Mosquitoes contribute to the transmission of life-threatening diseases that include Zika, dengue, chikungunya, Rift Valley fever and malaria. Of these, malaria carries the most risk accounting for 229 million cases and more than 400,000 deaths in 2019. Malaria is caused by parasites that are transmitted to people through the bites of infected female Anopheles mosquitoes. Vector control strategies such as indoor residual spraying and long-lasting insecticidal net programmes have played a crucial part in the reduction of malaria cases. But there are a number of problems with these interventions.
Firstly, insecticide resistance of the majority malarial vectors in Africa is widespread and increasing. With the resistance being prominent, it becomes difficult to overcome this concern. Secondly, and connected to this, is the fact that spraying and nets (either alone or combined) will not eradicate malaria incidences in high transmission areas. In particular, they are not effective in controlling Anopheles vectors. Behaviourally, it has been reported that these feed and rest indoors and have a preference to feed at night.
The research group at the University of Pretoria is working on a project that seeks to answer the question: Why do mosquitoes prefer certain individuals above others?
But before that we need to understand some basic behavioural techniques used by these bloody stingers.
Do all mosquitoes feed on blood?
For most people not belonging to biology background consider that feeding on blood is a characteristic of all the mosquitoes. This, however, is evidently false. The male mosquitoes to not feed on blood. The proboscis of male mosquitoes is not strong enough to pierce through the skin and therefore can’t suck blood flowing underneath it. The female’s proboscis, however is strong enough to pierce through the skin and feed on the blood. This justifies the fact that while females are the true blood suckers, the males are strictly vegetarian in their diet.
Why only female mosquitoes?
The obvious question arising in your mind must be of the reason that lies behind it. Female mosquitoes need a blood meal for their eggs to develop. The reason why only female mosquitoes drink blood is so that they can nourish their child-bearing bodies. Blood is full of proteins and amino acids, which makes it the perfect prenatal supplement for growing mosquito eggs, which is why only female mosquitoes drink blood. When female mosquitoes aren’t drinking our blood, they suffice eating plant nectar just like their male counterparts.
How mosquitoes find a meal?
First, the female mosquito must find its host. It can be quite selective. For example the Culex quinquefasciatus mosquito feeds exclusively on birds.
Locating their preferred host involves a series of behavioural steps. This starts with the mosquito becoming aware of the host. This is usually done using long range cues such as carbon dioxide or visual cues. The female mosquito then uses heat and moisture cues near the host, and finally skin odour cues influence landing and biting site selection. These surface skin chemical cues used for communications within a species are called semiochemicals. Sophisticated analytical techniques are now helping to find the identity of mosquito semiochemicals and potential semiochemical blends. Some chemicals might be working together to attract or repel mosquitoes. Many sampling analysis have led to identification of few compounds which were involved in mosquitoes landing to the biting sites. The compounds identified could be useful in future malaria vector control programmes, acting as attractants or repellents. More biological studies will have to be done to test them on female mosquitoes.