Scents govern most key events in the lives of mosquitoes, and there is extensive research on their sense of smell. A new study reveals how a young female mosquito shifts from focusing entirely on nectar to seeking only blood. An odour receptor that reacts to camphor was found to play a key role.

Rickard Ignell, professor of chemical ecology at the Swedish University of Agricultural Sciences, studies odour-driven behaviours of mosquitoes that spread serious diseases, including the dengue mosquito (Aedes aegypti). In several high-profile studies, he has identified the scents that help blood-seeking females locate their victims.

Now, his research team, together with colleagues in Ethiopia and the US, has investigated a stage in the female mosquito’s life about which we have known considerably less – the transition from being entirely focused on nectar to seeking only blood.

For newly hatched and a few days-old female mosquitoes, nectar-seeking behaviour is extremely important. They need to build up energy reserves to increase their survival, flight capacity and dispersal ability. During sexual maturation, they then develop the ability to consume a blood meal, a process that is accelerated after mating and is linked to a shift towards being attracted to humans.

“Female mosquitoes are equipped with a large number of odour receptors, particularly on their antennae. The receptors function as a kind of ‘lock and key’ mechanism, whereby a single receptor can only be ‘activated’ by certain odours. What we have shown is that a change occurs in a single receptor that completely ‘reconfigures’ the female’s foraging behaviour,” says Rickard Ignell.

The olfactory receptor in question (Or117) was found to be sensitive to camphor and similar substances found in the scent of flowers that these mosquitoes are particularly attracted to. Camphor has a distinctive scent and is found, for example, in Tiger balm.

This receptor proved to be essential for nectar-seeking behaviour in young, unmated females. As they grow older, and after mating, the females cease to be attracted by floral odours, whilst their sensitivity to camphor also diminishes.

“The more we understand about mosquitoes’ sense of smell and the behaviours it controls, the greater our chances of finding ways to manipulate the behaviour of these disease-transmitting insects,” concludes Rickard Ignell.