of human volunteers was studied by electronic monitoring of the cibarial pump. Parameters of total contact time (TT), initial weight (IW), weight gain (WG), ingestion rate (IR), pump frequency (F), quantity of liquid ingested per cibarial pump stroke (QLC) and non-ingestive time (NIT) (cumulative probing time and pumping interruptions during blood feeding) were measured. Protein profile (SDS-PAGE) and quantity of proteins of salivary gland extracts (QP) were also determined for each stage. The TT reflects the feeding performance of the insects and differed between instars, varying between 18.3+/-2.5 min for the first instar and 33.9+/-2.3 min for the fifth instar. The observed increase in the IR when comparing different instars was related to the increase in the cibarial pump volume inferred from the QLC data. During development, the volume of the cibarial pump grew asymmetrically determining the different contact times observed among the instars. Males and females presented a remarkable sexual dimorphism in respect to the volume of the cibarial pump, females showing a better performance compared to males. Despite the differences, the results show that each of the development stages of T. brasiliensis was able to obtain a relatively fast bloodmeal, with few interruptions and without causing pain, providing further evidence of the capacity of this species to adapt to domestic environments.